A large slope passage open cut construction method

Abstract

The application discloses a large-gradient passage underground excavation construction method, which comprises the following steps: reinforcing the existing building and surrounding rock mass; and carrying out passage construction; wherein the passage construction comprises forward construction from the slope top to the slope foot and reverse construction from the slope foot to the slope top, two linings are respectively constructed at the slope top and the slope foot during the forward construction, and a strong support structure is formed. Two linings are respectively constructed at the slope top and the slope foot, so that the strong support effect of the two linings is fully exerted, the deformation of the support structure is controlled, the disturbance to the surrounding rock mass and the building is reduced, and the construction process is safe and controllable. The forward construction and the reverse construction are mutually matched, the single excavation section is small, small-section excavation is realized, the gradient during one-way construction is greatly reduced, the mechanical equipment is provided with a construction access, the construction cost is reduced, the construction speed is improved, and the construction period is shortened.

Description

Technical Field

[0001] This invention belongs to the technical field of construction methods, specifically relating to a method for tunnel excavation with steep gradients. Background Technology

[0002] Soft geological conditions, also known as soft foundation systems, refer to foundations primarily composed of silt, silty soil, fill, miscellaneous fill, or other highly compressible soil layers. Soft foundation systems cannot meet the requirements for building foundations, necessitating measures to treat them.

[0003] During the construction of urban subways and rail transit facilities, due to terrain constraints, some access passages need to be connected to the station via the cut-and-cover method. Some access passages are characterized by poor geological conditions (located in soft foundation systems), large clearance heights, steep slopes, and parallel to existing buildings with small clearances. Constructing these passages using the existing cut-and-cover method presents significant construction difficulties and high safety risks. Summary of the Invention

[0004] The purpose of this invention is to provide a method for constructing tunnels with steep gradients by cutting and excavating, in order to solve the aforementioned problems existing in the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for constructing a tunnel with a steep gradient using the cut-and-cover technique includes the following steps:

[0007] Reinforcement of existing buildings and surrounding soil and rock masses;

[0008] Access road construction;

[0009] The construction of the passage includes forward construction from the top of the slope to the bottom of the slope and reverse construction from the bottom of the slope to the top of the slope. During forward construction, secondary linings are constructed at the top and bottom of the slope to form a strong support structure.

[0010] In one possible design, the tunnel construction includes the following steps:

[0011] For the construction of the straight section at the top of the tunnel slope, the initial support and secondary lining are constructed sequentially.

[0012] The upper rock mass of the inclined tunnel slope section is excavated in a forward segmented manner until the toe of the slope;

[0013] For the construction of the straight section at the toe of the passageway, the initial support and secondary lining are constructed sequentially.

[0014] The remaining rock mass of the slope section of the reverse segmented excavation channel extends to the top of the slope;

[0015] The double lining is closed;

[0016] The passage consists of a straight section at the top of the slope, a sloping section, and a straight section at the bottom of the slope, which are connected in sequence.

[0017] In one possible design, the upper rock mass of the channel slope section excavation in a forward segmented manner includes the following steps:

[0018] Excavate the upper rock mass of the slope section and construct the initial support at the arch crown;

[0019] Temporary support construction;

[0020] Construction of circumferential water-stop curtain.

[0021] In one possible design, the above steps are repeated until the tunnel slope is excavated;

[0022] The remaining rock mass of the reverse segmented excavation channel slope section includes the following steps:

[0023] Excavate the remaining rock mass on the slope section and construct the initial support outside the arch;

[0024] Construction of water-stop curtain;

[0025] Remove temporary supports;

[0026] Secondary lining construction;

[0027] Repeat the above steps until the tunnel slope is excavated.

[0028] In one possible design, the tunnel is constructed using the step method, with the upper step being excavated in a ring shape and a core soil reserved. The tunnel face is temporarily sealed with shotcrete, and a temporary inverted arch is set below the core soil.

[0029] The distance between the end of the secondary lining of the straight section at the top of the slope and the top of the slope is 1.5-2.5m; the distance between the end of the secondary lining of the straight section at the bottom of the slope and the top of the slope is 1.5-2.5m; a step is provided between the bottom of the slope and the slope, with a step height of 1.5-2.5m;

[0030] Temporary support includes temporary horizontal bracing and temporary inverted arches, with the temporary inverted arches located below the core soil.

[0031] In one possible design, during forward construction, the slope section is excavated in two sections, and the upper step section has a height greater than the minimum clearance and maximum slope requirements for mechanical construction. The ring excavation method with reserved core soil is adopted, and the reserved area shall not be less than 50% of the excavation section area. During reverse construction, when the excavation height in some locations is greater than 2m, it is necessary to excavate in steps again and set up temporary invert arches.

[0032] In one possible design, the construction of the water-stop curtain includes the construction of the waterproof membrane and the construction joint waterproofing.

[0033] The waterproofing membrane construction includes the following steps: measuring the clearance and trimming the base surface, cutting off protruding steel bar ends and grouting pipes on the base surface; using nail guns to lay hot-melt pads in a quincunx pattern on the base surface; and pressing the waterproofing membrane together.

[0034] The construction method for the construction joint includes the following steps: the waterstop is fixedly connected to the initial support by positioning steel bars; the waterstop is grouped into sets of 1m, and adjacent waterstops are heat-fused together; a waterproof reinforcement layer is provided outside the waterstop; adjacent waterproof reinforcement layers are connected by double-seam heat fusion.

[0035] In one possible design, the secondary lining construction includes the following steps: reinforcement installation; arch frame formwork construction; concrete pouring; grouting with formwork in place; and formwork removal.

[0036] In one possible design, reinforcement of the adjacent existing building includes grouting reinforcement and internal bracing reinforcement;

[0037] The reinforcement of the surrounding rock and soil includes advanced curtain grouting and advanced small guide pipes.

[0038] One possible design also includes monitoring and measurement, which includes several monitoring points, namely settlement monitoring points, clearance convergence monitoring points, and groundwater level monitoring points.

[0039] Beneficial effects:

[0040] The aforementioned reinforcement construction improved the geological conditions at the tunnel construction site, protecting existing buildings and structures while increasing the structural strength of the surrounding soil and rock, enhancing construction safety, meeting the tunnel's foundation requirements, and creating prerequisites for rapid and high-quality construction.

[0041] Secondary linings are constructed at the top and bottom of the slope to fully utilize their strong supporting effect, control the deformation of the support structure, reduce disturbance to the surrounding rock mass and buildings, and ensure safe and controllable construction process.

[0042] The coordinated use of forward and reverse construction, along with the small excavation cross-section in each operation, significantly reduces the slope during unidirectional construction, facilitating the entry of machinery and equipment. This not only lowers construction costs but also increases construction speed and shortens the construction period.

[0043] The secondary lining of the slope section is completed through reverse construction. The component of gravity along the slope surface ensures close contact between adjacent slabs, resulting in better construction quality. Furthermore, the close contact between adjacent slabs eliminates the risk of slippage in the secondary lining, eliminating the need for anti-slip piles inserted into the rock mass and facilitating the installation of a fully enclosed waterproof layer, leading to better waterproofing. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of a construction method for tunnel excavation with a large gradient.

[0045] Figure 2-11 The diagrams are, in order, structural schematics of each step in a method for constructing a tunnel with a steep gradient using the cut-and-cover technique.

[0046] In the picture:

[0047] 101. Straight section at the top of the slope; 102. Sloping section; 103. Straight section at the toe of the slope; 201. Initial support; 202. Secondary lining; 301. Core soil; 302. Temporary inverted arch; 303. Temporary horizontal bracing; Detailed Implementation

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the present invention will be briefly introduced below in conjunction with the accompanying drawings and descriptions of the embodiments or the prior art. Obviously, the following description of the structure of the accompanying drawings is only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. It should be noted that the description of these embodiments is for the purpose of helping to understand the present invention, but does not constitute a limitation of the present invention.

[0049] Example 1:

[0050] like Figures 1-11 As shown, a method for constructing a tunnel with a steep gradient using the cut-and-cover technique includes the following steps:

[0051] S100: Reinforcement of existing buildings and surrounding soil and rock masses.

[0052] Based on this, strengthening the foundation improves its structural strength, reduces the impact of construction on existing buildings and structures, minimizes disturbance to existing buildings and structures and surrounding soil and rock, and ensures construction progress while improving construction safety. Specifically, step S100, strengthening the foundation adjacent to existing buildings and structures and surrounding soil and rock, includes:

[0053] S110: Reinforcement of buildings adjacent to existing structures;

[0054] S120: Reinforcement of surrounding soil and rock mass.

[0055] Step S110, the reinforcement of existing structures, includes grouting reinforcement and internal support reinforcement. Based on the above design, grouting reinforcement involves uniformly injecting grout into the stratum through grouting pipes to form a new, strong, waterproof, and chemically stable matrix, filling the gaps between the tunnel segments and the stratum. Internal support reinforcement involves erecting a support structure inside the tunnel to improve its structural strength. These two methods, one internal and one external, work together to protect existing buildings and structures.

[0056] Step S120, the reinforcement of the surrounding soil and rock mass, includes advanced curtain grouting and advanced small-diameter guide pipes. Based on the above design scheme, advanced support is formed outside the construction area of ​​the passage to improve the structural strength of the surrounding soil and rock mass, reduce the deformation of the surrounding rock caused by excavation disturbance, and avoid accidents such as collapse, thus playing a protective role.

[0057] The reinforcement construction improved the geological conditions at the construction site, protecting existing structures and increasing the structural strength of the surrounding soil and rock, thus enhancing construction safety and meeting the foundation requirements of the passage. This created the prerequisites for rapid and high-quality construction. Based on this, it solved the problems of poor geological conditions and small clearances between existing structures in the prior art.

[0058] Taking subway tunnel construction as an example, the reinforcement of adjacent existing buildings and surrounding soil and rock in step S100 will be further explained:

[0059] Grouting reinforcement includes the following steps: estimating the parallel influence zone of the underground excavation; extending 5 rings of pipe segments outside the parallel influence zone of the underground excavation, and selecting 5 symmetrical points from bottom to top; filling each symmetrical point with cement grout.

[0060] The technical requirements for cement grouting are as follows: grouting pressure ≤ 0.03MPa; when grouting the lower points, the ball valve at the upper point is opened and used as an air vent; after grout emerges from the air vent, the ball valve is closed and pressure is maintained for 5 minutes; if leakage occurs during grouting, a double grout is used to apply a water-stop ring.

[0061] Optionally, the internal support reinforcement includes vertical steel supports located in the chord direction of each ring segment. The lower end of the vertical steel support is provided with a longitudinal concrete temporary support bottom beam, and the upper end of the vertical steel support is connected to the segment through steel wedges. The longitudinal concrete temporary support bottom beam is connected to the segment with rebar.

[0062] The advanced curtain grouting adopts a backward segmented grouting method that combines long and short grouting pipes. The grouting pipes are located 3m outside the outer contour line of the initial support 201. The grouting pipe holes correspond one-to-one with the grouting pipes. The grouting holes are evenly distributed and spaced 0.7m apart. Ordinary Portland cement with a pressure of 42.5MPa is used for grouting from bottom to top, and the grouting pressure is between 0.4-1MPa.

[0063] The advanced small guide pipe is located at the top of the arch. The front end of the small guide pipe is conical, and the tail end of the small guide pipe is welded with a steel reinforcement hoop. Every 150mm on the pipe wall is drilled with a quincunx pattern of drill holes with a diameter of 10mm. The tail end of the small guide pipe is provided with a grout-stopping section with no drill holes for no less than 30cm. The grout-stopping section is exposed and welded to the initial support 201. The initial grouting pressure is 0.5-1.0MPa, and the termination pressure is 1.5-2.0MPa.

[0064] The grouting control standards for both advanced curtain grouting and advanced small guide pipe grouting are as follows: after the grouting pressure reaches the final pressure, the pressure is maintained for 10 minutes, and the grouting volume is not less than 80% of the designed grouting volume. The grout diffusion radius is sufficient to allow the grout from adjacent grouting holes to form a loop.

[0065] S200: Channel construction, which includes forward construction from the top of the slope to the bottom and reverse construction from the bottom of the slope to the top. During forward construction, secondary lining 202 is constructed at both the top and bottom of the slope to form a strong support structure. Based on the above design scheme, forward construction initially forms the channel. On the basis of the initial support 201, temporary supports, and other protective structures, secondary lining 202 is constructed at both the top and bottom of the slope to fully utilize the strong support effect of secondary lining 202, control the deformation of the support structure, reduce disturbance to the surrounding rock mass and buildings, and ensure the safety and controllability of the construction process.

[0066] Simultaneously, the coordinated forward and reverse construction methods, along with the small excavation cross-section in each operation, significantly reduced the slope during unidirectional construction, facilitating the entry of machinery and equipment. This not only lowered construction costs but also increased construction speed and shortened the construction period. Furthermore, the shorter time the surrounding soil and rock mass was under weak support reduced safety risks.

[0067] Based on this, the problems of large clearance height and large slope in the existing technology are effectively solved.

[0068] Specifically, the construction of the S200 channel includes the following steps:

[0069] S210: Construction of the straight section 101 at the top of the passage slope, followed by the sequential construction of the initial support 201 and the secondary lining 202;

[0070] S220: The upper rock mass of the 102 section of the channel slope is excavated in a forward segment until the toe of the slope;

[0071] S230: Construction of the straight section 103 at the toe of the passage, with the initial support 201 and the secondary lining 202 constructed in sequence;

[0072] S240: Reverse segmented excavation of the remaining rock mass of the 102-section ramp to the top of the slope;

[0073] S250: Secondary lining 202 closed;

[0074] The passage includes a straight section 101 at the top of the slope, a sloping section 102, and a straight section 103 at the bottom of the slope, which are connected in sequence.

[0075] Based on the above design scheme, during the forward construction to the slope toe, the construction will be carried out in sections, with support erected as excavation progresses. Temporary inverted arches 302 will be constructed in a timely manner and closed into a ring. The temporary inverted arches 302 will be covered with soil and compacted to ensure sufficient thickness for mechanical equipment passage. During the reverse construction to the slope top, the principle of supporting before dismantling will be followed to improve safety. Where the excavation height exceeds 2m in some locations, the excavation will be carried out in steps again, and temporary inverted arches 302 will be set up.

[0076] Step S220, the forward segmented excavation of the upper rock mass of the channel slope section 102, includes the following steps:

[0077] S221: Excavate the upper rock mass of slope section 102 and construct the initial support 201 at the arch crown;

[0078] S222: Temporary support construction;

[0079] S223: Construction of circumferential water-stop curtain;

[0080] S224: Repeat the above steps until the tunnel slope is excavated.

[0081] Based on the above design scheme, the tunnel is supported by the initial support 201 and temporary supports, placing it under the support of a weak support structure. Excavation continues to the toe of the slope, where the secondary lining 202 is constructed. This allows the secondary lining 202 at the top of the slope and the secondary lining 202 at the toe to form a strong support structure, effectively improving the structural strength of the tunnel and shortening the time the tunnel is under weak support. A circumferential water-stop curtain provides complete waterproofing and seals any leaks at the initial support 201, ensuring its strength and rigidity.

[0082] Step S240, reverse segmented excavation of the remaining rock mass of the channel slope section 102, includes the following steps:

[0083] S241: Excavate the remaining rock mass of the slope section 102 and construct the initial support 201 outside the arch;

[0084] S242: Construction of water-stop curtain;

[0085] S243: Remove temporary supports;

[0086] S244: Secondary lining 202 construction;

[0087] S245: Repeat the above steps until the tunnel slope is excavated.

[0088] Based on the above design scheme, during forward construction, in order to improve the construction speed, only the initial support 201 is constructed at the top of the slope section 102, and the lower part of the ramp is supported by a temporary inverted arch 302. The overall structural support performance is poor and can only be used as a temporary support. Therefore, during reverse construction, it is necessary not only to excavate the remaining rock mass, but also to supplement the initial support 201 and water-stop curtain structures on the sides and bottom of the slope section 102, and then construct the secondary lining 202 on this basis to ensure that the structural strength of the passage meets the design requirements.

[0089] Optionally, the tunnel can be constructed using a stepped method. The upper step is excavated in a ring shape, with a core soil layer 301 reserved. The tunnel face is temporarily sealed with shotcrete, and a temporary invert arch 302 is installed below the core soil layer 301. Based on this, the reserved core soil layer 301 and the temporary invert arch 302 provide a structurally strong working position for machinery, facilitating faster construction. Simultaneously, since the tunnel excavation affects the structural strength of the surrounding soil and rock, the temporary invert arch 302 is installed promptly as excavation progresses, preventing excessive disturbance.

[0090] Optionally, the distance between the end of the straight section 101 of the secondary lining 202 at the top of the slope and the top of the slope is 1.5-2.5m; the distance between the end of the straight section 103 of the secondary lining 202 at the toe of the slope and the toe of the slope is 1.5-2.5m; a step with a height of 1.5-2.5m is provided between the toe of the slope and the slope. Based on this, a construction joint is reserved to facilitate the subsequent construction and closure of the secondary lining 202.

[0091] Optionally, the temporary support includes a temporary cross brace 303 and a temporary invert arch 302, with the temporary invert arch 302 located below the core soil 301. It is readily understood that the temporary cross brace 303 and the temporary invert arch 302 can be constructed as any suitable structure, and the present invention does not impose any limitations on this.

[0092] The excavation requirements for slope section 102 are as follows: When constructing in the forward direction, slope section 102 shall be excavated in two sections, and the upper step section shall be higher than the minimum clear height and maximum slope requirements for mechanical construction; the 301 method of reserving core soil for ring excavation shall be adopted, and the reserved area shall not be less than 50% of the excavation section area; when constructing in the reverse direction, if the excavation height in some locations is greater than 2m, it is necessary to excavate in steps again and set up temporary invert arches 302.

[0093] For the initial support 201, the initial support 201 includes a steel arch frame, precast concrete blocks, and anchor pipes. The outer side of the steel arch frame is sprayed with an annular concrete sealing surface. The steel arch frame is erected vertically from bottom to top in units. The precast concrete blocks are wedged between the outer edge of the steel arch frame and the annular concrete sealing surface. The anchor pipes connect the arch feet of the steel arch frame to the arch wall.

[0094] Based on this, the working face was sealed with shotcrete before the construction of the initial support 201, with a concrete thickness of 5cm. A ring-shaped concrete sealing surface was constructed to refine the shape of the passage. Grouting was preferred inside the anchor pipes to increase their strength. Concrete pads were also provided at the arch feet of the steel arch frame to reduce settlement.

[0095] Preferably, an isolation plate is installed above the connecting steel plate at the arch foot of the steel arch frame to make the sprayed concrete at the arch foot position more regular and to prevent concrete from flowing into the connecting bolt holes, thereby reducing the amount of chiseling work when repairing the concrete and ensuring the quality of subsequent connections.

[0096] Furthermore, several steel arch frames are provided and spaced apart along the longitudinal direction. Each steel frame is connected by φ22 steel bars, with a circumferential spacing of 1m on both sides. A double-layer steel mesh is provided between adjacent steel arch frames, and a concrete layer is provided between the double-layer steel mesh.

[0097] The concrete layer construction includes the following steps: laying one layer of reinforcing mesh; injecting concrete until it solidifies; and laying another layer of reinforcing mesh. When injecting concrete, it is applied vertically in layers and sections from bottom to top, with a spraying distance not exceeding 1 meter; the concrete layer at the arch is 6 cm thick, and the concrete layer on the side walls is 8 cm thick; the next layer is sprayed after the previous layer has solidified; coarse aggregate is mixed in to reduce rebound and ensure the quality of the concrete layer.

[0098] In steps 223 and 242, the construction of the water-stop curtain includes the construction of a waterproof membrane and the waterproofing of construction joints. The waterproof membrane is used to seal leaks at the initial support 201 and achieves complete waterproofing. The waterproofing of construction joints is used to seal the gaps between adjacent secondary linings 202 to reduce leakage.

[0099] The waterproofing membrane construction includes the following steps: measuring the clearance and trimming the base surface, cutting off the protruding steel bar ends and grouting pipes on the base surface; using nail guns to lay hot-melt pads in a quincunx pattern on the base surface; and pressing the waterproofing membrane together.

[0100] The hot-melt pads are spaced 50×50cm at the arch and 70×70cm at the sidewalls. The waterproofing membrane at the arch is laid with appropriate looseness to allow for deformation during the pouring of the secondary lining 202 concrete, preventing it from becoming too tight and causing gaps. The long side of the waterproofing membrane is no less than 10cm, and the short side no less than 15cm. The waterproofing membrane joints are double-sealed, with a distance greater than 1.5m from the construction joints. The waterproofing membrane extends at least 1.5m beyond the horizontal joints of the sidewalls and the circumferential construction joints at both ends of the secondary lining 202, to facilitate subsequent overlapping construction.

[0101] The construction method for the construction joint includes the following steps: the waterstop is fixedly connected to the initial support 201 by positioning steel bars; the waterstop is a group of 1m, and adjacent waterstops are heat-fused together; a waterproof reinforcement layer is provided outside the waterstop; adjacent waterproof reinforcement layers are connected by double-seam heat fusion.

[0102] Among them, the waterstop is a centrally embedded steel-edged rubber waterstop, and the waterstops at the arch and invert arch positions are installed in a basin-type manner, while the waterstops at other positions are installed horizontally; the outer side of the waterstop is tightly attached to the hot melt pad block through a waterproof reinforcement layer.

[0103] The method for constructing a steep-slope tunnel using the cut-and-cover method also includes the following steps:

[0104] S300: Monitoring and Measurement.

[0105] Therefore, we need to monitor the construction progress in real time to ensure the safety of the construction.

[0106] The monitoring and measurement system includes several monitoring points: one settlement monitoring point is set every 20m along the tunnel direction on the ground; one settlement monitoring point is set every 10m at the arch crown; and one clearance convergence monitoring point is set every 10m at the arch waist and sidewalls. A set of groundwater level monitoring points is set every 40m along the tunnel direction within a 5m radius on both sides of the tunnel, at a depth 3m below the tunnel's designed floor slab. The monitoring and measurement frequency is twice per day.

[0107] The monitoring benchmarks are as follows: cumulative value of arch subsidence and surrounding surface subsidence: 30mm; rate: 3mm / d; cumulative value of net clearance convergence: 30mm; rate: 2mm / d; cumulative value of groundwater level: 1m; rate: 0.5m / d.

[0108] Example 2:

[0109] This embodiment, based on Embodiment 1, provides the construction method for the secondary lining 202 in Embodiment 1, as follows:

[0110] The construction of the secondary lining 202 includes the following steps:

[0111] Reinforcing steel installation;

[0112] Based on this, the rebar joints are single-sided welded and the ends are pre-bent to ensure coaxiality; on-site installation is used to prevent damage to the waterproof membrane; the inner layer of the rebar has circumferential main bars with rebar supports and the outer layer has concrete spacers. The rebar supports are used to isolate the rebars from the waterproof membrane, and the concrete spacers are ≥4 per m2.

[0113] Arch frame formwork construction;

[0114] Based on this, long strip-shaped wooden formwork is used. The inner side of the wooden formwork is connected to the reinforcing bars through fastener-type supports, and the outer side of the wooden formwork is equipped with double-section steel pipe circumferential main beams. The wooden formwork, fastener-type supports, and double-section steel pipe circumferential main beams form an arch frame formwork.

[0115] The bottom of the arch frame formwork is equipped with a wooden pad, and the top and sides of the arch frame formwork are equipped with adjustable supports. Pouring holes and tamping windows are pre-reserved on both sides of the arch waist and the arch top of the arch frame formwork, and a waste blowing hole is pre-reserved at the bottom. Wooden end formwork is provided on the arch frame formwork, and the end formwork is equipped with waterstops and wooden wedges. The waterstops are used for waterproofing, and the wooden wedges connect to the steel pipes to form a diagonal bracing structure.

[0116] Concrete pouring;

[0117] Based on this, before pouring, grouting pipes and venting pipes are pre-embedded at the arch top position, and debris and garbage in the arch frame template are cleaned through the garbage blowing hole; during pouring, pouring is carried out symmetrically in windows from bottom to top, and a discharge pipe is provided at the arch top, with a 3-5m flexible hose of the same diameter added to the front end of the discharge pipe so that the pipe opening faces downward.

[0118] After pouring, the height difference between the two sides of the concrete should not exceed 50cm, and the free fall height should not exceed 2m. If the height difference exceeds this, it should be addressed by extending the flexible hose. Simply put, when the concrete is poured thickly, it should be tamped in real time through the tamping window; as the concrete gradually rises, the tamping window should be closed promptly to prevent leakage. During the capping process, concrete should be poured from the inside towards the end formwork to expel air. The secondary lining of the closed slab (202) uses micro-expansion concrete to ensure a tight seal.

[0119] Grouting with mold;

[0120] Therefore, after the concrete is poured, cement grout is used for grouting the arch with the formwork in place, at a grouting pressure of 0.8 MPa. When cement grout emerges from the vent pipe, it is sealed, and the pressure is maintained for 30 minutes. Grouting is then stopped, and the grouting port valve is closed. The condition of the formwork and supports should be monitored in real time during the grouting process; grouting should be stopped immediately if any abnormalities are detected.

[0121] Demolding.

[0122] Based on this, the secondary lining 202 of slope section 102 is constructed in reverse, allowing adjacent secondary linings 202 to adhere tightly under gravity. This results in high construction quality, eliminates the risk of slippage, and eliminates the need for anti-slip piles inserted into the rock mass. Furthermore, it facilitates the installation of a fully enclosed circumferential waterproof layer, improving the overall effectiveness of the method.

[0123] And it is easy to understand that the construction method of the secondary lining 202 in this embodiment can be used for the construction of all secondary linings 202 in Embodiment 1, including but not limited to the second section of the straight section 101 at the top of the slope, the secondary lining 202 of the straight section 103 at the bottom of the slope, and the secondary lining 202 of the sloping section 102.

[0124] Example 3:

[0125] Benefit analysis:

[0126] For example, see Tables 1 and 2 for details of the Shenzhen Metro project (slope section length 25.8m, cross-sectional area 65.8㎡, perimeter 31.5m).

[0127] 1. Cost Comparison

[0128] Table 1 Analysis of Differences in Engineering Quantities for Single Channels

[0129]

[0130] Construction cost calculation

[0131] (1) Excavation

[0132] CRD method manual excavation: 1697.64 × 148.36 = 251861.87 yuan;

[0133] Two-stage bench excavation: 1697.64 × 70.14 = 119072.47 yuan.

[0134] (2) Temporary steel frame

[0135] CRD method temporary steel frame (including materials, fabrication, installation and dismantling): 20.31×(6283.15+822.83+289.58)=150203.82 yuan;

[0136] Two-stage stepped temporary steel frame (same as above): 6.82 × (6283.15 + 822.83 + 289.58) = 50437.72 yuan.

[0137] (3) Temporary support shotcrete

[0138] Material: 210.27×350=73594.5 yuan;

[0139] Support cost: 841.08 × (50.7 + 5.82 × 2) = 52432.93 yuan;

[0140] Demolition cost: 210.27 × 31.14 = 6457.81 yuan.

[0141] In summary, the cost savings per channel are: (251861.87-119072.47)+(150203.82-50437.72)+(73594.5+52432.93+6457.81)=365040.74 yuan.

[0142] 2. Comparison of construction periods

[0143] According to on-site construction statistics, the CRD method involves four manual excavations, which can complete one cycle per day. With step ① as the critical path, each cycle advances one scaffold and 0.5m. The two-stage bench mechanical excavation can complete five cycles every three days. With the upper bench as the critical path, each cycle advances two scaffolds and 1m.

[0144] Table 2. Analysis of Construction Period Differences

[0145]

[0146] From the perspective of the entire project, the two channels saved a total of 730,081.48 yuan, shortened the construction period by 31 days, and achieved good quality in secondary lining construction, resulting in significant social and economic benefits.

[0147] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for constructing a tunnel with a steep gradient using the cut-and-cover technique, characterized in that, Includes the following steps: Reinforcement of existing buildings and surrounding soil and rock masses; Access road construction; The construction of the passage includes forward construction from the top of the slope to the bottom of the slope and reverse construction from the bottom of the slope to the top of the slope. During forward construction, secondary lining (202) is constructed at the top and bottom of the slope respectively to form a strong support structure. The construction of the passageway includes the following steps: Construction of the straight section (101) at the top of the channel slope: the initial support (201) and the secondary lining (202) are constructed in sequence. The upper rock mass of the inclined tunnel slope section (102) is excavated in a forward segmented manner until the toe of the slope; Construction of the straight section (103) at the toe of the passage: the initial support (201) and the secondary lining (202) are constructed in sequence. The remaining rock mass of the reverse segmented excavation channel slope section (102) extends to the top of the slope; The secondary lining (202) is closed; The passage includes a straight section at the top of the slope (101), a sloping section (102), and a straight section at the bottom of the slope (103) that are connected in sequence. The upper rock mass of the inclined section (102) of the channel excavation in the forward segment includes the following steps: Excavate the upper rock mass of the slope section (102) and construct the initial support (201) at the arch. Temporary support construction; Construction of circumferential water-stop curtain; Repeat the above steps until the tunnel slope is reached; The remaining rock mass of the reverse segmented excavation channel slope section (102) includes the following steps: Excavate the remaining rock mass of the slope section (102) and construct the initial support (201) on the part outside the arch. Construction of water-stop curtain; Remove temporary supports; Secondary lining (202) construction; Repeat the above steps until the tunnel slope is excavated; The tunnel is constructed using the step method. The upper step is excavated in a ring and a core soil (301) is reserved. The tunnel face is temporarily sealed with shotcrete, and a temporary inverted arch (302) is set below the core soil (301). The distance between the end of the secondary lining (202) of the straight section (101) at the top of the slope and the top of the slope is 1.5-2.5m; the distance between the end of the secondary lining (202) of the straight section (103) at the bottom of the slope and the bottom of the slope is 1.5-2.5m; a step is provided between the bottom of the slope and the slope, with a step height of 1.5-2.5m; The temporary support includes temporary cross bracing (303) and temporary invert arch (302), with the temporary invert arch (302) located below the core soil (301); During forward construction, the slope section (102) is excavated in two sections, and the upper step section is higher than the minimum clear height and maximum slope requirements for mechanical construction. The ring excavation method with reserved core soil (301) is adopted for excavation, and the reserved area shall not be less than 50% of the excavation section area. During reverse construction, when the excavation height in some locations is greater than 2m, it is necessary to excavate in steps again and set up temporary inverted arches (302).

2. The construction method according to claim 1, characterized in that, Water-stop curtain construction includes waterproofing membrane construction and construction joint waterproofing construction; The waterproofing membrane installation includes the following steps: Measure the clearance and trim the base surface, cut off the protruding steel bar ends and grouting pipes on the base surface; use nail guns to lay hot melt pads in a quincunx pattern on the base surface; Waterproof membrane pressing; The construction method of the construction joint includes the following steps: the waterstop is fixedly connected to the initial support (201) by the positioning steel bar; the waterstop is a group of 1m, and the adjacent waterstops are heat-fused together; a waterproof reinforcement layer is provided outside the waterstop; the adjacent waterproof reinforcement layers are connected by double-seam heat fusion.

3. The construction method according to claim 1 or 2, characterized in that, The construction of the secondary lining (202) includes the following steps: Reinforcing bar installation; arch frame formwork construction; concrete pouring; grouting with formwork in place; formwork removal.

4. The construction method according to claim 1, characterized in that, Reinforcement of existing buildings includes grouting reinforcement and internal bracing reinforcement; The reinforcement of the surrounding rock and soil includes advanced curtain grouting and advanced small guide pipes.

5. The construction method according to claim 1, characterized in that, It also includes monitoring and measurement, which includes several monitoring points, namely settlement monitoring points, airspace convergence monitoring points and groundwater level monitoring points.

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