Ecological sensitive area urban open cut tunnel group construction method

Abstract

The invention discloses a method for constructing an urban open-cut tunnel group in an ecological sensitive area. The method comprises the following steps: step 1, confirming construction; step 2, enclosure construction; thirdly, a foundation pit is excavated; 4, supporting construction is conducted; 5, main body construction; sixthly, auxiliary engineering construction is conducted; according to design requirements, each tunnel is divided into a plurality of foundation pits, each foundation pit is provided with two working faces, line production takt is formed between procedures, competition between the working faces is formed, a reward and penalty incentive mechanism is formulated, a typical mechanism is established, and on the premise that engineering safety is guaranteed, construction of the multiple tunnels is conducted at the same time. The implementation of a standardized construction site and the on-time and on-time implementation of a construction progress target are ensured, and the construction efficiency is improved; the construction quality of a tunnel main body structure is effectively guaranteed through dewatering and drainage of the foundation pit and waterproof construction of the tunnel; the advanced foundation pit safety management method is summarized according to foundation pit deformation monitoring data under the urban multi-bin excavation condition.

Description

[0001] This application claims the priority of a Chinese patent application with an application date of January 22, 2025 and an application number of 202510102632.7, the entire content of which is incorporated herein by reference. Technical Field

[0002] The present invention relates to the technical field of tunnel group construction, and particularly to a method for constructing an open-cut tunnel group in an ecological sensitive area of a city. Background Art

[0003] With the progress of urban construction and the development of urbanization, in order to meet the requirements of economic globalization and the information age, it is necessary to adjust the urban layout, strengthen the construction of urban infrastructure, improve the quality of urban construction, and vigorously develop the tertiary industry to meet the increasing living needs;

[0004] The increasingly large urban resident population and the continuous pursuit of the quality of life demand bring an increasing urban traffic pressure year by year. The existing traffic system can no longer meet the urban travel requirements. The construction of urban underground tunnels will greatly relieve the urban traffic pressure, facilitate the travel of people, and accelerate the flow of people and urban development;

[0005] However, there are still deficiencies in the existing urban tunnel construction. The existing urban tunnel construction is mainly the gradual construction of single tunnels, and the construction efficiency is relatively low. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for constructing an open-cut tunnel group in an ecological sensitive area of a city.

[0007] To achieve the above purpose, on the one hand, the present invention provides the following technical solution: A method for constructing an open-cut tunnel group in an ecological sensitive area of a city, including the following steps: Step 1: Construction confirmation; Step 2: Retaining structure construction; Step 3: Foundation pit excavation; Step 4: Support structure construction; Step 5: Main structure construction; Step 6: Construction of auxiliary projects.

[0008] In the above Step 1, confirm the construction sequence before and after the segmented construction of the tunnel and conduct corresponding traffic diversion;

[0009] In the above Step 2, construct the tunnel retaining structure;

[0010] In the above Step 3, conduct the excavation of the tunnel foundation pit;

[0011] In the above Step 4, construct the support structure project;

[0012] In the above Step 5, construct the main structure of the tunnel;

[0013] In the above Step 6, backfill the soil and construct the remaining structure projects.

[0014] As a further technical solution of the present invention, in the first step, the geographical location, surrounding environment and traffic flow of the tunnel group are obtained, the lengths, widths and burial depths of multiple tunnels in the tunnel group are obtained, the multiple tunnels in the tunnel group are divided into multiple construction sections, and the construction sequences of each open-cut tunnel and construction section in the tunnel group are determined; during the construction period, a temporary road is set up, and traffic signs and markings for guiding vehicles and pedestrians to pass in an orderly manner are set on the temporary road. According to the traffic flow and road conditions during the construction period, the timing and phase of traffic lights are adjusted to improve the traffic capacity of the road. In addition, traffic warning signs and warning lights during the construction period are set; an open-cut tunnel is determined as the first construction section of the tunnel group, and other open-cut tunnels start construction in sequence according to the progress of pipeline relocation, and each tunnel is constructed in parallel.

[0015] Optionally, in the second step, bored cast-in-place piles and secant bored piles are constructed first. For the bored piles, a full casing and a rotary drilling rig are used. The bored cast-in-place piles and high-pressure jet grouting piles form a cut-off curtain. The adjacent single secant bored piles are mutually overlapped to form a pile wall. Among them, for the bored cast-in-place piles, a reinforced concrete guide wall is first constructed above the pile top. The width of the guide wall is 3.5 meters, the thickness is 35 cm, and the material is C25 concrete. Subsequently, the pile center position is accurately measured as the control point for the rig positioning. After the pile foundation is in place, the soil with a depth of 2.5 meters to 3 meters is removed to clear obstacles. Then, a steel casing is sunk into the completely weathered rock layer by a pile driver. The verticality is detected to see if it reaches the preset verticality. If it does not reach the preset verticality, the verticality is corrected. If it reaches the preset verticality, soil is taken downward until the designed bottom elevation of the hole is reached. Subsequently, a steel reinforcement cage is fabricated and hoisted by a crane. The designed elevation is determined by the elevation of the top of the casing. When the steel reinforcement cage is lowered, it is gradually lowered by positive rotation or reverse rotation to prevent collision. After being lowered to the designed elevation, it is fixed. Subsequently, concrete is poured. For the reinforced piles, underwater C35 concrete is used, and for the plain piles, super-retarding C35 concrete is used. The concrete pouring conduit is connected by a screw thread with a rubber sealing ring, with an inner diameter of 25 cm. The conduit is lowered into the hole by a crane. The bottom of the conduit is 30 - 50 cm higher than the bottom of the hole to ensure the discharging space at the lower opening. The upper opening of the conduit is connected to a concrete funnel, and the upper opening of the conduit is sealed with a water-stop plug. The concrete flows into the funnel through a chute. After more than 2 cubic meters of concrete is stored in the funnel, the bottom cover of the funnel is pulled out, and concrete is poured into the conduit, and the concrete pouring is maintained continuously. After the pouring starts, continuous construction is carried out. During the pouring process, the actual height of the concrete surface is measured and the buried depth of the conduit is calculated to make the bottom end of the conduit buried 2 meters to 6 meters below the concrete surface. After the concrete pouring is completed, the casing and the conduit are gradually removed, with 1 - 2 sections of the conduit removed each time. After the conduit is removed, it is washed. When the casing is lifted, the casing is pulled out upward and shaken left and right to enable the concrete to flow into the space occupied by the casing. The buried depth of the casing is controlled at about 2 meters. The concrete is poured to 0.5 meters above the pile top elevation, and this part of the concrete is chiseled off before constructing the capping beam. After the pouring is completed, the casing and the conduit are pulled out. The setting time of the plain pile concrete is determined according to the single-pile construction time. The setting time of the plain pile concrete can be determined according to the following method. First, the time t required for a single-pile construction is measured, and then it is calculated according to the following formula: T = 3t + K, where: T = the setting time of the plain pile concrete, K = the reserve time, generally taking 1.5t, t = the single-pile construction time of pile A and the single-pile construction time of pile B. During the pressing-down process of the casing, the verticality during the pressing-down process of the casing is detected using plumb bobs from two mutually perpendicular directions, and any deviation is corrected immediately when found;

[0016] Among them, for the construction of high-pressure jet grouting piles, first level the site, dig sewage ponds and sewage ditches, make slurry ponds, mark the pile points clearly, use the self-propelled function of the drill rig to move the drill rig to the designed hole position, use a theodolite to adjust the verticality, align the drill bit with the pile point, and use a plumb bob to check at any time during drilling. The inclination of the drill pipe is less than or equal to 0.5%, and the deviation between the drilled hole position and the designed hole position is less than or equal to 50 mm. After the drill rig is in place, first conduct a water jet test at 0.5 MPa. Move the debugged drill rig to the designed hole position, adjust the verticality, and align the drill bit with the center of the designed pile position. After the water jet test, start drilling. The water jet pressure increases from 0.5 MPa to 1 MPa. When the first drill pipe is drilled, stop the water jet. After the pressure drops, connect the drill pipes and continue water jet drilling until the designed pile bottom position is reached. Subsequently, use 42.5 composite Portland cement and clean drinking water to prepare according to the preset mix ratio. The cement content is greater than or equal to 25%. According to the determined mix ratio, first add water to the bucket, then add cement, start the mixer to mix, flow through the filter screen into the slurry pond, and then pump it into the second filter screen with a slurry pump. After the second filtration, the slurry flowing into the slurry bucket is pressurized by a high-pressure pump, sent to the drill rig through a high-pressure pipe for jet grouting. Among them, the slurry pressure is greater than 3 MPa, the water pressure is 25 MPa, the slurry water-cement ratio is 0.8, the rotation speed is 10 revolutions per minute, and the lifting speed is 10 cm per minute. After drilling to the designed elevation, unscrew the upper drill pipe, put in steel balls to block the water jet holes, and then install the drill pipe. Then, send high-pressure cement slurry to the drill rig. After the slurry emerges from the bottom of the hole, the drill pipe starts to rotate and lift, and jet grouting is carried out from bottom to top. During the jet grouting process, the amount of slurry overflow is controlled at 10% - 25%. When encountering gravel soil, re-jet grouting is carried out, and the re-jet grouting height is greater than or equal to 500 mm. During the rotation process, when the first drill pipe is lifted out of the ground, stop grouting. After the pressure drops, remove the drill pipe. When the designed pile top elevation is reached, start the jet grouting pile again. When the designed pile top elevation is reached, carry out low-pressure supplementary jet grouting. After the low-pressure supplementary jet grouting is completed, lift out the drill pipe and drill bit for low-pressure water jetting to wash the drill pipe and nozzle, and move the drill rig. After one pile is jet grouted, move the drill rig away and carry out the operation of the next pile. The construction interval between adjacent two piles is greater than or equal to 2 days, and the spacing is greater than or equal to 2 meters.

[0017] Optionally, in the second step, dewatering and drainage construction of the foundation pit is carried out. For the dewatering construction of the foundation pit, first, the dewatering wells are drilled. The construction process flow includes well point measurement and positioning, excavation of the wellhead, installation of the casing, rig positioning, drilling, hole cleaning, lowering of the well pipe, backfilling of the filter layer between the well pipe and the hole wall, well washing, installation of a water pump inside the well pipe, installation of the pumping control circuit, trial pumping, normal operation of the dewatering well, and pulling out the well pipe and sealing the well after the dewatering is completed. Before construction, a dewatering test is carried out to adjust the layout, quantity, structural dewatering index, and dewatering monitoring of the dewatering well points. As soon as a dewatering well is constructed, it is put into operation immediately to timely lower the groundwater level and keep running around the clock. The foundation pit excavation is carried out two weeks after pre-dewatering. When the foundation pit is excavated to the base, except for the reserved drainage outlets, the remaining pipe wells are pulled out and backfilled, and a cushion layer is constructed. First, the water is pumped out with a water pump, and then the pipe wells are backfilled with coarse sand to the bottom elevation of the cushion layer, and the well pipes are filled with concrete of the same grade as the cushion layer. At the same time:

[0018] Establish a dynamic monitoring network for groundwater along the line. Use the standby wells outside the pit as observation wells to observe the daily monitoring data of the groundwater level, the monthly monitoring data of the groundwater quality, the daily drainage volume data of the foundation pit, and the drainage sand content data.

[0019] Establish a settlement monitoring network. Before the implementation of the dewatering project, settlement monitoring points are arranged according to the preset pumping influence range and the buildings within the pumping influence range. Continuous settlement monitoring is carried out during pumping. If the cumulative settlement amount is close to the warning value, necessary measures are taken in a timely manner. If it is found through settlement monitoring that the settlement of the building has reached a dangerous level, pumping is stopped. When it is confirmed that the building settlement is caused by dewatering, a recharging measure is taken, and recharging is carried out using the standby wells outside the pit in the settlement area. The distance between the recharge well and the dewatering well is greater than 5.0 meters. Subsequently, the foundation pit drainage construction is carried out. Drainage ditches are set around or in the middle of the excavated foundation pit, and a sump is set every 15 meters, so that the seepage water and construction wastewater in the foundation pit flow into them, and then are pumped into the surface sedimentation tank by a water pump and discharged into the municipal pipe network after sedimentation treatment. The drainage ditches and sumps are deepened while excavating, and the bottom of the ditch is kept more than or equal to 0.5 meters lower than the bottom of the foundation pit, and the sump is kept more than or equal to 0.5 meters lower than the bottom of the ditch. Brick drainage ditches with a size of 400 mm × 400 mm are set on the ground around the foundation pit, and sedimentation tanks with a size of 1000 mm × 500 mm × 500 mm are set every 20 meters. During the excavation process, the dewatering in the pit is maintained to ensure that the groundwater is more than 1 meter below the excavation surface. The dewatering time lasts until the topsoil covering is completed. The foundation pit dewatering is carried out 15 to 20 days before the earth excavation, and the trial dewatering work is done well. When excavating to the construction floor slab, temporary drainage holes are set on the floor slab, and the holes are sealed after the topsoil covering and the internal paving layer construction are completed. The dewatering outside the foundation pit is carried out 7 to 10 days before the foundation pit excavation, and the water level is lowered to 5 meters below the ground surface. One drainage hole is arranged for every 200 square meters.

[0020] Optionally, in the third step, foundation pit excavation and support erection construction are carried out. During foundation pit excavation and support, earth excavation adopts a full-layer or stepped-layer excavation method, with the layer thickness less than or equal to 2 meters. During the excavation process, the temporary slope on the excavation surface is less than or equal to 1:1.5. Excavation is carried out in layers, and the next layer is excavated after the support is completed. During the excavation process, the leakage positions on the retaining wall are blocked. For the soil within 30 cm above the designed bottom elevation of the foundation pit, the locally excavated depressions are filled with sand, and sump pits are set up to pump out the accumulated water at the bottom of the pit.

[0021] Optionally, in the fourth step, the construction of the reinforced concrete crown beam and the reinforced concrete support beam is carried out. The technological process is the leveling, compaction of the soil under the support beam, measurement and setting out, laying of the bitumen felt isolation layer, steel bar binding, formwork installation, acceptance of steel bars and formwork, concrete pouring and curing. Before the construction of the retaining piles, a concrete guide wall is set up first. The outer guide wall is used as a retaining wall for excavation. After the construction of the retaining pile retaining structure is completed, the inner guide wall is demolished and loaded and transported out together with the soil, and the concrete debris, soil and impurities within the wall top range are removed and washed clean with water. According to the design elevation, the positions of each reinforced concrete purlin and support are set out by using a level and according to the foundation pit retaining wall axis, and the foundation pit bottom is cleaned to ensure the horizontal of the foundation pit bottom. The bottom formwork of the support adopts a C20 concrete bottom formwork with a thickness of 15 cm and a width 15 cm wider than the width of the support beam. After the earth excavation and leveling are completed, the foundation pit bottom is tamped, leveled with gravel, and the two sides are provided with a fixed wooden formwork with a thickness of 4 cm. Concrete is poured, and the concrete is vibrated solid by a flat vibrator. After the surface is pressed twice with a wooden wedge, it is pressed smooth with an iron plate. After the concrete bottom formwork is poured, it is covered with straw bags and watered for curing for 3 days. After the strength of the concrete bottom formwork reaches 50%, the steel bars are bound. A layer of isolation layer is set on the surface of the concrete bottom formwork. Before the steel bar binding, steel pipe scaffolds are erected on both sides and one side of the support beam. After the steel bar binding is formed, the steel pipe scaffolds are removed. The steel bar framework is placed on the bottom formwork. The crown beam, concrete support and concrete corner brace are erected with composite formwork. The support system is jointly stressed by using 50×80 wooden squares, 48×3.5 short steel pipes, M12 tie bolts and fasteners. The surface of the formwork is flat, the joints are tight, and there is no leakage of slurry. For the parts with non-straight diameters and local unevenness, they should be repaired and corrected in time, otherwise they cannot be used. Release agent is applied before formwork erection, and the release agent adopts clear engine oil. The formwork support adopts steel pipes with a diameter of 48 mm, the length of the steel pipe is 1.8 m, and it is driven into the soil by more than or about 0.6 m, with a spacing of 80 cm and two longitudinal steel pipes connected. Before pouring, the position, elevation, cross-sectional dimensions of the formwork, the stability of the formwork and support, and the joint conditions are rechecked. The concrete adopts commercial concrete, and the commercial concrete is transported to the site by a drum-type transport vehicle with a capacity of 6 cubic meters or 8 cubic meters and pumped to each pouring point by a truck pump or a stationary pump. The truck pump selects a concrete pump truck with a boom length of 21 m. The truck pump or the stationary pump is parked on the construction access road for pumping. The formwork of the crown beam, concrete support and concrete corner brace is removed when the concrete strength can ensure that the surface and edges and corners are not damaged due to formwork removal after the concrete has finally set. The concrete is cured by watering and moisturizing, and the surface is covered with burlap, and the production water of the construction site water supply system is used. The curing time is 7 days. After the concrete strength of the crown beam, concrete support and concrete corner brace reaches 95%, the lower layer of earth excavation is carried out; the demolition method of the foundation pit concrete support is mechanical cutting and breaking. The demolition sequence of the support is to first demolish the secondary support, and then demolish the opposite support. When demolishing the support beam, the connecting rod is demolished first and then the main support. When demolishing each support beam, cutting starts from the middle. When demolishing the support, the protection of the wall panel is strengthened to prevent the support beam from damaging the roof slab of the tunnel main structure. Protection measures such as laying wooden squares on the roof slab are taken.

[0022] Optionally, in the fifth step, for the construction of the main structure, first carry out construction preparation work. After the foundation pit is excavated to the designed elevation, conduct foundation pit inspection and structural measurement lofting; then carry out the construction of the plain cushion layer. The cushion concrete is C20 and 20 cm thick. The cushion construction is carried out after the excavation surface. Drain the accumulated water in the foundation pit, remove the loose soil in the foundation pit, clean and level the top of the anti-pulling pile, as well as silt and other sundries. After the foundation pit is cleaned, tamp the base with a rammer and measure the bearing capacity of the foundation. When paving the cushion concrete, control the surface elevation according to the pre-buried horizontal piles. The concrete vibration is carried out with a flat vibrator. Before the cushion concrete sets and after it begins to set, carry out secondary surface finishing on the surface layer and fully cure it to prevent looseness, sanding, and peeling. Control the pouring thickness of the cushion according to the pre-buried elevation control piles, and carry out surface finishing and curing to ensure that the cushion surface has no honeycombing, pockmarks, and cracks; then carry out the support layout. The support for the concrete construction of the main structure framework is a full hall disc buckle support. Each disc buckle vertical pole in the full hall disc buckle support can bear a vertical load of 8 to 9 tons. The vertical load includes the side pressure of the side wall concrete, the weight of the top plate concrete, the weight of the formwork, the construction load, and the wind force acting on the formwork support. The longitudinal and transverse spacing of the disc buckle support is 60 cm and 90 cm, and the transverse spacing of the disc buckle support adjacent to the upper chamfer is 60 cm; then carry out the formwork construction. The external formwork for the concrete project uses the side wall of the retaining structure. Before the construction of the side wall, first trim the wall surface of the retaining structure flat. The formwork consists of a bottom formwork, a side wall formwork, and a top formwork, which are assembled on-site. The construction formwork for the bottom plate and a section of the side wall uses large steel formwork, which is processed into a frame with angle steel and channel steel. The plywood is connected to the frame as a whole and processed into blocks for on-site assembly. The formwork uses 2440 mm × 1220 mm × 15 mm plywood as the panel, 60 mm × 80 mm square wood as the secondary joist, and φ48*3.5 mm steel pipe as the main joist. The outer side wall is poured up to 30 cm above the bottom plate axil angle during the pouring of the bottom plate concrete. Two rows of vertical embedded bolts are arranged on the outer side wall. The upper row is the tie bolt, and the lower row of embedded bolts is welded to the main reinforcement of the structure and does not penetrate the entire bottom plate to prevent the movement of the formwork. The longitudinal spacing of the bolts is 600 mm, and the vertical spacing is 500 mm. The secondary joist uses 60 mm * 80 mm square wood, the main joist steel pipe is arranged vertically, and a steel pipe tie is set at the top. The side wall formwork system for the main structure in the open cut section adopts single-sided formwork and uses a steel triangular truss and embedded parts as the formwork support system to fix the formwork firmly. The formwork panel is 4.5 m × 1.A 5-meter-long and 5-millimeter-thick integral large steel formwork. The four peripheral ribs are made of 75-millimeter-by-8-millimeter steel plates, the vertical secondary ribs are 75-millimeter-by-50-millimeter angle steels, and the transverse direction is connected by 70-millimeter-by-6-millimeter steel plates. The spacing of the secondary back ribs is less than 300 millimeters. The main back ribs on the vertical ribs are 10# double channel steels welded to the back ribs. The support adopts double 14# channel steel triangular frames with a spacing of 750 millimeters. For the top plate formwork system of the main structure in the open-cut section, steel pipe scaffolds, adjustable supports, secondary rib square timbers and main rib steel pipes are used for support. The formwork uses 2440-millimeter-by-1220-millimeter-by-15-millimeter plywood as the panel, and two forms of secondary ribs are adopted: 8*8-centimeter square timbers @30 centimeters and double-pin Φ48 steel pipes @30 centimeters. 10# I-beams @80 centimeters are used as the main ribs. A full hall scaffold is erected with a disc buckle support. According to the two forms of disc buckle supports 48 and 60, the transverse spacing of the support is 90 centimeters, and the longitudinal spacings are 60 centimeters, 90 centimeters and 120 centimeters. The erection step distance is all 1.5 meters. The cut edges of the formwork are protected with edge-sealing paint. The wooden formwork is processed on the construction site. Bottom ribs are set at the formwork joints of the top plate, and sponge strips are added to seal the joints of the vertical formwork. Cleaning ports are set at the top plate and the ends. Before pouring concrete, a dust collector is configured to clean the sundries in the formwork. Thin sponge pads are embedded or putty is applied at the joints to eliminate the gaps. Before erecting the formwork, the formwork is polished, rust-removed, oiled and trial-assembled. When erecting the formwork, the embedded parts are installed and fixed. The formwork release agent uses clean engine oil or release agent. The exposed length of the adjustable screw rod does not exceed 2 / 3 of the total length of the screw rod. Before the formwork enters the site, the formwork is numbered and the use parts are numbered, and the formwork is arranged to enter the site in batches in an orderly manner to meet the requirements of on-site construction and avoid occupying more space on the site. After the base waterproof coating is constructed to meet the requirements, the bottom plate steel bars are tied. The side wall and top plate steel bars are tied after the bottom plate concrete construction is completed and the inner formwork and bottom formwork are installed, and various joint steel bars are reserved according to the design. Subsequently, concrete pouring is carried out. First, the bottom plate concrete is poured. The concrete pouring adopts the inclined layer method and reaches the top at one time. The thickness range of each layer is 30 centimeters to 40 centimeters. The concrete pump truck starts pouring from the four corners on both sides of the foundation pit, allowing the concrete to flow naturally to form an inclined plane. Then, the middle partition wall and the outer side wall concrete are poured. For the tunnel concrete structure, first, the middle partition wall is poured, and then the outer side wall is poured. The inclined layer construction method is used to control the one-time pouring height, and the concrete is fed and vibrated in layers, and the cycle is advanced as a whole. The thickness of each layer is 30 centimeters. Two concrete pump trucks are used for pouring at the same time, and the side walls and the middle wall on both sides of the frame are poured symmetrically at the same time. Then, the top plate concrete is poured. The concrete pouring adopts the inclined layer method and reaches the top at one time. The thickness range of each layer is 30 centimeters to 40 centimeters. The concrete pump truck starts pouring from the four corners on both sides of the foundation pit, allowing the concrete to flow naturally to form a certain inclined plane. Then, concrete vibration is carried out. The concrete is vibrated with an inserted vibrator. The moving distance of the vibrator does not exceed 1.It is 5 times, and insert it 5 cm to 10 cm into the lower-layer concrete. The concrete is tamped densely without missing vibration, under-vibration or over-vibration. The quick-insertion and slow-withdrawal method is adopted, and the vibration points are arranged evenly. Vibration should be strengthened at construction joints and embedded parts. During vibration, do not touch the formwork, steel bars, waterstop belts, and the bottom and top slabs. After the top slab concrete is vibrated densely, before final setting, level, compact and polish the surface original mortar. If the moisture on the vibrated surface is greater than the preset amount, use a vacuum pump and connect a 15-square-meter vacuum suction pad to suck away the accumulated water on the concrete surface area, and then carry out the maintenance of the concrete. After the concrete pouring is completed and initial setting occurs, sprinkle water for maintenance to ensure that the concrete surface is in a wet state, and at the same time cover the concrete surface with geotextiles; carry out tunnel waterproof construction. First, determine the self-waterproofing of the concrete structure. The waterproof concrete is prepared by adjusting the mix ratio and adding admixtures and admixtures. Determine the impermeability grade of the structural concrete, the water-binder ratio of the structural concrete, and the minimum dosage of the binder material according to the strength of the concrete structure and the buried depth of the structure. The top slab concrete and the side wall concrete poured together with the top slab adopt the addition of an appropriate amount of high-quality fly ash and slag to reduce dry shrinkage and temperature difference shrinkage; then carry out the construction of waterproof coiled materials. The side wall adopts a 1.5-mm-thick pre-laid polymer waterproof coiled material, the bottom slab adopts a 1.5-mm-thick pre-laid polymer coiled material, and the top slab adopts a flexible waterproof layer. The waterproof construction progress is consistent with the main structure construction progress. The waterproof coiled material construction of the bottom slab is carried out for each construction flow section after the foundation pit excavation cushion layer is completed. The construction of the waterproof coiled material of the bottom slab for each flow section is controlled to be completed within 2 working days. The construction of the pre-laid polymer waterproof coiled material on the side wall is completed before the tunnel side wall construction. Each flow section is completed within 5 days. The single-component polyurethane waterproof coating on the top slab is completed within 2 working days after the top slab construction is completed and conditions are met. The 7-cm-thick C20 fine aggregate concrete protective layer is constructed after the waterproof coiled material construction is completed.

[0023] Optionally, in step six, carry out earth backfilling. The earth is spread by a bulldozer with a layer thickness not greater than 30 cm. The two sides of the tunnel frame are backfilled according to the backfilling construction of the bridge culvert back. Use a rammer with an impact force range of 1 ton to 3 tons to compact. The top slab filling is carried out according to the filling process of the upper part of the bridge. Use a roller to statically press within 50 cm of the top slab, and use a dump truck with a loading range of 10 tons to 15 tons to load earth for the part greater than 50 cm thick. The bulldozer cooperates with the grader to spread and level, and the roller vibrates and compacts with a compactness not less than 95%. After filling one layer, continue to fill and carry out the next process construction. Subsequently, carry out the construction of the anti-collision wall on the top of the open section. When constructing the bottom slab, a number of iron parts are embedded in an orderly manner. These iron parts are used to reinforce and support the U-shaped retaining wall concrete and the anti-collision wall. The anti-collision wall on the top of the open section retaining wall is constructed after the retaining wall concrete reaches the preset strength. The formwork erection and concrete pouring of the open section retaining wall and the anti-collision wall are the same as those of the tunnel main structure.

[0024] Optionally, in Step 6, first carry out the electrical installation works, including tunnel power supply and distribution, tunnel dynamic power distribution, tunnel lighting, lightning protection and grounding, pump house and auxiliary building lighting, tunnel management center, computer network system, closed-circuit television monitoring system, traffic video monitoring, automatic control system for mechanical and electrical equipment, fire alarm and linkage control system, wired broadcast system, emergency telephone system, wireless communication system, and UPS uninterruptible power supply system; then carry out the installation and commissioning of tunnel fans and control boxes; finally carry out the construction of decoration works, fire protection, and landscape works.

[0025] On the other hand, a method for constructing an urban open-cut tunnel group in an ecologically sensitive area is provided, including the following steps: Step 1: Construction confirmation; Step 2: Enclosure construction; Step 3: Foundation pit excavation; Step 4: Support construction; Step 5: Main body construction; Step 6: Auxiliary project construction;

[0026] In the above Step 1, obtain the geographical location, surrounding environment, and traffic flow of the tunnel group, obtain the lengths, widths, and burial depths of multiple tunnels in the tunnel group, divide the multiple tunnels in the tunnel group into multiple construction sections, determine the construction sequence of multiple open-cut tunnels and construction sections in the tunnel group; during the construction period, set up temporary roads, and traffic signs and markings for guiding the orderly passage of vehicles and pedestrians are set on the temporary roads. According to the traffic flow and road conditions during the construction period, adjust the timing and phase of traffic lights to improve the traffic capacity of the road. In addition, set traffic warning signs and warning lights during the construction period; determine an open-cut tunnel as the first construction section of the tunnel group, and other open-cut tunnels start construction in sequence according to the progress of pipeline relocation, and each tunnel is constructed in parallel;

[0027] In the second step mentioned above, bored cast-in-place piles and secant bored piles are constructed first. For the bored piles, a full casing and a rotary drilling rig are used. The bored cast-in-place piles and high-pressure jet grouting piles form a cut-off curtain. The adjacent single piles of the secant bored piles are mutually occluded to form a pile wall. Among them, for the bored cast-in-place piles, a reinforced concrete guide wall is first constructed above the pile top. The width of the guide wall is 3.5 meters, the thickness is 35 cm, and the material is C25 concrete. Subsequently, the center position of the pile is accurately measured as the control point for the positioning of the drilling rig. After the pile foundation is in place, the soil with a depth of 2.5 meters to 3 meters is first removed to clear obstacles, and then the steel casing is sunk into the completely weathered rock layer using a pile driver. The verticality is detected to see if it reaches the preset verticality. If it does not reach the preset verticality, the deviation of the verticality is corrected. If it reaches the preset verticality, the soil is excavated downward until the designed bottom elevation of the hole is reached. Subsequently, the steel reinforcement cage is fabricated and hoisted using a crane. The designed elevation is determined by the elevation of the top of the casing. When the steel reinforcement cage is lowered, it is gradually lowered by positive rotation or reverse rotation to prevent collision. After it is lowered to the designed elevation, it is fixed. Subsequently, concrete is poured. For the reinforced piles, underwater C35 concrete is used, and for the plain piles, super-retarding C35 concrete is used. The concrete pouring conduit is connected by a screw thread with a rubber sealing ring, with an inner diameter of 25 cm. The conduit is lowered into the hole using a crane. The bottom of the conduit is 30 to 50 cm higher than the bottom of the hole to ensure the discharging space at the lower opening. The upper end of the conduit is connected to a concrete funnel, and the upper end of the conduit is sealed with a water-stop plug. The concrete flows into the funnel through a chute. After more than 2 cubic meters of concrete is stored in the funnel, the bottom cover of the funnel is pulled out, and concrete is poured into the conduit, and the concrete is continuously poured. After pouring starts, continuous construction is carried out. During the pouring process, the actual height of the concrete surface is measured and the buried depth of the conduit is calculated to ensure that the bottom end of the conduit is buried 2 meters to 6 meters below the concrete surface. After the concrete pouring is completed, the casing and the conduit are gradually removed, and 1 to 2 sections of the conduit are removed each time. After the conduit is removed, it is washed. When the casing is lifted, the casing is pulled out and shaken left and right to enable the concrete to flow into the space occupied by the casing. The buried depth of the casing is controlled at about 2 meters. The concrete is poured to 0.5 meters above the pile top elevation, and this part of the concrete is chiseled off before constructing the capping beam. After the pouring is completed, the casing and the conduit are pulled out. The retardation time of the plain pile concrete is determined according to the single-pile construction time. The retardation time of the plain pile concrete can be determined according to the following method. First, the time t required for a single-pile construction is measured, and then it is calculated according to the following formula: T = 3t + K, where: T = the retardation time of the plain pile concrete, K = the reserve time, generally taking 1.5t, t = the single-pile construction time of pile A and the single-pile construction time of pile B. During the pressing process of the casing, the verticality during the pressing process of the casing is detected using plumb bobs from two mutually perpendicular directions, and any deviation is corrected immediately when found;

[0028] In the third step above, the foundation pit excavation and support erection construction are carried out. During the foundation pit excavation and support, the earth excavation adopts the overall layered or stepped layered excavation method, with the layered thickness less than or equal to 2 meters. During the excavation process, the temporary slope on the excavation surface is less than or equal to 1:1.5. The excavation is carried out in layers, and the next layer is excavated after the support is completed. During the excavation process, the leakage positions on the retaining wall are blocked. For the soil within 30 cm above the designed bottom elevation of the foundation pit, the locally excavated depressions are filled with sand, and a sump is set up to pump out the accumulated water at the bottom of the pit.

[0029] In the above step 4, the construction of the reinforced concrete crown beam and the reinforced concrete support beam is carried out. The technological process is the leveling, compaction, measurement and setting out, laying of asphalt felt isolation layer, steel bar binding, formwork installation, acceptance of steel bars and formwork, concrete pouring and curing of the soil under the support beam. Before the construction of the retaining pile, a concrete guide wall is set up first. The outer guide wall is used as a retaining wall for excavation. After the construction of the retaining pile retaining structure is completed, the inner guide wall is removed and loaded and transported out together with the soil, and the concrete debris, soil and impurities within the wall top range are eliminated and washed clean with water. According to the design elevation, the positions of each reinforced concrete collar and support are set out by using a level and according to the foundation pit retaining wall, and the foundation is cleaned to ensure the flatness of the foundation pit bottom. The bottom formwork of the support adopts C20 concrete bottom formwork with a thickness of 15 cm and a width 15 cm wider than the width of the support beam. After the earthwork excavation and leveling are completed, the foundation is tamped, leveled with gravel, and the two sides are provided with a fixed wooden formwork with a thickness of 4 cm. The concrete is poured, and the concrete is vibrated solid by a flat vibrator. After the surface is pressed twice with a wooden wedge, it is polished with an iron plate. After the concrete bottom formwork is poured, it is covered with straw bags and watered for curing for 3 days. After the strength of the concrete bottom formwork reaches 50%, the steel bars are bound. A layer of isolation layer is set on the surface of the concrete bottom formwork. Before the steel bar binding, steel pipe scaffolds are erected on both sides and one side of the support beam. After the steel bar binding is formed, the steel pipe scaffolds are removed. The skeleton is placed on the bottom formwork. The crown beam, concrete support and concrete corner brace are erected with composite formwork. The support system is jointly stressed by using 50×80 wooden square timbers, 48×3.5 short steel pipes, M12 tie bolts and fasteners. The surface of the formwork is flat, the joints are tight, and there is no leakage of slurry. For those with uneven diameters and edges and local unevenness, they should be repaired and corrected in time, otherwise they cannot be used. The formwork is coated with release oil before formwork erection. The release oil adopts clear machine oil. The formwork support adopts steel pipes with a diameter of 48 mm and a length of 1.8 m, which are driven into the soil by more than or about 0.6 m, with a spacing of 80 cm and two longitudinal steel pipes connected. Before pouring, the position, elevation, cross-sectional dimensions of the formwork, and the stability and joint conditions of the formwork and support are reviewed. The concrete adopts commercial concrete, and the commercial concrete is transported to the site by a drum-type transport vehicle with a capacity of 6 cubic meters or 8 cubic meters and pumped to each pouring point by a truck pump or a stationary pump. The truck pump selects a concrete pump truck with a wall length of 21 m. The truck pump or the stationary pump is parked on the construction access road for pumping. The formwork of the crown beam, concrete support and concrete corner brace is removed when the concrete strength can ensure that the surface and edges and corners are not damaged due to formwork removal after the concrete final setting. The concrete is cured by watering and moisturizing, and the surface is covered with burlap. The production water of the construction site water supply system is used, and the curing time is 7 days. After the concrete strength of the crown beam, concrete support and concrete corner brace reaches 95%, the lower layer of earthwork excavation is carried out; the demolition method of the foundation pit concrete support is to break it by mechanical cutting. The demolition sequence of the support is to first demolish the secondary support, and then demolish the opposite support. When demolishing the support beam, the connecting rod is demolished first and then the main support. When demolishing each support beam, cutting starts from the middle. The demolition of the support strengthens the protection of the wall panel to prevent the support beam from damaging the roof of the tunnel main structure. Protection measures such as laying wooden square timbers on the roof are taken;

[0030] In the above step 5, for the construction of the main structure, first, construction preparation work is carried out. After the foundation pit is excavated to the designed elevation, foundation pit inspection is carried out, and structural surveying and lofting are carried out; then the plain cushion layer construction is carried out. The cushion layer concrete is C20 and 20 cm thick. The cushion layer construction is carried out after the excavation surface. Drain the accumulated water in the foundation pit, remove the loose soil in the foundation pit, clean and level the top of the anti-pull pile, and remove the silt and other sundries. After the foundation pit is cleaned, use a rammer to tamp the foundation base and measure the bearing capacity of the foundation. When paving the cushion layer concrete, control the surface elevation according to the pre-buried level piles. The concrete is vibrated with a flat vibrator. After the cushion layer concrete begins to set and before it finally sets, perform secondary surface finishing on the surface layer and fully cure it to prevent looseness, sanding, and peeling. Control the pouring thickness of the cushion layer according to the pre-buried elevation control piles, and finish the surface and cure it to make the cushion layer surface free of honeycombs, pitted surfaces, and cracks; then carry out the support layout. The support for the main structure frame concrete construction is a full hall disc buckle support. Each disc buckle vertical pole in the full hall disc buckle support can bear a vertical load of 8 to 9 tons. The vertical load includes the side pressure of the side wall concrete, the weight of the top plate concrete, the weight of the formwork, the construction load, and the wind force acting on the formwork support. The longitudinal and transverse spacing of the disc buckle support is 60 cm and 90 cm, and the transverse spacing of the disc buckle support adjacent to the upper chamfer is 60 cm; then carry out the formwork construction. The external formwork for the concrete project uses the side wall of the enclosure structure. Before the side wall construction, first trim the wall surface of the enclosure structure flat. The formwork consists of a bottom formwork, a side wall formwork, and a top formwork, which are assembled on-site. The construction formwork for the bottom plate and a section of the side wall uses large steel formwork, which is processed into a frame with angle steel and channel steel, and the plywood is connected to the frame as a whole and processed into blocks for on-site assembly. The formwork uses 2440 mm × 1220 mm × 15 mm plywood as the panel, 60 mm × 80 mm square wood as the secondary joist, and φ48*3.5 mm steel pipe as the main joist. The outer side wall is poured up to 30 cm above the bottom plate axil angle during the bottom plate concrete pouring. Two rows of vertical embedded screws are arranged on the outer side wall. The upper row is a tie screw, and the lower row of embedded screws is welded to the main reinforcement of the structure and does not penetrate the entire bottom plate to prevent the formwork from moving. The longitudinal spacing of the screws is 600 mm, and the vertical spacing is 500 mm. The secondary joist uses 60 mm * 80 mm square wood, the main joist steel pipe is arranged vertically, and a steel pipe tie is set at the top. The side wall formwork system for the main structure in the open-cut section adopts single-sided formwork and uses a steel triangular truss and embedded parts as the formwork support system to fix the formwork firmly. The formwork panel is 4.5 m × 1.5m×5mm integral large steel formwork, with 75mm×8mm steel plates for the peripheral ribs, 75mm×50mm angle steel for the vertical secondary ribs, and 70mm×6mm steel plates for transverse connection. The spacing of the secondary back ribs is less than 300mm. The main back ribs on the vertical ribs are 10# double channel steels welded to the back ribs. The support adopts double 14# channel steel triangular frames with a spacing of 750mm. For the formwork system of the main structure roof slab in the open cut section, steel pipe scaffolds, adjustable supports, secondary rib square timbers, and main rib steel pipes are used for support. The formwork uses 2440mm×1220mm×15mm plywood as the panel, with two forms of secondary ribs: 8*8cm square timbers @30cm and double-ply Φ48 steel pipes @30cm, and 10# I-beams @80cm as the main ribs. A full hall scaffold is erected with a disc buckle support. According to the two forms of disc buckle supports, 48 and 60, the transverse spacing of the support is 90cm, and the longitudinal spacings are 60cm, 90cm, and 120cm, and the erection step distance is 1.5m. The cut edges of the formwork are protected with edge-sealing paint, and the wooden formwork is processed on-site at the construction site. Bottom ribs are provided at the formwork joints of the roof slab, and sponge strips are added to seal the vertical formwork joints. Cleaning ports are set at the roof slab and the ends. Before pouring concrete, a dust collector is configured to clean the sundries in the formwork. Thin sponge pads are embedded or putty is applied at the joints to eliminate the gaps. Before erecting the formwork, the formwork is polished, rust-removed, oiled, and trial-assembled. When erecting the formwork, the embedded parts are installed and fixed. The formwork release agent uses clean machine oil or release agent. The exposed length of the adjustable screw rod does not exceed 2 / 3 of the total length of the screw rod. Before the formwork enters the site, the formwork and the usage parts are numbered, and the formwork is arranged to enter the site in batches in an orderly manner to meet the on-site construction requirements and avoid occupying more space on-site. After the base waterproof coating construction meets the requirements, the bottom slab steel bars are tied. The side wall and roof slab steel bars are tied after the bottom slab concrete construction is completed and the inner formwork and bottom formwork are installed, and various joint bars are reserved according to the design. Subsequently, concrete pouring is carried out. First, the bottom slab concrete is poured. The concrete pouring adopts the inclined layer method and reaches the top at one time. The thickness range of each layer is 30cm to 40cm. The concrete pump truck starts pouring from the four corners on both sides of the foundation pit, allowing the concrete to flow naturally to form an inclined plane. Then, the middle partition wall and the outer side wall concrete are poured. For the tunnel concrete structure, the middle partition wall is poured first, and then the outer side wall is poured. The inclined layer construction method is adopted to control the one-time pouring height, achieving layered feeding and layered ramming, and advancing in a cyclic and integral manner. The thickness of each layer is 30cm. Two concrete pump trucks are used for simultaneous pouring, and the two side walls and the middle wall on both sides of the frame are poured symmetrically at the same time. Then, the roof slab concrete is poured. The concrete pouring adopts the inclined layer method and reaches the top at one time. The thickness range of each layer is 30cm to 40cm. The concrete pump truck starts pouring from the four corners on both sides of the foundation pit, allowing the concrete to flow naturally to form a certain inclined plane. Then, concrete vibration is carried out. The concrete is vibrated with internal vibrators. The moving distance of the vibrator does not exceed 1 times the action radius of the vibrator.By 5 times and insert it 5 cm to 10 cm into the lower layer of concrete. Compact the concrete thoroughly without vibration omission, under-vibration or over-vibration. Adopt the method of fast insertion and slow extraction, and arrange the vibration points evenly. Strengthen the vibration at the construction joints and embedded parts. During vibration, do not touch the formwork, steel bars, waterstop belts, and the bottom and top plates. After the top plate concrete is vibrated thoroughly, level, compact and polish the surface mortar before final setting. If the water content on the vibration surface is greater than the preset amount, use a vacuum pump and connect a 15-square-meter vacuum suction pad to suck away the accumulated water on the concrete surface area. Then carry out the maintenance of the concrete. After the concrete pouring is completed and initial setting occurs, sprinkle water for maintenance to ensure that the concrete surface is in a wet state. At the same time, cover the geotextile on the concrete surface; carry out the tunnel waterproof construction. First, determine the self-waterproofing of the concrete structure. The waterproof concrete is prepared by adjusting the mix ratio and adding admixtures and blending materials. Determine the anti-seepage grade of the structural concrete, the water-binder ratio of the structural concrete, and the minimum dosage of the binder material according to the strength of the concrete structure and the depth of the structure embedding. The top plate concrete and the side wall concrete poured together with the top plate adopt the addition of an appropriate amount of high-quality fly ash and slag to reduce dry shrinkage and temperature difference shrinkage; then carry out the waterproof coiled material construction. The side wall adopts a 1.5-mm-thick pre-laid polymer waterproof coiled material, the bottom plate adopts a 1.5-mm-thick pre-laid polymer coiled material, and the top plate adopts a flexible waterproof layer. The waterproof construction progress is consistent with the main structure construction progress. For each construction flow section, the waterproof coiled material construction of the bottom plate is carried out after the foundation pit excavation cushion layer is completed. The waterproof coiled material construction of the bottom plate for each flow section is controlled to be completed within 2 working days. The pre-laid polymer waterproof coiled material construction of the side wall is completed before the tunnel side wall construction. Each flow section is completed within 5 days. The one-component polyurethane waterproof coating on the top plate is completed within 2 working days after the top plate construction is completed and conditions are met. The 7-cm-thick C20 fine aggregate concrete protective layer is constructed after the waterproof coiled material construction is completed.

[0031] In step six above, carry out the earth backfilling. Spread the earth with a bulldozer, and the layer thickness is not more than 30 cm. Backfill on both sides of the tunnel frame according to the backfilling construction of the bridge culvert back. Compact with a rammer with an impact force range of 1 ton to 3 tons. The top plate filling is carried out according to the upper bridge filling process. Use a roller to statically press within 50 cm of the top plate. For a thickness greater than 50 cm, use a dump truck with a loading range of 10 tons to 15 tons to load the soil, and cooperate with a grader to spread and level it with a bulldozer, and vibrate and roll with a roller. The compactness is not less than 95%. After filling one layer, continue to fill and carry out the next process construction. Then carry out the construction of the anti-collision wall on the open section top. When constructing the bottom plate, orderly embed multiple iron parts, and these multiple iron parts are used to reinforce and support the U-shaped retaining wall concrete and the anti-collision wall. The anti-collision wall on the top of the open section retaining wall is constructed after the retaining wall concrete reaches the preset strength. The formwork erection and concrete pouring of the open section retaining wall and the anti-collision wall are the same as those of the tunnel main structure.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: the method for constructing an open-cut tunnel group in an ecologically sensitive area first determines an open-cut tunnel as the first construction section of the tunnel group during the construction confirmation stage, and then starts construction of other open-cut tunnels in sequence according to the progress of pipeline relocation. The tunnels are constructed in parallel, and each tunnel is divided into a number of foundation pits according to design requirements. Two working faces are set up in each foundation pit, and a flow operation rhythm is formed between each process, forming a competition between working faces, formulating a reward and punishment incentive mechanism, and establishing a typical mechanism. Under the premise of ensuring the safety of the project, the construction of multiple tunnels is carried out at the same time, and the implementation of a standardized construction site and the timely and punctual realization of the construction progress goals are ensured, thereby improving the construction efficiency; by carrying out The dewatering and drainage construction of the foundation pit is carried out. Among them, the dewatering construction of the foundation pit first involves drilling the dewatering well, measuring and locating the well point, digging the wellhead, installing the casing, positioning the drilling rig, drilling, cleaning the hole, hanging the well pipe, backfilling the filter layer between the well pipe and the hole wall, washing the well, installing a water pump in the well pipe, installing the pumping control circuit, test pumping, the normal operation of the dewatering well, pulling out the well pipe after dewatering, and sealing the well. The dewatering test is carried out before construction, and the layout, number, structural dewatering indicators, dewatering monitoring and other contents of the dewatering well points are adjusted to achieve the dewatering effect and ensure the safety of the foundation pit project, and better control the deformation of the foundation outside the pit to ensure the safety of surrounding pipelines and buildings. After the dewatering well is constructed, one well is put into operation. In order to lower the groundwater level in time and maintain all-weather operation, the foundation pit excavation should be carried out two weeks after the pre-precipitation. After the pressure reduction well is completed, an overall depth reduction and pumping should be carried out to verify whether it can meet the design requirements. When the foundation pit is excavated to the base, except for the reserved drainage outlet, the remaining pipe wells are immediately backfilled after being pulled out, and a cushion layer is applied. First, use a large-capacity water pump to pump water, and then use coarse sand to backfill the pipe well to the bottom elevation of the cushion layer. Use concrete of the same grade as the cushion layer to fill the well pipe, and carry out tunnel waterproofing construction, design concrete structure self-waterproofing and waterproof membrane construction, and effectively ensure the construction quality of the main structure of the tunnel; by taking the following auxiliary or remedial measures: First, establish a dynamic groundwater monitoring network along the line, and use the spare wells outside the pit to serve as observation Well logging, observing daily monitoring data of groundwater level, monthly monitoring data of groundwater quality, daily drainage data of foundation pit, drainage sand content data, etc.; secondly, establishing a settlement monitoring network. Before the implementation of the precipitation project, settlement monitoring points should be arranged according to the pumping influence range calculated in the precipitation design and the buildings within the range. Continuous settlement monitoring should be carried out during the pumping period. If the accumulated settlement is close to the warning value, necessary measures should be taken in time. If the settlement monitoring finds that the settlement of the building has reached a dangerous level, pumping must be stopped immediately to find out the specific cause of the settlement. When it is confirmed that it is caused by precipitation, recharging measures should be taken immediately. In the settlement area, the spare well outside the pit should be used for recharging. The distance between the recharging well and the precipitation well must be greater than 5.0 m, the specific design of the recharge well points should be determined according to the specific settlement conditions. Through the foundation pit deformation monitoring data under the condition of multi-warehouse excavation in the urban area, a set of advanced foundation pit safety management methods has been summarized. Brief Description of the Drawings

[0033] Figure 1 It is the flowchart of the method of the present invention. Detailed Embodiment

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0035] The applicant found the following problems in the existing technology: First, the existing urban tunnel construction is mainly the gradual construction of a single tunnel, and the construction efficiency is relatively low; Second, for the existing urban tunnel construction, there are relatively high requirements for the construction quality of the tunnel main structure; Third, for the existing urban tunnel construction, most of them do not utilize the foundation pit deformation monitoring data and lack a set of advanced foundation pit safety management methods; Therefore, it is very necessary to design a construction method for urban open-cut tunnel groups in ecologically sensitive areas.

[0036] A construction method for urban open-cut tunnel groups in ecologically sensitive areas provided by an embodiment of the present application can solve some of the problems existing in the above-mentioned existing technology.

[0037] Please refer to the attached Figure 1 , an embodiment provided by the present invention: A construction method for urban open-cut tunnel groups in ecologically sensitive areas includes the following steps: Step 1: Construction confirmation; Step 2: Retaining structure construction; Step 3: Foundation pit excavation; Step 4: Support construction; Step 5: Main body construction; Step 6: Auxiliary project construction;

[0038] In the first step above, confirm the construction sequence before and after the tunnel is constructed in sections and conduct corresponding traffic diversion. First, conduct an in-depth investigation of the urban planning and traffic demand in the ecologically sensitive area to understand factors such as the geographical location, surrounding environment, and traffic flow of the tunnel group. At the same time, analyze technical parameters such as the length, width, and burial depth of each tunnel to provide a basis for determining the construction sequence. Based on the investigation and analysis results, divide multiple tunnels into multiple construction sections. Each construction section may include one tunnel or a part of a tunnel. When dividing, factors such as the feasibility of construction technology, the balance of construction difficulty, and the convenience of traffic diversion need to be considered. Combining urban planning and traffic demand, follow the principle of "from easy to difficult, from the periphery to the interior" to determine the construction sequence of each open-cut tunnel and construction section, reducing the interference and impact on traffic. Exemplarily, since the method provided in the embodiment of the present application is applied to a tunnel group, and the tunnel group involves a large area, the geological conditions and the degree of impact on traffic are relatively complex. Therefore, it is difficult to determine the construction sequence of different construction sections in the prior art. In the method provided in the embodiment of the present application, each construction section in the tunnel group can be divided into a low-difficulty construction section, a medium-difficulty construction section, and a high-difficulty construction section. Among them, for any construction section in the tunnel group, if the construction section meets any three of the following four conditions: homogeneous hard rock, burial depth less than 50 meters, no groundwater, and a straight short tunnel (length less than 500 meters), then the construction section is determined as a low-difficulty construction section. If the construction section meets any three of the following four conditions: interbedded hard and soft rocks, local water seepage, curved tunnel, and burial depth less than 50 meters, then the construction section is determined as a medium-difficulty construction section. If the construction section meets any two of the following three conditions: water-rich fault, cross-section greater than 100 square meters, and burial depth greater than 500 meters, then the construction section is determined as a high-difficulty construction section. The construction sequence of the low-difficulty construction section can be arranged before the construction sequence of the medium-difficulty construction section, and the construction sequence of the medium-difficulty construction section can be arranged before the construction sequence of the high-difficulty construction section. Among them, a water-rich fault is a term in geology and tunnel engineering, referring to a special geological structure in the fault zone containing a large amount of groundwater, with high permeability and water storage capacity.

[0039] In addition, in an exemplary embodiment, difficulty weight values can be set for different conditions. The difficulty weight values for the three conditions of water-rich fault, cross-section greater than 100 square meters, and burial depth greater than 500 meters are 3. The difficulty weight values for the four conditions of interbedded hard and soft rocks, local water seepage, curved tunnel, and burial depth less than 50 meters are 2. The difficulty weight values for the four conditions of homogeneous hard rock, burial depth less than 50 meters, no groundwater, and straight short tunnel (length less than 500 meters) are 1. For any construction section in the tunnel group, it is possible to first determine that the construction section meets one or more of the above-mentioned multiple conditions, and then determine the total difficulty weight value of the construction section based on this one or these conditions. After that, based on the total difficulty weight values of each construction section, in ascending order of the total difficulty weight values, the construction order of each construction section is determined. That is, the smaller the total difficulty weight value, the earlier the construction order. When the total difficulty weight values of two construction sections are the same, it is possible to judge the number of the above-mentioned conditions with a difficulty weight value of 3 that are met in these two construction sections, and arrange the construction order of the construction section with a larger number of the above-mentioned conditions with a difficulty weight value of 3 after the construction order of the construction section with a smaller number of the above-mentioned conditions with a difficulty weight value of 3.

[0040] In an exemplary embodiment, for each construction section, it is possible to count the traffic flow of the adjacent roads (the adjacent roads can refer to the roads to be closed during the construction of the construction section) within a preset time period for this construction section, and then, in ascending order of the traffic volumes of these multiple construction sections, sort these construction sections, and this order is the construction order of these multiple construction sections.

[0041] Among them, the preset time periods for different construction sections can be different. Exemplarily, the preset time period can be positively correlated with the construction duration of the construction section. When the construction duration of the construction section is longer, the preset time period will also be longer, and the construction duration of the construction section can be determined based on the total difficulty weight value of the construction section. For example, when the total difficulty weight value is greater than 10, the preset time period of the construction section can be 10 days; when the total difficulty weight value is greater than 7 and less than or equal to 10, the preset time period of the construction section can be 7 days; when the total difficulty weight value is greater than 5 and less than or equal to 7, the preset time period of the construction section can be 5 days; when the total difficulty weight value is greater than 3 and less than or equal to 5, the preset time period of the construction section can be 3 days; when the total difficulty weight value is greater than 0 and less than or equal to 3, the preset time period of the construction section can be 1 day.

[0042] In an exemplary embodiment, influence weights can be set for each construction section based on the traffic flow of the road where each construction section is located. Among them, for each construction section, the traffic flow of the adjacent road in the preset construction period of this construction section can be counted. Then, based on the traffic volume of these construction sections from large to small, these construction sections are sorted. The influence weight of the construction sections ranked in the top 1 / 3 of the traffic flow ranking is set to 3, the weight of the construction sections ranked in the middle 1 / 3 of the traffic flow ranking is set to 2, and the weight of the construction sections ranked in the last 1 / 3 of the traffic flow ranking is set to 1. Then, the total difficulty weights of each construction section can be obtained in the above manner, and the total difficulty weight of this construction section is added to the influence weight to obtain the sequential weight. Then, according to the ascending order of the sequential weights, the construction order of each construction section can be determined. That is, the smaller the sequential weight, the earlier the construction order. In this way, the construction order of each construction section can be comprehensively determined by considering the construction difficulty and the impact on traffic. In this way, when there are a large number of construction sections in the tunnel group, the construction order of each construction section can be quickly determined.

[0043] During the construction period, temporary roads are set up to meet traffic needs. The setting of temporary roads should consider parameters such as the width, length, and traffic capacity of the roads to ensure smooth traffic. At the same time, obvious traffic signs and markings also need to be set up to guide vehicles and pedestrians to pass in an orderly manner. According to the traffic flow and road conditions during the construction period, the timing and phase of traffic lights are adjusted to improve the traffic capacity of the road. In addition, traffic warning signs and warning lights during the construction period also need to be set up to remind vehicles and pedestrians to pay attention to safety. Detailed traffic diversion measures are formulated, including traffic control during the construction period, the allocation of traffic diversion personnel, emergency traffic plans, etc., to ensure that during the construction period, the traffic order is in good order and the occurrence of traffic jams and traffic accidents is reduced; determine an open-cut tunnel as the first construction section of the tunnel group, and other open-cut tunnels start construction in sequence according to the progress of pipeline relocation. Each tunnel is constructed in parallel. Each tunnel is divided into several foundation pits according to the design requirements. 2 working faces are opened in each foundation pit, and a flow operation rhythm is formed between each process. Based on the construction progress of multiple working faces in multiple foundation pits, each working face is sorted, and the sorted information is transmitted to the terminals of each working face to form a competition between working faces, and a reward and punishment incentive mechanism and a typical model establishment mechanism are formulated.

[0044] In the second step mentioned above, for the construction of the retaining structure of the construction tunnel, the bored cast-in-place piles and secant bored piles are constructed first. For the bored piles, a full casing and a rotary drilling rig are used. The bored cast-in-place piles and high-pressure jet grouting piles form a water-stop curtain. The adjacent single piles of the secant bored piles are mutually occluded to form a pile wall. Among them, for the bored cast-in-place piles, a reinforced concrete guide wall needs to be constructed first above the pile top. The width of the guide wall is 3.5 m, the thickness is 35 cm, and the material is C25 concrete. Subsequently, the pile center position is accurately measured as the control point for the rig positioning. After the pile foundation is in place, first remove the obstacles at a soil depth of 2.5 - 3 m, then use a pile driver to sink the steel casing into the completely weathered rock layer, and check the verticality. If it is unqualified, rectify it; if it is qualified, take soil downward until the designed bottom elevation of the hole is reached. Subsequently, fabricate the steel cage and hoist it with a crane. The designed elevation can be deduced from the elevation of the top of the casing. During installation, it must be ensured that the elevation calculation is correct, and the allowable error is ±10 mm. When lowering the steel cage, it is manually assisted to align with the hole position, keeping it vertical, gently lowering it slowly, generally slowly sinking step by step by positive and reverse rotation to prevent collision. After reaching the designed elevation, it should be fixed immediately; when it is difficult to lower, stop immediately, find out the reason and deal with it. Subsequently, pour concrete. For the reinforced piles, underwater C35 concrete is used, and for the plain piles, super-retarding C35 concrete is used. The concrete pouring conduit is connected by a screw thread sleeve with a rubber sealing ring, with an inner diameter of 25 cm. After connection, check it in detail to ensure that the conduit is sealed and pressure-resistant, that is, conduct a sealing and pressure-resistant inspection after connection. If the conduit passes the sealing and pressure-resistant inspection, continue with the subsequent steps; if it fails the sealing and pressure-resistant inspection, remove the original connection, reconnect it with a screw thread sleeve with a rubber sealing ring, and conduct a sealing and pressure-resistant inspection again. Then, slowly lower the conduit into the hole with a crane. The bottom of the conduit should be 30 - 50 cm above the bottom of the hole to ensure the discharging space at the lower opening. The upper opening of the conduit is connected to a concrete funnel, and the upper opening of the conduit is sealed with a water-stop plug. The concrete flows into the funnel through a chute. When conditions are difficult, it can be hoisted into the funnel by a crane through a hopper. After storing more than 2 m³ of concrete in the funnel, pull out the bottom cover of the funnel, pour concrete into the conduit, and keep the concrete pouring continuously. After the pouring starts, it should be constructed compactly and continuously, and it is strictly prohibited to stop in the middle. During the pouring process, pay attention to the rise and fall of the water level in the hole. For example, a water level sensing device can be set in the hole to determine the rise and fall of the water level in the hole based on this water level sensing device, and measure the actual height of the concrete surface at any time and calculate the buried depth of the conduit to ensure that the bottom end of the conduit is buried 2 - 6 m below the concrete surface. The conduit should avoid being buried too deeply to cause difficulty in pulling out the pipe, and at the same time, the buried depth should not be too small to cause the steel cage to float or the conduit to be pulled out of the concrete surface resulting in a pile breaking accident. After the concrete pouring is completed, gradually remove the casing and the conduit. According to the buried depth of the conduit, remove 1 - 2 sections of the conduit each time. After the conduit is removed, it should be washed clean immediately for the next use; when lifting the casing, slowly pull it out and shake it left and right to enable the concrete to flow into the space occupied by the casing. At the same time, pay attention to observing whether the steel cage floats. The buried depth of the casing should be controlled at about 2 m. To ensure the quality of the concrete at the designed pile top, the concrete is poured 0.5 m above the pile top elevation, and this part of the concrete is chiseled off before constructing the capping beam.After the perfusion is completed, the casing and the conduit are pulled out. During the perfusion process, technical personnel are on duty throughout the whole process, and supervise the construction team to fill in the concrete perfusion record. The initial setting time of the plain concrete pile is determined according to the time required for a single pile to be formed. The time required for a single pile to be formed is directly related to geological conditions, pile length, pile diameter, and the capacity of the drilling rig, etc. Therefore, the initial setting time of the plain concrete pile can be determined according to the following method. First, measure the time t required for a single pile to be formed, and then calculate it according to the following formula: T = 3t + K, where: T = the initial setting time of the plain concrete pile, K = the reserve time, generally taking 1.5t, t = the time required for a single pile of A and B piles to be formed. During the hole-forming process, the verticality of the pile should be monitored and inspected. When the verticality of the pile does not reach the preset verticality, adjust the verticality of the pile so that the verticality of the pile reaches the preset verticality. During the pressing-down process of the casing, arrange 2 people to use plumb bobs to detect the verticality during the pressing-down process of the casing from two mutually perpendicular directions respectively. Or, the verticality during the pressing-down process of the casing can also be measured by a verticality sensor, and correct it at any time when deviation is found. For the construction of the high-pressure jet grouting pile, first level the site manually or mechanically, dig a sewage disposal pit and sewage drainage ditches, and make a slurry pool. According to the design requirements, mark the pile points clearly, use the self-walking of the drilling rig to move the drilling rig to the design hole position, adjust the verticality with a theodolite so that the drill bit aligns with the pile point. To prevent the drill pipe from tilting, the weight at the bottom of the drill pipe can be increased. Exemplarily, a counterweight block can be set at the position adjacent to the short rod and the drill bit to increase the weight at the bottom of the drill pipe through this counterweight block, so as to reduce the possibility of the drill pipe tilting, and check it at any time with a plumb bob during the drilling process. The inclination of the drill pipe is not greater than 0.5%, and the deviation between the drilling hole position and the design hole position is not greater than 50 mm. After the drilling rig is in place, first conduct a low-pressure water jetting test at 0.5 MPa to check whether the nozzle is unblocked and whether the pressure is normal. Move the debugged drilling rig to the design hole position, and adjust the verticality so that the drill bit aligns with the center of the design pile position. After the water jetting test, drilling can start. The purpose of increasing the water jetting pressure from 0.5 MPa to 1 MPa is to reduce friction and prevent the nozzle from being blocked. When the first drill pipe is drilled, stop the water jetting. After the pressure drops, connect the drill pipes and continue water jetting and drilling until the design pile bottom position is reached. Subsequently, use qualified 42.5 composite Portland cement and clean drinking water to prepare according to the selected mix ratio. The cement content is not less than 25%. According to the determined mix ratio, first add water into the bucket, then add cement, start the mixer to mix, flow through a filter screen into the slurry pool, and then pump it into the second filter screen with a slurry pump. After the second filtration, the slurry flowing into the slurry bucket is pressurized by a high-pressure pump and sent to the drilling rig through a high-pressure pipe for jet grouting. Among them, the slurry pressure is greater than 3 MPa, the water pressure is 25 MPa, the water-cement ratio of the slurry is 0.8, the rotation speed is generally preferably 10 r / min, and the lifting speed is 10 cm / min. After drilling to the design elevation, unscrew the upper drill pipe, put in a steel ball to block the water jetting hole, and then install the drill pipe, and then high-pressure cement slurry can be sent to the drilling rig. After the slurry gushes out from the bottom of the hole, the drill pipe starts to rotate and lift, and jet grouting is carried out from bottom to top.During the jet grouting process, the slurry overflow should be controlled within 10 - 25%. When encountering special soil layers such as gravel soil, etc., in order to ensure the pile diameter and quality, double jet grouting must be carried out. The double jet grouting height should not be less than 500 mm. During the rotation process, when the first drill pipe is lifted out of the ground, stop grouting. After the pressure drops, quickly remove the drill pipe. When it is lifted to the designed elevation of the pile top, start the jet grouting pile again. When it is lifted to the designed elevation of the pile top, to avoid the shrinkage of the slurry due to the removal of the slurry after mixing with the soil in the mixer, resulting in a concave cavity at the top of the jet grouting pile, carry out low-pressure supplementary jet grouting. After the supplementary jet grouting is completed, lift out the drill pipe and the drill bit and carry out low-pressure water jetting to wash the drill pipe and the nozzle, then the drilling rig can be moved. When encountering special situations, all pipelines and tools must be cleaned. After one pile is jet grouted, the drilling rig can be moved to carry out the operation of the next pile. The construction interval between adjacent two piles should not be less than 2 days, and the spacing should not be less than 2 m. Carry out the dewatering and drainage construction of the foundation pit. For the dewatering construction of the foundation pit, first carry out the hole forming of the dewatering well, and carry out the construction process flow of well point measurement and positioning, excavation of the wellhead, installation of the casing, positioning of the drilling rig, drilling, hole cleaning, lowering of the well pipe, backfilling of the filter layer between the well pipe and the hole wall, well washing, installation of the water pump in the well pipe, installation of the pumping control circuit, trial pumping, normal operation of the dewatering well, pulling out the well pipe after dewatering to sealing the well. Before construction, carry out a dewatering test, and adjust various contents such as the layout, quantity, structure, dewatering index, and dewatering monitoring of the dewatering well points, so as to achieve both the dewatering effect, ensure the safety of the foundation pit project, and better control the deformation of the foundation outside the pit to ensure the safety of the surrounding pipelines and buildings. After one dewatering well is constructed, it should be put into operation immediately to lower the groundwater level in time and keep running all day long. The foundation pit excavation should be carried out two weeks after pre-dewatering. After the construction of the depressurization well is completed, a whole drawdown pumping should be carried out to verify whether it can meet the design requirements. When the foundation pit is excavated to the base, except for the reserved drainage outlets, the remaining pipe wells should be pulled out and immediately backfilled, and the cushion layer should be constructed. First, pump a large amount of water with a water pump, and then backfill the pipe wells with coarse sand to the elevation of the bottom of the cushion layer, and fill the well pipe with concrete of the same grade as the cushion layer; at the same time, take the following auxiliary or remedial measures: First, establish a dynamic monitoring network for groundwater along the line, and use the standby wells outside the pit as observation wells to observe the daily monitoring data of the groundwater level, the monthly monitoring data of the groundwater quality, the daily drainage volume data of the foundation pit, the sand content data of the drainage water, etc.; Second, establish a settlement monitoring network. Before the implementation of the dewatering project, according to the pumping influence range calculated in the dewatering design and the buildings within this range, set up settlement monitoring points. During the pumping period, continuous settlement monitoring should be carried out. If the cumulative settlement amount is close to the warning value, take necessary measures in time. If it is found through settlement monitoring that the settlement of the building has reached a dangerous level, the pumping must be stopped immediately, find out the specific reasons for the settlement, and when it is confirmed that it is caused by dewatering, immediately take the recharging measure, and carry out recharging in the settlement area using the standby wells outside the pit. The distance between the recharge well and the dewatering well must be > 5.0 m, and the specific design of the recharge well point should be determined according to the specific settlement situation; then carry out the drainage construction of the foundation pit, and set up drainage ditches around or in the middle of the excavated foundation pit.A sump well is set every 15m to allow the seepage water and construction wastewater in the foundation pit to flow into it. Then, it is pumped into the surface sedimentation tank by a water pump and discharged to the municipal pipe network after treatment such as sedimentation. The drainage ditch and sump well are deepened while excavating, keeping the bottom of the ditch not less than 0.5m lower than the bottom of the foundation pit, and the sump well not less than 0.5m lower than the bottom of the ditch. A brick drainage ditch with a size of 400mm×400mm is set on the ground around the foundation pit, and a sedimentation tank with a size of 1000mm×500mm×500mm is set every 20m. During the excavation process, the groundwater in the pit is kept lowered to ensure that the groundwater is more than 1m below the excavation surface. The dewatering time lasts until the topsoil covering is completed. The dewatering of the foundation pit is carried out 15 to 20 days before the earthwork excavation, and the trial dewatering work is done well. When excavating to the construction bottom slab, temporary drainage holes are set on the bottom slab and sealed after the topsoil covering and the internal paving layer construction are completed. Dewatering outside the foundation pit is carried out 7 to 10 days before the foundation pit excavation, and the water level is lowered to 5m below the ground surface. One drainage hole is arranged every 200㎡.

[0045] In the above step three, the tunnel foundation pit is excavated, and the foundation pit excavation and support erection construction are carried out. During the foundation pit excavation and support, the earthwork excavation should follow the principles of zoning, block division, symmetry, balance, and time limit. The overall layer-by-layer or step-by-step layer-by-layer excavation method can be adopted, with the layer thickness not greater than 2m. During the excavation process, the temporary slope on the excavation surface is not greater than 1:1.5, and the unsupported exposure time is shortened as much as possible to effectively control the deformation of the support structure. The "time-space effect" theory principle is used to excavate the foundation pit. It should be excavated layer by layer, and the next layer is excavated after the support is completed. Overexcavation is strictly prohibited. When approaching the base, follow the principles of rapid excavation and rapid bottom sealing, do a good job in controlling the key processes and preventive measures during the foundation pit excavation, formulate the construction organization design and construction operation procedures, fully prepare the drainage equipment for removing the accumulated water in the foundation pit, effectively prepare the conditions for soil excavation, transportation, and soil disposal, and protect all types of monitoring points, and do a good job in the monitoring of the initial readings. Only after the initial readings are available can the excavation be carried out, and the monitoring work should be done according to the frequency required by the design, and the observation should be intensified according to the actual situation on site to analyze the stability of the foundation pit based on the dynamic situation; during the excavation process, if there is a leakage phenomenon on the retaining wall, it should be blocked in time to prevent small amounts of quicksand from breaking through the support, resulting in soil erosion, which will not only cause a large amount of ground settlement, but also lead to the instability of the support structure, resulting in serious disastrous accidents; to make the bottom of the pit flat and prevent local overexcavation, the soil within 30cm above the designed bottom elevation of the pit should be excavated and leveled manually, and the local excavated depressions should be filled with sand. At the same time, sump wells must be set to pump out the accumulated water at the bottom of the pit;

[0046] In the above step 4, for the construction support structure project, the construction of the reinforced concrete capping beam and the reinforced concrete support beam is carried out. The technological process is the leveling, compaction, measurement and setting out, laying of bitumen felt isolation layer, steel bar binding, formwork installation, acceptance of steel bars and formwork, concrete pouring and curing of the soil under the support beam. Before the construction of the retaining piles, the concrete guide wall is set up first. The outer guide wall is used as the retaining wall for excavation. Therefore, attention should be paid to protecting the integrity of the outer guide wall during construction. After the construction of the retaining pile retaining structure is completed, the inner guide wall is demolished and loaded and transported out together with the soil. The concrete debris, soil and impurities within the range of the wall top are cleaned and removed by manual labor and air compressor, and then washed clean with high-pressure water; the construction methods of each process of the reinforced concrete collar beam and the reinforced concrete support are carried out layer by layer and section by section according to the aforementioned construction methods of foundation pit excavation and support for the excavation of the upper first layer of soil and the construction of the first reinforced concrete collar beam and support. According to the design elevation, the positions of each reinforced concrete collar beam and support are set out by using a level and based on the foundation pit retaining wall. And the base is cleaned manually to ensure the level of the foundation pit bottom. The bottom formwork of the support is made of C20 concrete, with a thickness of 15 cm and a width 15 cm wider than the width of the support beam. After the earthwork excavation and leveling are completed, the base is tamped, leveled with gravel, and the two sides are provided with 4-cm-thick shaped wooden formwork. The concrete is poured and vibrated solid with a flat vibrator. After the surface is pressed twice with wooden wedges, it is polished with an iron plate. After the pouring of the concrete bottom formwork is completed, it must be covered with straw bags and watered for curing for 3 days. The steel bars can be bound only after the strength of the concrete bottom formwork reaches 50%. A layer of isolation layer must be set on the surface of the concrete bottom formwork. Before the steel bars are bound, steel pipe supports are erected on both sides and one side of the support beam. After the steel bars are bound and formed, the steel pipe supports are removed. The framework is placed on the bottom formwork. The capping beam, concrete support and concrete corner brace are set up with composite formwork. The support system is jointly stressed by using 50×80 wooden squares, 48×3.5 short steel pipes, M12 tie bolts and fasteners. The surface of the formwork must be flat, the joints must be tight and there must be no leakage of slurry. For those with uneven diameters and edges and local unevenness, they should be repaired and corrected in time, otherwise they cannot be used. The formwork must be coated with release oil before formwork erection. The release oil used is clear machine oil. The formwork support is made of Φ48 steel pipes, with a length of 1.8 m, and driven into the soil not less than 0.6m, with a spacing of 80 cm and longitudinally connected by 2 steel pipes. Before pouring, the position, elevation, cross-sectional dimensions of the formwork, as well as the stability and joint conditions of the formwork and supports should be rechecked or inspected. The concrete used is commercial concrete, which is transported to the site by a drum-type transport vehicle with a capacity of 6 m3 or 8 m3, and then conveyed to each pouring point by a truck pump or a stationary pump. The truck pump selected is a concrete pump truck with a boom length of 21 m. The truck pump or stationary pump is parked on the construction access road for pumping. For the removal of the formwork of the capping beam, concrete support, and concrete corner brace, generally, when the concrete strength can ensure that its surface and edges are not damaged due to formwork removal after the concrete has set, the formwork can be removed. The formwork removal should not be pried forcefully to avoid damage to the corners. The concrete is cured by watering and moisturizing, with a burlap covering on the surface, and the production water from the construction site water supply system is used. The curing time is generally 7 days. Attention should be paid to the protection of the finished products. The capping beam, concrete support, and concrete corner brace can be loaded when the concrete strength reaches 95%, and then the lower layer of earthwork excavation can be carried out; the method for removing the concrete support in the foundation pit is to break it by mechanical cutting. The order of support removal is to first remove the secondary support and then the opposite strut. When removing the support beam, the connecting rod should be removed first and then the main strut. When removing each support beam, cutting should start from the middle. During the support removal, the protection of the wall panel should be strengthened to prevent the support beam from damaging the roof slab of the tunnel main structure. Protective measures such as laying wooden squares on the roof slab can be taken. The construction waste after removal should be promptly removed manually;.

[0047] In the above step five, the main structure of the tunnel is constructed. For the main structure construction, the construction preparation work is carried out first. After the foundation pit is excavated to the designed elevation, the trench is inspected as soon as possible, and the structure is measured and laid out. The formwork support system of the side wall and the top plate is designed and calculated, and a special plan for tunnel formwork is prepared. After being submitted to experts for demonstration and improvement and approval, the plan is organized for implementation. The material feed is arranged in advance according to the construction progress, and the structural construction sequence, construction progress schedule, construction methods and technical requirements are carefully explained to the work team and all management personnel; then the plain cushion layer is constructed. The cushion layer concrete is C20, 20cm thick, and the cushion layer construction is carried out closely following the excavation surface to prevent the base from being exposed for too long, eliminate water accumulation in the foundation pit, remove the loose soil in the foundation pit, clean and level the top of the pull-out piles, silt and other debris. After the foundation pit is cleaned, the base is fully compacted with a tamping machine, and the bearing capacity of the foundation is measured, and the owner and engineer are reported in writing in a timely manner. When the cushion layer concrete is spread, according to the pre-buried water The elevation of the surface layer is controlled by flat piles, and the concrete is tamped with a flat vibrator. After the initial setting and before the final setting of the cushion concrete, the surface layer is calendered for the second time and fully cured to prevent looseness, sand and peeling. The thickness of the cushion layer is controlled by the pre-buried elevation control piles, and the surface is closed and cured in time to ensure that there are no honeycombs, pits and cracks on the cushion surface. Then the bracket is arranged. The bracket used for the main structure frame concrete construction is a disc-type full-floor bracket. The bracket is arranged through calculation to ensure that the strength and stiffness meet the construction requirements. It is considered that each disc-type vertical pole can withstand 8 to 9 tons of vertical load. The calculation takes into account the side wall concrete pressure, the weight of the top plate concrete, the weight of the formwork, the construction load, the wind force acting on the formwork bracket and other possible loads. Therefore, the longitudinal and transverse spacing of the disc-type bracket is 60cm and 90cm, and it is encrypted to 60cm near the upper chamfer to strengthen the stiffness of the longitudinal and transverse beams of the top plate and the transverse and vertical belts of the side walls. The disc-type bracket has the characteristics of flexible disassembly, and no unloading device is provided during construction.Then carry out formwork construction. The external formwork for the concrete project utilizes the side walls of the retaining structure. Before constructing the side walls, the walls of the retaining structure should first be trimmed and leveled. The formwork consists of three parts: the bottom formwork, the side walls, and the top formwork, which are assembled on-site. The construction formwork for the bottom slab and a section of the side walls uses large steel formwork, which is processed into a frame with angle steel and channel steel, and the plywood board is connected to the frame to form a whole, and is processed into large blocks according to the design drawings and assembled on-site. Considering reuse, the formwork uses 2440×1220×15 plywood as the formwork surface, 60mm×80mm square timbers as the secondary ribs, and φ48*3.5mm steel pipes as the main ribs. The outer side wall needs to be poured up to 30 cm above the bottom slab axil angle during the pouring of the bottom slab concrete. There are 2 rows of vertical embedded bolts on the outer side wall. The upper row is the tie bolt, and the lower row of embedded bolts is welded to the main reinforcement of the structure and does not penetrate the entire bottom slab to prevent the movement of the formwork. The longitudinal spacing of the bolts is 600 mm, and the vertical spacing is 500 mm. The special-shaped steel formwork is used for the inner chamfer part of the side wall, the secondary ribs use 60*80 square timbers, the main ribs are arranged vertically, and a steel pipe tie is set at the top. The side wall formwork system of the main structure in the open-cut section mainly uses single-sided formwork, mainly using the steel triangular truss and embedded parts as the support system of the formwork to fix the formwork firmly. The formwork surface uses a 4.5m×1.5m×5mm integral large steel formwork. The four-sided ribs are 75*8 steel plates, the vertical secondary ribs are 75*50 angle steels, and the transverse is connected with 70*6 steel plates. The spacing of the secondary back ribs is less than 300 mm. The main back ribs on the vertical ribs are 10# double channel steels ("10" represents the waist height of 100 mm, and the cross-sectional dimensions of 10# channel steel are 100mm (waist height) × 48mm (leg width) × 5.3mm (waist thickness)) welded to the back ribs to increase strength. The support uses double 14# channel steel triangular frames with a spacing of 750 mm. The top slab formwork system of the main structure in the open-cut section uses steel pipe scaffolds + adjustable supports + secondary rib square timbers + main rib steel pipes for support. The formwork uses 2440×1220×15mm plywood as the formwork surface, and two forms of secondary ribs are used: 8*8cm square timbers @30cm and double Φ48 steel pipes @30cm. 10# I-beams @80cm (10# indicates that the model of the I-beam is No. 10. The height of the No. 10 I-beam is 100 mm, the leg width is 68 mm, the waist thickness is 4.5 mm, and the theoretical weight is 11.2 kg / m. @80cm means that the center spacing of two adjacent I-beams is 80 cm) are used as the main ribs. The full hall scaffold is supported by the disc buckle type scaffold. According to the two forms of disc buckle scaffolds of 48 and 60, the transverse spacing of the scaffold is 90 cm, and the longitudinal spacing is 60 cm, 90 cm, and 120 cm. The erection step distance is 1.5 m. The cut edges of the formwork are protected with edge-sealing paint to reduce the generation of burrs again at the cut edges or water swelling and loose deformation. All materials entering the site should have quality certificates and test reports. The wooden formwork is processed on-site at the construction site. The carpentry processing team accurately arranges the formwork according to the drawings. After processing and forming, first, the processing team conducts self-inspection and rectifies problems in a timely manner; then, the quality inspector conducts special inspection on the processing to control the allowable deviation of the formwork processing within the specified range;Before use, the installation team shall conduct a handover inspection on the wooden processed products again. Those that affect the use shall be immediately returned for renovation. Bottom bearers shall be set at the seams of the top plate formwork to minimize the use of plastic tape. Sponge strips shall be added to seal the seams of the vertical formwork. Cleaning ports shall be set at appropriate positions on the top plate and the ends. Before pouring concrete, a dust collector shall be configured to clean the sundries in the formwork. During construction, attention shall be paid to the appearance quality of the concrete. All joints shall be tight without leakage of mortar. When necessary, thin sponge pads shall be embedded at the joints or putty shall be applied to eliminate the gaps. Before form erection, the formwork shall be polished, rust removed, oiled and trial assembled. When erecting the formwork, all kinds of embedded parts shall be installed and fixed. The formwork release agent shall be clean engine oil or a reliable release agent with good quality. The form removal time shall be controlled, and specimens cured under the same conditions shall be reserved. Whether to remove the formwork shall be determined according to the requirements of the specifications. Special tools such as a flat spatula with a blade and a dry mop shall be used to clean the formwork. Hammering the formwork is prohibited. The release agent shall not be applied until the formwork is cleaned. The formwork that has not been cleaned, maintained and coated with the release agent cannot be used. The bottom tie rods and top tie rods of each vertical pole must be fully installed and ensure reliable connection. The exposed length of the adjustable screw rod does not exceed 2 / 3 of the total length of the screw rod. Before the formwork enters the site, according to the project arrangement and the division of the flowing water sections of the project department, the formwork shall be numbered and the using parts shall be numbered. The formwork shall be arranged to enter the site in batches in an orderly manner to meet the requirements of on-site construction and avoid occupying more space on the site. After the base waterproof coating is constructed to meet the requirements, the binding of the bottom plate steel bars shall be started. The steel bars of the side walls and the top plate shall be bound after the construction of the bottom plate concrete and the installation of the inner formwork and the bottom formwork, and various joint steel bars shall be reserved according to the design. All steel bars shall be subjected to various tests in advance according to the requirements of the specifications, arranged strictly according to the requirements of the design drawings and submitted to the engineer for approval. The binding and welding of the steel bars shall comply with the requirements of the construction specifications.Then the concrete is poured. Before pouring concrete, the concrete mix design and various material experiments are carefully done. Before concrete transportation, the equipment must be repaired to ensure that the machine is in good condition. The bottom slab concrete is poured first. The concrete pouring adopts the method of inclined layering and one-time to the top. The thickness of each layer is controlled at 30 to 40 cm. The pump truck starts pouring from the four corners on both sides of the foundation pit, allowing the concrete to flow naturally to form a certain slope, and then the middle partition wall and outer wall concrete pouring are carried out. For the tunnel concrete structure, the middle partition wall is poured first, and then the outer wall is poured. The "inclined layered construction method" is used to control the pouring height at one time, so that the material is discharged in layers, the layers are tamped, and the cycle is promoted as a whole. The thickness of each layer is preferably 30 cm. Two concrete pump trucks are used for pouring at the same time. The side walls and the middle wall on both sides of the frame are poured symmetrically at the same time. Then the top slab concrete is poured. The concrete pouring adopts The slope is layered and poured to the top at one time. The thickness of each layer is controlled at 30-40cm. The pump truck starts pouring from the four corners on both sides of the foundation pit, allowing the concrete to flow naturally to form a certain slope, and then the concrete is vibrated. The concrete is compacted by inserting vibration. The moving spacing of the vibrating rod shall not exceed 1.5 times its effective radius, and it shall be inserted into the lower concrete for 5-10cm. The concrete must be compacted without missing vibration, insufficient vibration, or excessive vibration. The fast insertion and slow withdrawal method shall be adopted, and the vibration points shall be evenly arranged. The construction joints and embedded parts shall be vibrated more. The formwork, steel bars, water stop strips, and bottom plates shall not be touched during vibration. After the top plate concrete is vibrated and compacted, the surface slurry shall be smoothed, compacted, and pressed before final setting to ensure that the concrete surface does not crack. If there is too much moisture on the vibrated surface, the surface vacuum pump shall be used to absorb water and apply pressure multiple times, that is, a vacuum pump is used to connect a 15m piece. 2The vacuum absorbent pad absorbs the water on the surface of the concrete to ensure that the concrete surface does not crack. Finally, the concrete is cured. After the concrete is poured and initially set, it is watered to ensure that the concrete surface is always moist. At the same time, a geotextile is covered on the concrete surface to continue to keep the material moist. The curing water and materials must not cause adverse effects on the appearance quality of the concrete. The curing time is determined based on the on-site measured atmospheric humidity and temperature. For tunnel waterproofing construction, the self-waterproofing of the concrete structure should be designed first. The waterproof concrete should be configured by adjusting the mix ratio and adding admixtures and admixtures. The structural concrete impermeability grade, structural concrete water-cement ratio, and minimum amount of cementitious materials should be determined based on factors such as the strength of the concrete structure and the depth of structural burial. The top slab concrete and the side wall concrete cast together with the top slab should be added with appropriate amounts of high-quality fly ash, slag and other active materials and other anti-seepage measures. Reduce shrinkage and temperature difference shrinkage. The self-waterproofing design of concrete structures should select appropriate materials according to the environmental conditions to meet the requirements of concrete's own impermeability, durability and crack resistance. Then carry out waterproofing membrane construction. The side wall / enclosure section uses 1.5mm thick pre-laid polymer waterproofing membrane, the bottom plate uses 1.5mm thick pre-laid polymer waterproofing membrane, and the top plate uses a flexible waterproof layer. The waterproofing construction progress is consistent with the main structure construction progress. After the foundation pit excavation cushion layer is completed, the bottom plate waterproofing membrane construction of each construction flow section is carried out. The construction of the bottom plate waterproofing membrane is controlled to be completed within 2 working days for each flow section. The construction of the side wall pre-laid polymer waterproofing membrane is completed before the construction of the tunnel side wall. Each flow section is completed within 5 days. The top plate single-component polyurethane waterproof coating is completed within 2 working days after the top plate construction is completed and the conditions are met. The 7cm thick C20 fine stone concrete protective layer is constructed immediately afterwards.

[0048] In Step 6 mentioned above, earthwork backfilling is carried out, and the remaining structural works are constructed. For earthwork backfilling, 5-8t dump trucks are used to transport the purchased earthwork to the construction site in the early stage of backfilling. Manual labor is combined with bulldozers for spreading, and the layer thickness is not more than 30cm. The backfilling on both sides of the tunnel frame is carried out according to the backfilling construction of the bridge abutment. A 1-3t rammer is used for compaction until the compactness meets the design requirements. The topsoil filling of the roof is carried out according to the upper soil filling process of the bridge. For the part within 50cm from the roof, static compaction is carried out with a roller. For the part more than 50cm thick, 10-15T dump trucks can be used to load the soil, and bulldozers are combined with graders for spreading and leveling. Vibration compaction is carried out with a roller, and the compactness is not less than 95%. After a layer is filled and inspected to meet the requirements, the filling can continue and the next process can be carried out. Subsequently, the anti-collision wall at the top of the open section is constructed. When constructing the floor slab, pay attention to embedding some iron parts in an orderly manner for the reinforcement support of the U-shaped retaining wall concrete and the anti-collision wall. The anti-collision wall at the top of the open section retaining wall is constructed immediately after the retaining wall concrete reaches a certain strength. The formwork erection and concrete pouring of the open section retaining wall and the anti-collision wall are the same as those of the tunnel main structure. First, the electrical installation works are carried out, including tunnel power supply and distribution, tunnel power distribution, tunnel lighting, lightning protection and grounding, and others, lighting for the pump house and auxiliary rooms, tunnel management center, computer network system, closed-circuit television monitoring system, traffic video monitoring, automatic control system for mechanical and electrical equipment, fire alarm and linkage control system, wired broadcast system, emergency telephone system, wireless communication system, UPS uninterruptible power supply system, and other comprehensive pipelines; then the installation and commissioning of tunnel fans and control boxes are carried out; finally, the decoration works, fire protection and landscape works are constructed.

[0049] Based on the above, the advantages of the present invention are as follows. When the present invention is in use, during the construction confirmation stage, a cut-and-cover tunnel is first determined as the first construction section of the tunnel group, and other cut-and-cover tunnels start construction in sequence according to the progress of pipeline relocation. Each tunnel is constructed in parallel. According to the design requirements, each tunnel is divided into several foundation pits, and 2 working faces are opened for each foundation pit. A flow operation rhythm is formed among each process, a competition between working faces is formed, a reward and punishment incentive mechanism and a model setting mechanism are formulated. On the premise of ensuring project safety, the construction of multiple tunnels is carried out simultaneously, and the implementation of a standardized construction site and the timely and punctual realization of the construction progress target are ensured, thus improving the construction efficiency; by carrying out the dewatering and drainage construction of the foundation pit, in which for the foundation pit dewatering construction, first the dewatering wells are drilled. The construction process flow includes well point measurement and positioning, excavation of the wellhead, installation of the casing, drilling rig in place, drilling, hole cleaning, lowering of the well pipe, backfilling of the filter layer between the well pipe and the hole wall, well washing, installation of the water pump in the well pipe, installation of the pumping control circuit, trial pumping, normal operation of the dewatering well, pulling out the well pipe after dewatering until well sealing. Before construction, a dewatering test is carried out to adjust various contents such as the layout, quantity, structure dewatering index, and dewatering monitoring of the dewatering well points, so as to achieve both the dewatering effect, ensure the safety of the foundation pit project, and better control the deformation of the foundation outside the pit, ensuring the safety of the surrounding pipelines and buildings. As soon as a dewatering well is constructed, it is put into operation immediately to timely lower the groundwater level and keep running around the clock. The foundation pit excavation should be carried out two weeks after pre-dewatering. After the construction of the depressurization well is completed, a whole-depth pumping test is required to verify whether it can meet the design requirements. When the foundation pit is excavated to the base, except for the reserved drainage outlets, the remaining pipe wells are immediately backfilled after being pulled out, and the cushion layer is constructed. First, a large-capacity water pump is used for pumping, and then the pipe wells are backfilled with coarse sand to the bottom elevation of the cushion layer, and the well pipes are filled with concrete of the same grade as the cushion layer. And through the tunnel waterproof construction, the self-waterproofing of the designed concrete structure and the waterproof coiled material construction are carried out, effectively ensuring the construction quality of the tunnel main structure; by taking the following auxiliary or remedial measures: First, establish a dynamic monitoring network for groundwater along the line, and use the standby wells outside the pit as observation wells to observe the daily monitoring data of the groundwater level, the monthly monitoring data of the groundwater quality, the daily drainage volume data of the foundation pit, the sand content data of the drainage water, etc.; Second, establish a settlement monitoring network. Before the implementation of the dewatering project, settlement monitoring points are arranged according to the pumping influence range calculated in the dewatering design and the buildings within this range. Continuous settlement monitoring should be carried out during pumping. If the cumulative settlement amount is close to the warning value, necessary measures should be taken in time. If it is found through settlement monitoring that the settlement of the building has reached a dangerous level, pumping must be stopped immediately, and the specific reasons for the settlement should be found out. When it is confirmed that it is caused by dewatering, a recharging measure should be taken immediately, and recharging is carried out using the standby wells outside the pit in the settlement area. The distance between the recharge well and the dewatering well must be >5.0 m. The specific design of the recharge well points should be determined according to the specific settlement situation. Through the foundation pit deformation monitoring data under the condition of multi-chamber excavation in the urban area, an advanced foundation pit safety management method has been summarized.

[0050] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, in any regard, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claims involved.

Claims

1. A construction method for an open-cut tunnel group in a city in an ecologically sensitive area, comprising the following steps: Step 1: Construction confirmation; Step 2: Enclosure construction; Step 3: Foundation pit excavation; Step 4: Support construction; Step 5: Main body construction; Step 6: Auxiliary project construction; It is characterized in that: In the above Step 1, confirm the construction sequence before and after tunnel section construction and conduct corresponding traffic guidance. In the above Step 2, construct the tunnel enclosure structure. In the above Step 3, conduct the excavation of the tunnel foundation pit. In the above Step 4, construct the support structure project. In the above Step 5, construct the main structure of the tunnel. In the above Step 6, backfill the soil and construct the remaining structure projects.

2. The construction method of an urban open-cut tunnel group in an ecologically sensitive area according to claim 1, characterized in that: In the above Step 1, obtain the geographical location, surrounding environment and traffic flow of the tunnel group, obtain the lengths, widths and burial depths of multiple tunnels in the tunnel group, divide the multiple tunnels in the tunnel group into multiple construction sections, and determine the construction sequence of each open-cut tunnel and construction section in the tunnel group; During the construction period, set up temporary roads, and traffic signs and markings for guiding vehicles and pedestrians to pass orderly are set on the temporary roads. According to the traffic flow and road conditions during the construction period, adjust the timing and phase of traffic lights to improve the traffic capacity of the road. In addition, set traffic warning signs and warning lights during the construction period; Determine an open-cut tunnel as the first construction section of the tunnel group, and other open-cut tunnels start construction in sequence according to the progress of pipeline relocation, and each tunnel constructs in parallel.

3. The construction method of an urban open-cut tunnel group in an ecologically sensitive area according to claim 1, characterized in that: In the second step, bored cast-in-place piles and secant bored piles are constructed first. For the bored piles, a full casing and a rotary drilling rig are used. The bored cast-in-place piles and high-pressure jet grouting piles form a cut-off curtain. The adjacent single piles of the secant bored piles are mutually interlocked to form a pile wall. Among them, for the bored cast-in-place piles, a reinforced concrete guide wall is first constructed above the pile top. The guide wall is 3.5 meters wide, 35 cm thick, and made of C25 concrete. Subsequently, the pile center position is accurately measured as the control point for the drilling rig positioning. After the pile foundation is in place, first remove obstacles at a soil depth of 2.5 meters to 3 meters, then use a pile driver to sink the steel casing to the completely weathered rock layer, and check whether the verticality reaches the preset verticality. If the preset verticality is not reached, correct the verticality deviation. If the preset verticality is reached, take soil downward until the designed bottom elevation of the hole is reached. Subsequently, fabricate the steel cage and use a crane to hoist it. The designed elevation is determined by the elevation of the casing top. When the steel cage is lowered, it is gradually lowered by positive rotation or reverse rotation to prevent collision. After being lowered to the designed elevation, it is fixed. Subsequently, pour concrete. For the reinforced piles, underwater C35 concrete is used, and for the plain piles, super-retarding C35 concrete is used. The concrete pouring conduit is connected by a screw thread sleeve and a rubber sealing ring, with an inner diameter of 25 cm. The conduit is lowered into the hole by a crane. The bottom of the conduit is 30 - 50 cm above the bottom of the hole to ensure the discharging space at the lower opening. The upper opening of the conduit is connected to a concrete funnel, and the upper opening of the conduit is sealed with a water-stop plug. The concrete flows into the funnel through a chute. After more than 2 cubic meters of concrete is stored in the funnel, pull out the bottom cover of the funnel, pour concrete into the conduit, and keep the concrete pouring continuously. After the pouring starts, continuous construction is carried out. During the pouring process, measure the actual height of the concrete surface and calculate the buried depth of the conduit so that the bottom end of the conduit is buried 2 meters to 6 meters below the concrete surface. After the concrete pouring is completed, gradually remove the casing and the conduit, remove 1 to 2 sections of the conduit each time, and wash the conduit after the conduit is removed. When the casing is lifted, lift the casing and shake it left and right so that the concrete can flow into the space occupied by the casing. The buried depth of the casing is controlled at about 2 meters. The concrete is poured to 0.5 meters above the pile top elevation, and this part of the concrete is chiseled off before constructing the capping beam. After the pouring is completed, pull out the casing and the conduit. The retardation time of the plain pile concrete is determined according to the single-pile construction time. The retardation time of the plain pile concrete can be determined according to the following method. First, measure the time t required for a single-pile construction, and then calculate it according to the following formula: T = 3t + K, where: T = the retardation time of the plain pile concrete, K = the reserve time, generally taking 1.5t, t = the single-pile construction time of pile A and the single-pile construction time of pile B. During the pressing-down process of the casing, use plumb bobs to detect the verticality of the casing pressing-down process from two mutually perpendicular directions respectively, and correct it at any time when deviation is found; Among them, for the construction of high-pressure jet grouting piles, first level the site, dig a sewage pool and sewage ditch, make a slurry pool, use obvious signs to mark the pile points, use the self-walking function of the drill rig to move the drill rig to the designed hole position, use a theodolite to adjust the verticality so that the drill bit aligns with the pile point, and use a plumb bob to check at any time during the drilling process. The inclination of the drill pipe is less than or equal to 0.5%, and the deviation between the drilled hole position and the designed hole position is less than or equal to 50 mm. After the drill rig is in place, first conduct a water jetting test at 0.5 MPa. Move the debugged drill rig to the designed hole position, adjust the verticality so that the drill bit aligns with the center of the designed pile position. After the water jetting test, start drilling. The water jetting pressure increases from 0.5 MPa to 1 MPa. When the first drill pipe is drilled, stop water jetting. After the pressure drops, connect the drill pipe and continue water jetting and drilling until the designed pile bottom position is reached. Subsequently, use 42.5 composite Portland cement and clean drinking water to prepare according to the preset mix ratio. The cement content is greater than or equal to 25%. According to the determined mix ratio, first add water to the bucket, then add cement, start the mixer to mix, flow through the filter screen into the slurry pool, and then use a slurry pump to pump it into the second filter screen. After the second filtration, the slurry flowing into the slurry bucket is pressurized by a high-pressure pump, sent through a high-pressure pipe to the drill rig for jet grouting. Among them, the slurry pressure is greater than 3 MPa, the water pressure is 25 MPa, the slurry water-cement ratio is 0.8, the rotation speed is 10 revolutions per minute, and the lifting speed is 10 cm per minute. After drilling to the designed elevation, unscrew the upper section of the drill pipe, put in a steel ball to block the water jetting hole, and then install the drill pipe. Then, send high-pressure cement slurry to the drill rig. After the slurry emerges from the bottom of the hole, the drill pipe starts to rotate and lift, and jet grouting is carried out from bottom to top. During the jet grouting process, the amount of bleeding is controlled within 10% - 25%. When encountering gravel soil, re-jet grouting is carried out, and the re-jet grouting height is greater than or equal to 500 mm. During the rotation process, when the first drill pipe is lifted out of the ground, stop grouting. After the pressure drops, remove the drill pipe. When the designed pile top elevation is reached, start jet grouting piles again. When the designed pile top elevation is reached, carry out low-pressure supplementary jet grouting. After the low-pressure supplementary jet grouting is completed, lift out the drill pipe and drill bit for low-pressure water jetting to wash the drill pipe and nozzle, and move the drill rig. After one pile is jet grouted, move the drill rig to carry out the operation of the next pile. The construction interval time between adjacent two piles is greater than or equal to 2 days, and the spacing is greater than or equal to 2 meters.

4. A construction method for an urban open-cut tunnel group in an ecologically sensitive area according to claim 1, characterized in that: In the second step, dewatering and drainage construction of the foundation pit is carried out. For the dewatering construction of the foundation pit, first, the dewatering wells are drilled. The construction process flow includes well point measurement and positioning, excavation of the wellhead, installation of the casing, rig positioning, drilling, hole cleaning, lowering of the well pipe, backfilling of the filter layer between the well pipe and the hole wall, well washing, installation of the water pump inside the well pipe, installation of the pumping control circuit, trial pumping, normal operation of the dewatering well, and pulling out the well pipe and sealing the well after dewatering is completed. Before construction, a dewatering test is carried out to adjust the layout, quantity, structure, dewatering index, and dewatering monitoring of the dewatering well points. As soon as a dewatering well is constructed, it is put into operation immediately to timely lower the groundwater level and keep running around the clock. The excavation of the foundation pit is carried out two weeks after pre-dewatering. When the foundation pit is excavated to the base, except for the reserved drainage outlets, the remaining pipe wells are pulled out and backfilled, and a cushion layer is constructed. First, the water is pumped out with a water pump, and then the pipe wells are backfilled with coarse sand to the bottom elevation of the cushion layer, and the well pipes are filled with concrete of the same grade as the cushion layer. At the same time: Establish a dynamic monitoring network for groundwater along the line, and use the standby wells outside the pit as observation wells to observe the daily monitoring data of the groundwater level, the monthly monitoring data of the groundwater quality, the daily drainage volume data of the foundation pit, and the drainage sand content data; Establish a settlement monitoring network. Before the implementation of the dewatering project, settlement monitoring points are arranged according to the preset pumping influence range and the buildings within the pumping influence range. Continuous settlement monitoring is carried out during pumping. If the cumulative settlement reaches the warning value, measures are taken. If it is found through settlement monitoring that the settlement of the building has reached a dangerous level, pumping is stopped. When it is confirmed that the building settlement is caused by dewatering, a recharging measure is taken, and recharging is carried out using the standby wells outside the pit in the settlement area. The distance between the recharge well and the dewatering well is greater than 5.0 meters. Subsequently, the drainage construction of the foundation pit is carried out. Drainage ditches are set around or in the middle of the excavated foundation pit, and a sump is set every 15 meters to allow the seepage water and construction wastewater in the foundation pit to flow into them, and then they are pumped into the surface sedimentation tank by a water pump and discharged into the municipal pipe network after sedimentation treatment. The drainage ditches and sumps are deepened while excavating, keeping the bottom of the ditch lower than the bottom of the foundation pit by greater than or equal to 0.5 meters, and the sump lower than the bottom of the ditch by greater than or equal to 0.5 meters. Brick drainage ditches with a size of 400 mm × 400 mm are set on the ground around the foundation pit, and sedimentation tanks with a size of 1000 mm × 500 mm × 500 mm are set every 20 meters. Keep the groundwater level in the pit during excavation, ensuring that the groundwater is more than 1 meter below the excavation surface. The dewatering time lasts until the topsoil covering is completed. The dewatering of the foundation pit is carried out 15 to 20 days before the earth excavation, and the trial dewatering work is done well. When excavating to the construction floor slab, temporary drainage holes are set on the floor slab, and the holes are sealed after the topsoil covering and the internal paving layer construction are completed. Dewatering outside the foundation pit is carried out 7 to 10 days before the foundation pit excavation, and the water level is lowered to 5 meters below the ground surface. One drainage hole is arranged every 200 square meters.

5. The construction method of an urban open-cut tunnel group in an ecologically sensitive area according to claim 1, characterized in that: In the third step, foundation pit excavation and support erection construction are carried out. During foundation pit excavation and support, earthwork excavation adopts the method of overall layered or stepped layered excavation, with the layered thickness less than or equal to 2 meters. During the excavation process, the temporary slope on the excavation surface is less than or equal to 1:1.

5. Excavation is carried out layer by layer, and the next layer is excavated after the support is completed; during the excavation process, the leakage positions on the retaining wall are blocked; for the soil within 30 cm above the designed bottom elevation of the foundation pit, the local excavated depressions are filled with sand, and sump pits are set up to pump out the accumulated water at the bottom of the pit.

6. The construction method of an urban open-cut tunnel group in an ecologically sensitive area according to claim 1, characterized in that: In Step 4, the construction of the reinforced concrete crown beam and the reinforced concrete support beam is carried out. The technological process is as follows: the earthwork under the support beam is leveled, compacted, the measurement and setting out are carried out, the bituminous felt isolation layer is laid, the steel bars are tied, the formwork is installed, the steel bars and formwork are inspected and accepted, the concrete is poured and cured. Before the construction of the retaining piles, the concrete guide wall is set up first. The outer guide wall is used as the retaining wall for earth excavation. After the construction of the retaining pile retaining structure is completed, the inner guide wall is demolished, and it is loaded and transported out together with the earthwork, and the concrete debris, earthwork and impurities within the range of the wall top are removed and washed clean with water. According to the design elevation, the positions of each reinforced concrete collar beam and support are set out by using a level and in accordance with the foundation pit retaining wall, and the base is cleaned to ensure the horizontality of the foundation pit bottom. The bottom formwork of the support adopts C20 concrete bottom formwork with a thickness of 15 cm and a width 15 cm wider than the width of the support beam. After the earthwork excavation and leveling are completed, the base is tamped, leveled with gravel, and the two sides are provided with fixed wooden formwork with a thickness of 4 cm. The concrete is poured, and the concrete is vibrated solid by a flat vibrator. After the surface is pressed twice with wooden wedges, it is troweled smooth with an iron plate. After the concrete bottom formwork is poured, it is covered with straw bags and watered for curing for 3 days. After the strength of the concrete bottom formwork reaches 50%, the steel bars are tied. A layer of isolation layer is set on the surface of the concrete bottom formwork. Before the steel bars are tied, steel pipe scaffolds are erected on both sides and one side of the support beam. After the steel bars are tied and formed, the steel pipe scaffolds are removed. The framework is placed on the bottom formwork. The crown beam, concrete support and concrete corner brace are erected with composite formwork. The support system is jointly stressed by connecting 50×80 wooden squares, 48×3.5 short steel pipes, M12 tie bolts and fasteners. The surface of the formwork is flat, the joints are tight, and there is no leakage of slurry. For those with uneven diameters and edges and local unevenness, they should be repaired and corrected in time, otherwise they cannot be used. The formwork is coated with release oil before formwork erection. The release oil adopts clear engine oil. The formwork support adopts steel pipes with a diameter of 48 mm and a length of 1.8 m, which are driven into the soil by more than or about 0.6 m, with a spacing of 80 cm and two longitudinal steel pipes connected. Before pouring, the position, elevation, cross-sectional dimensions of the formwork, the stability of the formwork and support, and the joint conditions are reviewed. The concrete adopts commercial concrete, and the commercial concrete is transported to the site by a drum-type transport vehicle with a capacity of 6 cubic meters or 8 cubic meters and is pumped to each pouring point by a truck pump or a stationary pump. The truck pump selects a concrete pump truck with a boom length of 21 m. The truck pump or the stationary pump is parked on the construction access road for pumping. The formwork of the crown beam, concrete support and concrete corner brace is removed when the concrete strength can ensure that the surface and edges and corners are not damaged due to formwork removal after the concrete has finally set. The concrete is cured by watering and moisturizing, and the surface is covered with burlap. The production water of the construction site water supply system is used, and the curing time is 7 days. After the concrete strength of the crown beam, concrete support and concrete corner brace reaches 95%, the lower layer of earthwork excavation is carried out; the method for demolishing the foundation pit concrete support is to break it by mechanical cutting. The support demolition sequence is as follows: first, the secondary support is demolished, and then the opposite strut is demolished. When demolishing the support beam, the connecting rod is demolished first and then the main support. When demolishing each support beam, it is cut from the middle. The protection of the wall panel is strengthened during the support demolition to prevent the support beam from damaging the roof slab of the tunnel main structure. The protective measure of laying wooden squares on the roof slab is adopted.

7. A construction method for an urban open-cut tunnel group in an ecological sensitive area according to claim 1, characterized in that: In the fifth step, the main structure construction is carried out. First, construction preparation work is carried out. After the foundation pit is excavated to the design elevation, the foundation pit inspection is carried out, and the structure is measured and lofted. Then, the plain cushion construction is carried out. The cushion concrete is C20 and 20 cm thick. The cushion construction is carried out after the excavation surface. The accumulated water in the foundation pit is drained, the loose soil in the foundation pit is removed, the top of the anti-pull pile is cleaned and leveled, and the silt and other sundries are removed. After the foundation pit is cleaned, the base is rammed with a rammer, and the bearing capacity of the foundation is measured. When the cushion concrete is paved, the surface elevation is controlled according to the pre-buried level pile. The concrete is vibrated with a flat vibrator. After the cushion concrete starts to set and before it finally sets, the surface layer is re-compacted, and sufficient curing is carried out to prevent looseness, sanding, and peeling. The pouring thickness of the cushion is controlled according to the pre-buried elevation control pile, and the surface is finished and cured to make the cushion surface free of honeycombs, pockmarks, and cracks. Then, the support is arranged. The support for the main structure frame concrete construction is a full hall disc buckle support. Each disc buckle vertical pole in the full hall disc buckle support can bear a vertical load of 8 to 9 tons. The vertical load includes the side pressure of the side wall concrete, the weight of the roof concrete, the weight of the formwork, the construction load, and the wind force acting on the formwork support. The longitudinal and transverse spacing of the disc buckle support is 60 cm and 90 cm, and the transverse spacing of the disc buckle support adjacent to the upper chamfer is 60 cm. No unloading device is set during construction. Then the formwork construction is carried out. The outer formwork of the concrete project uses the side wall of the enclosure structure. Before the construction of the side wall, the wall surface of the enclosure structure is first trimmed and leveled. The formwork consists of three parts: the bottom formwork, the side wall, and the top formwork. They are assembled on site. The construction formwork of the bottom plate and a section of the side wall uses a large steel formwork, which is processed into a frame with angle steel and channel steel. The bakelite board is connected to the frame as a whole and processed into blocks. It is assembled on site. The formwork uses 2440 mm × 1220 mm × 15 mm plywood as the panel, 60 mm × 80 mm square wood as the secondary rib, φ48* 3.5mm steel pipe is used as the main rib. The outer wall is poured 30cm above the armpit corner of the bottom plate when the bottom plate concrete is poured. Two rows of vertical pre-embedded screws are used in the outer wall. The upper row is the tension screw. The lower row of pre-embedded screws are welded to the main reinforcement of the structure and do not penetrate the entire bottom plate to prevent the movement of the formwork. The longitudinal spacing of the screws is 600mm and the vertical spacing is 500mm. The secondary ribs are made of 60mm*80mm square wood. The main rib steel pipe is arranged vertically, and a steel pipe is set at the top for tensioning. The side wall formwork system of the main structure of the open-cut section adopts single-sided formwork and uses three-dimensional steel. The angle trusses and embedded parts are used as the support system of the formwork to fix the formwork firmly. The formwork panel adopts a 4.5m×1.5m×5mm integral large steel formwork, the surrounding ribs are 75mm*8mm steel plates, the vertical secondary ribs are 75mm*50mm angle steels, and the horizontal connection is made of 70mm*6mm steel plates. The secondary back rib spacing is less than 300mm. The main back ribs on the vertical ribs are 10# double channel steel welded on the back ribs. The bracket adopts a double 14# channel steel tripod with a spacing of 750mm. The top plate formwork system of the main structure of the open-cut section adopts Steel pipe scaffolding, top support, secondary square wood and main steel pipe support, the template uses 2440 mm × 1220 mm × 15 mm plywood as the panel, 8*8 cm square wood @ 30 cm and double Φ48 steel pipe @ 30 cm two secondary forms, 10# I-beam @ 80 cm as the main scaffolding, and the disc-type bracket is used to set up the full-hall scaffolding support. According to the use of disc-type brackets 48 and 60, the horizontal spacing of the brackets is 90 cm, and the vertical spacing is 60 cm, 90 cm and 120 cm, and the erection step distance is 1.5 meters. The cut edges of the formwork are protected with edge-sealing paint, and the wooden formwork is processed on the construction site. Bottom battens are provided at the joints of the top plate formwork, and sponge strips are added to seal the joints of the vertical formwork. Cleaning ports are set at the top plate and the ends. Before pouring concrete, a dust collector is configured to clean the sundries inside the formwork. Thin sponge pads are embedded or putty is applied at the joints to eliminate the gaps. Before erecting the formwork, the formwork is polished, rust-removed, oiled, and trial-assembled. When erecting the formwork, the embedded parts are installed and fixed. The formwork release agent uses clean engine oil or formwork release agent. The exposed length of the adjustable screw rod does not exceed 2 / 3 of the total length of the screw rod. Before the formwork enters the site, the formwork and the usage parts are numbered, and the formwork is arranged to enter the site in batches in an orderly manner to meet the requirements of on-site construction and avoid occupying more space on the site. After the base waterproof coating is constructed to meet the requirements, the bottom slab steel bars are tied. The side wall and top plate steel bars are tied after the bottom slab concrete construction is completed and the inner formwork and bottom formwork are installed, and various joint bars are reserved according to the design. Subsequently, concrete pouring is carried out. First, the bottom slab concrete is poured. The concrete pouring adopts the inclined-layer method and reaches the top at one time. The thickness of each layer ranges from 30 cm to 40 cm. The concrete pump truck starts pouring from the four corners on both sides of the foundation pit, allowing the concrete to flow naturally to form an inclined plane. Then, the middle partition wall and the outer side wall concrete are poured. For the tunnel concrete structure, the middle partition wall is poured first, and then the outer side wall is poured. The inclined-layer construction method is adopted to control the one-time pouring height, and the concrete is laid and tamped in layers, and the cycle is advanced as a whole. The thickness of each layer is 30 cm. Two concrete pump trucks are used for simultaneous pouring, and the side walls and the middle wall on both sides of the frame are poured symmetrically at the same time. Then, the top plate concrete is poured. The concrete pouring adopts the inclined-layer method and reaches the top at one time. The thickness of each layer ranges from 30 cm to 40 cm. The concrete pump truck starts pouring from the four corners on both sides of the foundation pit, allowing the concrete to flow naturally to form an inclined plane. Then, concrete vibration is carried out. The concrete is vibrated with an inserted vibrator. The moving distance of the vibrator does not exceed 1 times the action radius of the vibrator.It is 5 times, and insert it into the lower-layer concrete. The insertion depth ranges from 5 cm to 10 cm. The concrete is tamped densely without missing vibration, under-vibration or over-vibration. The fast-insertion and slow-withdrawal method is adopted, and the vibration points are evenly arranged. Vibration should be strengthened at construction joints and embedded parts. During vibration, do not touch the formwork, steel bars, waterstop belts and the floor slab. After the top slab concrete is vibrated densely, before final setting, the surface original mortar is leveled, tamped and polished. If the moisture on the vibration surface is greater than the preset water volume, use a vacuum pump and connect a 15-square-meter vacuum suction pad to suck away the accumulated water on the concrete surface area, and then carry out the maintenance of the concrete. After the concrete pouring is completed and initial setting occurs, sprinkle water for maintenance to ensure that the concrete surface is in a wet state, and at the same time cover the geotextile on the concrete surface; conduct tunnel waterproof construction. First, determine the self-waterproofing of the concrete structure. The waterproof concrete is prepared by adjusting the mix ratio and adding admixtures and admixtures. Determine the anti-seepage grade of the structural concrete, the water-binder ratio of the structural concrete and the minimum dosage of the binder material according to the strength of the concrete structure and the depth of the structure embedding. The top slab concrete and the side wall concrete poured together with the top slab adopt the addition of an appropriate amount of high-quality fly ash and slag to reduce dry shrinkage and temperature difference shrinkage; then carry out the construction of waterproof coiled materials. The side wall adopts a 1.5-mm-thick pre-laid polymer waterproof coiled material, the floor slab adopts a 1.5-mm-thick pre-laid polymer coiled material, and the top slab adopts a flexible waterproof layer. The waterproof construction progress is consistent with the main structure construction progress. The waterproof coiled material of the floor slab is constructed for each construction flow section after the foundation pit excavation cushion layer is completed. The construction of the waterproof coiled material of the floor slab for each flow section is controlled to be completed within 2 working days. The pre-laid polymer waterproof coiled material of the side wall is constructed before the tunnel side wall construction. Each flow section is completed within 5 days. The single-component polyurethane waterproof coating of the top slab is completed within 2 working days after the top slab construction is completed and conditions are met. The 7-cm-thick C20 fine aggregate concrete protective layer is constructed after the waterproof coiled material construction is completed.

8. A construction method for an urban open-cut tunnel group in an ecologically sensitive area according to claim 1, characterized in that: In the sixth step, the earthwork backfilling is carried out. The earthwork is spread by a bulldozer, and the layer thickness is not more than 30 cm. The two sides of the tunnel frame are backfilled according to the backfilling construction of the bridge culvert back. It is rammed with a rammer with an impact force range of 1 to 3 tons. The topsoil of the roof is constructed according to the upper soil filling process of the bridge. The part within 50 cm from the roof is statically pressed by a roller, and the part more than 50 cm thick is filled with soil by a dump truck with a loading range of 10 to 15 tons. The bulldozer cooperates with the grader to spread and level it, and the roller vibrates and compacts it. The compactness is not less than 95%. After one layer is filled, continue to fill and carry out the next process construction. Subsequently, the anti-collision wall construction of the open section top side is carried out. When constructing the bottom plate, multiple iron parts are pre-buried in an orderly manner. The multiple iron parts are used to reinforce and support the U-shaped retaining wall concrete and the anti-collision wall. The anti-collision wall at the top of the open section retaining wall is constructed after the retaining wall concrete reaches the preset strength. The formwork erection and concrete pouring of the open section retaining wall and the anti-collision wall are the same as those of the tunnel main structure.

9. The construction method of an urban open-cut tunnel group in an ecologically sensitive area according to claim 1, characterized in that: In the sixth step, first, the electrical installation project is carried out, including tunnel power supply and distribution, tunnel power distribution, tunnel lighting, lightning protection and grounding, pump room and auxiliary building lighting, tunnel management center, computer network system, closed-circuit television monitoring system, traffic video monitoring, electromechanical equipment automatic control system, fire alarm and linkage control system, wired broadcast system, emergency telephone system, wireless communication system, and UPS uninterruptible power supply system. Then, the installation and commissioning of the tunnel fan and control box are carried out. Finally, the decoration project, fire protection, and landscape project are constructed.

10. A construction method for an open-cut tunnel group in a city in an ecologically sensitive area, characterized in that It includes the following steps: Step 1: Construction confirmation; Step 2: Enclosure construction; Step 3: Foundation pit excavation; Step 4: Support construction; Step 5: Main body construction; Step 6: Auxiliary project construction; In the above step 1, obtain the geographical location, surrounding environment, and traffic flow of the tunnel group, obtain the lengths, widths, and burial depths of multiple tunnels in the tunnel group, divide the multiple tunnels in the tunnel group into multiple construction sections, and determine the construction sequence of multiple open-cut tunnels and construction sections in the tunnel group; In the above step 2, first carry out the construction of bored cast-in-place piles and secant bored piles. For bored piles, all-use full casing and rotary drilling rigs. The bored cast-in-place piles and high-pressure jet grouting piles form a cut-off curtain. The adjacent single piles of the secant bored piles are mutually occluded to form a pile wall. Among them, for the bored cast-in-place piles, first construct a reinforced concrete guide wall above the pile top. The width of the guide wall is 3.5 meters, the thickness is 35 cm, and the material is C25 concrete. Subsequently, accurately measure the pile center position as the control point for the rig positioning. After the pile foundation is in place, first remove obstacles at a soil depth of 2.5 meters to 3 meters, then use a pile driver to sink the steel casing into the completely weathered rock layer, and detect whether the verticality reaches the preset verticality. If the preset verticality is not reached, correct the verticality deviation. If the preset verticality is reached, take soil downward until the designed bottom elevation of the hole is reached. Subsequently, fabricate the steel cage and hoist it using a crane. The designed elevation is determined by the elevation of the top of the casing. When the steel cage is lowered, it is gradually lowered by positive or reverse rotation to prevent collision. After it is lowered to the designed elevation, it is fixed. Subsequently, pour concrete. For the reinforced piles, underwater C35 concrete is used, and for the plain piles, super-retarding C35 concrete is used. The concrete pouring conduit is connected by a screw thread sleeve rubber seal ring, with an inner diameter of 25 cm. The conduit is lowered into the hole using a crane. The bottom of the conduit is 30 to 50 cm higher than the bottom of the hole to ensure the discharging space at the lower opening. The upper opening of the conduit is connected to a concrete funnel, and the upper opening of the conduit is sealed with a water-stop plug. The concrete flows into the funnel through a chute. After more than 2 cubic meters of concrete is stored in the funnel, pull out the bottom cover of the funnel and pour concrete into the conduit, and keep the concrete pouring continuously. During the pouring process, measure the actual height of the concrete surface and calculate the buried depth of the conduit so that the bottom end of the conduit is buried more than 2 meters to 6 meters below the concrete surface. After the concrete pouring is completed, gradually remove the casing and the conduit. When the casing is lifted, pull up the casing and shake it to make the concrete flow into the space occupied by the casing. The buried depth of the casing is controlled at about 2 meters. The concrete is poured to 0.5 meters above the pile top elevation, and this part of the concrete is chiseled off before constructing the capping beam. After the pouring is completed, pull out the casing and the conduit. The setting time of the plain pile concrete is determined according to the single-pile forming time. The setting time of the plain pile concrete can be determined according to the following method. First, measure the time t required for a single pile to be formed, and then calculate it according to the following formula: T = 3t + K, where: T = the setting time of the plain pile concrete, K = the reserve time, generally taking 1.5t, t = the single-pile forming time of pile A and the single-pile forming time of pile B; In the above step 3, foundation pit excavation and support erection construction are carried out. During foundation pit excavation and support, the earthwork excavation adopts the method of overall layered or stepped layered excavation, with the layered thickness less than or equal to 2 meters. During the excavation process, the temporary slope on the excavation surface is less than or equal to 1:1.

5. The excavation is carried out in layers, and the next layer is excavated after the support is completed. During the excavation process, the leakage positions on the retaining wall are blocked. For the earthwork within 30 cm above the designed bottom elevation of the foundation pit, the local excavated depressions are filled with sand, and sump pits are set up to pump out the accumulated water at the bottom of the foundation pit. In the above step 4, the construction of the reinforced concrete capping beam and the reinforced concrete support beam is carried out. In the above step 5, the construction of the main structure of the tunnel is carried out. In the above step 6, the earthwork backfilling is carried out.

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