Intersection protection construction method for intersecting shield

Abstract

The invention provides an intersecting shield interval protection construction method, which belongs to the technical field of building construction, and comprises the following steps: firstly, excavating an open cut foundation pit at an intersection, arranging a cast-in-situ bored pile and a crown beam as an enclosure structure in the foundation pit, and arranging a steel support system at the same time. And after the enclosure structure is completed, the foundation pit is excavated to the designed depth, and reinforced concrete supporting piles and pile top beams are constructed. And on the basis, a reinforced concrete protection plate is poured to form a sheet pile structure type protection structure system. And finally, foundation pit filling is completed in a backfilling mode. Before the shield passes through the cross point, a test section is arranged to collect related construction data, and preparation is made for subsequent formal tunneling. And in the actual shield tunneling process, the tunneling speed and the soil bin pressure are controlled, and synchronous grouting is conducted. And after crossing the cross point, arranging closed rings in the front and back areas, and carrying out wall back grouting by adopting double-liquid slurry. And finally, a geological radar is used for detecting the cavity and repairing, and the problem of mutual influence in up-down close-distance crossed tunnel construction is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of building construction, and in particular relates to a construction method for protecting an intersecting shield section. Background Art

[0002] With the acceleration of urbanization and the increase in population density, modern cities are facing increasingly severe traffic congestion problems. In order to ease the pressure of ground traffic, the development and utilization of underground space has become an inevitable trend. The construction of underground transportation systems such as subways and tunnels is becoming more and more common, forming a complex underground space network. In this context, the intersection between underground tunnels is becoming more and more common, especially in dense urban center areas. At present, the construction of underground tunnels mainly adopts the shield method. This method has the advantages of fast construction speed and little impact on the ground, but it also faces some technical challenges. Among them, the construction of close-range crossing tunnels is a particularly thorny problem. When the clear distance between the two tunnels is less than the tunnel diameter, the mutual influence during the construction process becomes particularly significant.

[0003] During shield construction, it is inevitable that the surrounding soil will be disturbed, causing ground deformation and ground settlement. This disturbance not only affects ground buildings and facilities, but also affects adjacent underground structures. In the case of upper and lower crossing, the construction of the upper tunnel will produce pressure on the lower tunnel, while the construction of the lower tunnel may cause uneven settlement of the upper tunnel. This mutual influence may cause deformation, cracking, and even collapse of the tunnel structure, seriously threatening construction safety and subsequent operation. In the prior art, commonly used treatment methods include using stratum reinforcement, adjusting excavation parameters, and compensatory grouting. However, these methods still have some limitations when dealing with upper and lower close-range crossing tunnels. The effect of stratum reinforcement is often difficult to control accurately, which may lead to over-reinforcement or under-reinforcement; although adjusting excavation parameters can reduce stratum disturbance to a certain extent, it is difficult to completely eliminate mutual influence; although compensatory grouting technology can fill gaps, it is difficult to effectively control the mechanical transmission between the two tunnels. In addition, when dealing with upper and lower crossing tunnels, the prior art often lacks a systematic solution, and it is difficult to take into account both the safety of the construction process and the stability of later operations. Especially under complex geological conditions, existing technologies cannot effectively guarantee the long-term stability and independence of the two tunnels. Summary of the invention

[0004] In view of this, the present invention provides a method for protecting the construction of intersecting shield sections, which can solve the problem of mutual influence in the construction of upper and lower close-range crossing tunnels.

[0005] The present invention is achieved in that:

[0006] The present invention provides a method for protecting and constructing intersecting shield sections, comprising the following steps:

[0007] S10. Construct an open excavation pit at the tunnel intersection, lay out bored cast-in-place piles and cap beams in the pit as the retaining structure, and set up a steel support system inside the pit;

[0008] S20. After the construction of the retaining structure is completed, the foundation pit is excavated to the designed depth, and reinforced concrete support piles and pile top beams are constructed;

[0009] S30, after the supporting piles and pile top beams are completed, a reinforced concrete protection plate is constructed to form a sheet pile structure type reinforced concrete protection structure system;

[0010] S40. After the protection structure is completed, C15 plain concrete is used to backfill to the designed elevation, and then 6% cement soil is used to backfill to the ground in layers;

[0011] S50. Set up a test section within 70 meters before the shield machine crosses the intersection to collect data on soil bin pressure, total thrust, torque, cutterhead speed, excavation speed, excavation volume and grouting volume;

[0012] S60: When the shield tunneling reaches the intersection area, the tunneling speed is controlled at 5 to 10 mm / min, and the soil bin pressure is controlled at 0.6 to 1.0 bar;

[0013] S70: During shield tunneling, synchronous grouting is carried out, with the grouting pressure controlled at 0.2 to 0.3 MPa, and mid-shield grouting is carried out within 12.4 meters before and after the intersection;

[0014] S80: After the shield passes through the intersection, a closed loop is set up within 5 meters before and after the intersection, and double-liquid slurry is used for wall grouting, and the grouting pressure is controlled at 0.3 to 0.4 MPa;

[0015] S90. Two weeks after the shield tunnel has passed, geological radar scanning is used to detect voids, and additional grouting is carried out when voids are found.

[0016] On the basis of the above technical solution, the intersecting shield section protection construction method of the present invention can also be improved as follows:

[0017] Wherein, the step S10 specifically includes:

[0018] Step 101: Survey the buildings within 30 meters around the foundation pit, set up monitoring points and collect initial data;

[0019] Step 102, level the site, measure and locate the position of the foundation pile, and use the casing burying method to locate it, with the top of the casing 0.3 to 0.5 meters above the ground;

[0020] Step 103, using a rotary drill to perform dry drilling, when drilling, first use a low speed to drill to 1 meter below the casing and then adjust to a normal speed;

[0021] Step 104: After the hole is formed, the hole depth, hole diameter and verticality are checked to ensure that the sediment at the bottom of the pile does not exceed 200 mm;

[0022] Step 105, make a steel cage, divide it into sections and number it according to the designed length, and equip it with a special bracket when hoisting it to ensure that the center line of the steel cage remains consistent when it is docked;

[0023] Step 106, pouring concrete using the conduit method, with the bottom of the conduit 0.3 to 0.5 meters from the bottom of the hole, and the storage hopper volume meeting the depth requirement for burying the conduit for the first batch of concrete;

[0024] Step 107, during pouring, check the concrete surface height and the buried depth of the conduit at any time, and the buried depth of the conduit is controlled to be 2 to 4 meters;

[0025] Step 108: Use the ring cutting method to cut off the pile head to ensure that the steel bars are not damaged.

[0026] Furthermore, the step S20 specifically includes:

[0027] Step 201, excavate the foundation pit by adopting the construction principle of layered excavation and supporting before excavation, and the excavation depth of each layer shall not exceed 0.5 meters below the bottom surface of the corresponding support;

[0028] Step 202, set up drainage ditch and water collection well, the depth of drainage ditch is 0.4 to 0.5 meters lower than the excavation surface, more than 1 meter away from the retaining piles, and the ditch bottom is set with a longitudinal slope of 0.5%;

[0029] Step 203: After the foundation pit is excavated to the designed depth, a bearing capacity test is performed, and the last 0.3 meters of earth is removed manually;

[0030] Step 204, stake out the support pile positions, and use a total station to perform positioning measurement to ensure that the pile position deviation does not exceed 50 mm;

[0031] Step 205: Drilling the support piles using a rotary drilling rig at a drilling speed of 0.5 to 1 meter per minute;

[0032] Step 206, after the hole is cleaned, the verticality and aperture are tested, and the verticality deviation does not exceed 1%;

[0033] Step 207, factory-process the steel cage, hoist it on site, and use positioning blocks to control the steel protection layer;

[0034] Step 208: Use the conduit method to pour concrete, and the buried depth of the conduit is not less than 2 meters to ensure the quality of the concrete.

[0035] Furthermore, the step S30 specifically includes:

[0036] Step 301, measuring and laying out to determine the position and elevation of the protection plate;

[0037] Step 302: Use a combined steel formwork as a protection plate formwork, and the support system uses adjustable steel pipe support, with a support spacing of no more than 1 meter;

[0038] Step 303, perform steel bar binding, the main bars are connected by straight threaded sleeves, the joints are staggered, and the distance between the two joints is not less than 35 times the diameter of the steel bar and not less than 1 meter;

[0039] Step 304, pouring concrete by layer pouring method, controlling the thickness of each layer to 30 cm, vibrating by insert vibrator, and vibrating time for 15 to 20 seconds;

[0040] Step 305, the curing period is not less than 7 days, and the temperature difference of the concrete surface is controlled within 20 degrees Celsius during the curing period.

[0041] Furthermore, the step S40 specifically includes:

[0042] Step 401, backfilling the foundation pit by layered backfilling and symmetrical compaction;

[0043] Step 402: The first floor is backfilled with C15 plain concrete, which is pumped into the foundation pit by a concrete pump, and the free fall height is controlled to be no more than 2 meters during pouring;

[0044] Step 403: After the plain concrete reaches the designed strength, cement soil is backfilled, and the thickness of each layer is 250 to 300 mm;

[0045] Step 404, compacting by combining mechanical and manual methods, in both the vertical and horizontal directions, one tamping and half tamping, and compacting each layer 3 to 4 times;

[0046] Step 405: When backfilling in sections, a step of 1:2 is left at the junction, the distance between the upper and lower layers is not less than 1 meter, and the overlapping width of rolling is 0.5 to 1 meter;

[0047] Step 406: Control the compaction coefficient of the backfill soil to be no less than 0.94, and perform density testing after each layer of backfill is completed.

[0048] Furthermore, the step S50 specifically includes:

[0049] Step 501, setting up a test section within 70 meters before the intersection, and controlling the excavation speed to 20 to 30 mm per minute;

[0050] Step 502, controlling the soil bin pressure to be between 0.15 and 0.2 MPa, and the total thrust to be between 8000 and 12000 kN;

[0051] Step 503, using a foaming agent to improve the slag soil, the foam solution is composed of 3% foam additive and 97% water, and the injection amount is 15% to 40% of the excavated soil volume;

[0052] Step 504, controlling the soil moisture content to be between 30% and 40%, and the water injection volume to be between 100 and 300 liters per cubic meter;

[0053] Step 505: Strictly control the tightening torque of the segment assembly bolts, and the segment ovality deviation does not exceed 1% of the design value.

[0054] Furthermore, the step S60 specifically includes:

[0055] Step 601, reducing the excavation speed to 5 to 10 mm / min, and controlling the soil bin pressure to 0.6 to 1.0 bar;

[0056] Step 602, adjusting the pressure of each zone of the propulsion cylinder according to the position of the retaining pile;

[0057] Step 603, strictly controlling the slag discharge volume to be between 98% and 102% of the theoretical excavation volume;

[0058] Step 604, during pile cutting and excavation, the foam injection amount is 30% of the slag, and the foam pipeline is suspended in turn in stages;

[0059] Step 605: monitor the ground settlement data every half hour and adjust the excavation parameters in time according to the monitoring results.

[0060] Furthermore, the step S70 specifically includes:

[0061] Step 701, perform synchronous grouting, and control the grouting pressure at 0.2 to 0.3 MPa;

[0062] Step 702, using the dual control standard of pressure and grouting volume, the grouting volume is calculated and determined according to the theoretical filling space;

[0063] Step 703: Zhongdun grouting uses bentonite slurry with a consistency of 10 to 20 seconds, and the grouting pressure is also controlled at 0.2 to 0.3 MPa;

[0064] Step 704: perform shield grouting within 12.4 meters before and after the intersection to ensure dense filling.

[0065] Furthermore, the step S80 specifically includes:

[0066] Step 801, setting a closed loop within 5 meters before and after the intersection, and using double-liquid slurry for back-wall grouting;

[0067] Step 802, the double liquid slurry is composed of cement slurry and water glass with a water-cement ratio of 1:1, a volume ratio of 2:1, and an initial setting time controlled within 30 seconds;

[0068] Step 803, grouting is performed from bottom to top, and the grouting pressure is controlled at 0.3 to 0.4 MPa;

[0069] Step 804: Perform secondary grouting between two closed loops every two loops, using cement slurry for grouting, and the pressure is also controlled at 0.3 to 0.4 MPa.

[0070] Furthermore, the step S90 specifically includes:

[0071] Step 901: After the shield tunnel has passed for two weeks, a geological radar is used for scanning and detection. The detection frequency is 100 MHz and the scanning range covers 3 meters of the soil around the tunnel.

[0072] Step 902: If a cavity is found, immediately perform supplementary grouting, using a double-liquid grouting process, and controlling the grouting pressure at 0.2 to 0.4 MPa;

[0073] Step 903: Keep in touch with the shield machine operation room at any time during the supplementary grouting. If abnormal phenomena such as increased soil pressure and thrust are found, stop grouting immediately and flush the pipeline;

[0074] Step 904, continue grouting operation after the abnormal phenomenon is eliminated;

[0075] Step 905: After the supplementary grouting is completed, a geological radar scan is performed again to confirm the cavity filling effect.

[0076] Compared with the prior art, the beneficial effects of the intersecting shield section protection construction method provided by the present invention are:

[0077] First, the present invention achieves effective isolation between the upper and lower tunnels by setting a reinforced concrete protective structure of sheet pile structure at the intersection of the tunnels. This structure utilizes the high rigidity characteristics of reinforced concrete to effectively transfer the load generated during the construction and operation of the upper tunnel to the lower bearing layer, greatly reducing the impact on the lower tunnel. At the same time, the impact of the construction and operation of the lower tunnel on the upper tunnel is also effectively blocked. This isolation effect is far superior to traditional stratum reinforcement methods and can better ensure the independence and stability of the two tunnels.

[0078] Secondly, the present invention adopts a systematic construction plan, including a series of steps such as foundation pit excavation, support pile construction, protection plate structure construction, and layered backfilling. This systematic plan ensures the controllability and safety of the construction process. In particular, the method of layered backfilling using C15 plain concrete and 6% cement soil not only improves the backfill quality, but also enhances the stability of the entire structural system. Compared with traditional simple backfilling, this method can better control stratum settlement and reduce the impact of later settlement on the tunnel structure.

[0079] Thirdly, the present invention adopts refined parameter control and grouting measures during the shield tunneling process. By setting up a test section to collect various tunneling parameters, reliable data support is provided for subsequent construction. In the intersection area, by strictly controlling parameters such as tunneling speed and soil bin pressure, the disturbance to the surrounding strata is minimized. At the same time, multiple grouting measures such as synchronous grouting, middle shield grouting and closed ring grouting are adopted to effectively fill the gaps generated during the shield tunneling process and further stabilize the strata. This refined control and multiple protection measures significantly improve the accuracy and safety of construction.

[0080] In addition, the present invention also adopts the method of post-detection and supplementary grouting to timely discover and deal with potential cavitation problems through geological radar scanning. This method of continuous monitoring and timely treatment provides a strong guarantee for the long-term stable operation of the tunnel.

[0081] Compared with the prior art, the solution of the present invention shows obvious progress in the following aspects:

[0082] 1. Effective isolation of upper and lower cross tunnels is achieved, greatly reducing mutual influence.

[0083] 2. Provides a systematic construction plan to improve the controllability and safety of construction.

[0084] 3. Refined parameter control and multiple grouting measures were adopted to significantly improve construction accuracy and formation stability.

[0085] 4. A post-monitoring and treatment mechanism was introduced to ensure the long-term stability of the tunnel.

[0086] In general, the solution of the present invention not only solves the problem of mutual influence in the construction of upper and lower close-range crossing tunnels, but also improves the construction efficiency and quality, and provides comprehensive technical support for the safe construction and stable operation of tunnels. BRIEF DESCRIPTION OF THE DRAWINGS

[0087] Figure 1 A flowchart of the steps of the present invention;

[0088] Figure 2 It is a schematic diagram of the reinforced foundation pit retaining structure in specific embodiment 1;

[0089] Figure 3 is a schematic diagram of a multi-layer support in specific embodiment 1;

[0090] Figure 4 This is a schematic diagram of steel support hoisting in specific embodiment 1;

[0091] Figure 5 It is a schematic diagram of backfilling in specific embodiment 1;

[0092] Figure 6 This is a schematic diagram of the reinforcement construction of the shield tunnel crossing the tunnel intersection in the specific embodiment 1;

[0093] Figure 7 This is a schematic diagram of synchronous grouting in specific embodiment 1.

[0094] Figure 8 It is a flowchart of the synchronous grouting process in specific embodiment 1;

[0095] Fig. 9 It is a schematic diagram of ground tracking grouting in specific embodiment 1;

[0096] Fig.10 This is a graph of surface settlement monitoring data during foundation pit excavation in Example 2;

[0097] Fig.11 This is a data analysis diagram of shield tunneling parameter monitoring in Example 2. DETAILED DESCRIPTION

[0098] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0099] like Figure 1 As shown, it is a flow chart of a method for protecting the intersecting shield sections provided by the present invention. The method comprises the following steps:

[0100] S10. Construct an open excavation pit at the tunnel intersection, lay out bored cast-in-place piles and cap beams in the pit as the retaining structure, and set up a steel support system inside the pit;

[0101] S20. After the construction of the retaining structure is completed, the foundation pit is excavated to the designed depth, and reinforced concrete support piles and pile top beams are constructed;

[0102] S30, after the supporting piles and pile top beams are completed, a reinforced concrete protection plate is constructed to form a sheet pile structure type reinforced concrete protection structure system;

[0103] S40. After the protection structure is completed, C15 plain concrete is used to backfill to the designed elevation, and then 6% cement soil is used to backfill to the ground in layers;

[0104] S50. Set up a test section within 70 meters before the shield machine crosses the intersection to collect data on soil bin pressure, total thrust, torque, cutterhead speed, excavation speed, excavation volume and grouting volume;

[0105] S60: When the shield tunneling reaches the intersection area, the tunneling speed is controlled at 5 to 10 mm / min, and the soil bin pressure is controlled at 0.6 to 1.0 bar;

[0106] S70: During shield tunneling, synchronous grouting is carried out, with the grouting pressure controlled at 0.2 to 0.3 MPa, and mid-shield grouting is carried out within 12.4 meters before and after the intersection;

[0107] S80: After the shield passes through the intersection, a closed loop is set up within 5 meters before and after the intersection, and double-liquid slurry is used for wall grouting, and the grouting pressure is controlled at 0.3 to 0.4 MPa;

[0108] S90. Two weeks after the shield tunnel has passed, geological radar scanning is used to detect voids, and additional grouting is carried out when voids are found.

[0109] The specific implementation methods of the above steps are described in detail below:

[0110] The specific steps of step S10 are to construct an open excavation pit at the intersection of the tunnel, and set up a retaining structure and a support system. First, investigate the buildings within 30 meters around the foundation pit, set up monitoring points and collect initial data. During construction, a retaining structure combining glass fiber reinforced piles and reinforced concrete piles is used, in which the pile diameter is 1200 mm and the spacing is 1800 mm. The support in the foundation pit adopts a steel pipe support with a diameter of 609 mm and a wall thickness of 16 mm. Before construction, the site is leveled, the position of the foundation piles is measured and positioned, and the casing is buried for positioning, with the top of the casing 0.3 to 0.5 meters above the ground. The drilling is carried out by a rotary drill for dry drilling. When drilling, it is first drilled at a low speed to 1 meter below the casing and then adjusted to normal speed. After drilling, the hole depth, hole diameter and verticality are checked to ensure that the sediment at the bottom of the pile does not exceed 200 mm. When the steel cage is made, it is divided into sections and numbered according to the designed length, and a special bracket is equipped during hoisting to ensure that the center line of the steel cage remains consistent when it is docked. Concrete pouring adopts the conduit method, the bottom of the conduit is 0.3 to 0.5 meters away from the bottom of the hole, and the storage hopper volume meets the requirements for the depth of the first batch of concrete buried conduits. During pouring, the concrete surface height and the buried depth of the conduit are checked at any time, and the buried depth of the conduit is controlled at 2 to 4 meters. The ring cutting method is used when the pile head is cut off to ensure that the steel bars are not damaged.

[0111] The specific steps of step S20 are foundation pit excavation and support pile construction. The foundation pit excavation adopts the construction principle of layered excavation, first support and then excavation, and the excavation depth of each layer shall not exceed 0.5 meters below the corresponding support bottom surface. During the excavation process, drainage ditches and water collection wells are set. The depth of the drainage ditch is 0.4 to 0.5 meters lower than the excavation surface, more than 1 meter away from the retaining piles, and a 0.5% longitudinal slope is set at the bottom of the ditch. After the foundation pit is excavated to the designed depth, the bearing capacity is tested, and the last 0.3 meters of earthwork is manually excavated. When constructing the support piles, the pile position is firstly staked, and the total station is used for positioning measurement to ensure that the pile position deviation does not exceed 50 mm. The bored pile is bored by a rotary drilling rig with a drilling speed of 0.5 to 1 meters per minute. After the hole is cleaned, the verticality and aperture are detected, and the verticality deviation does not exceed 1%. Factory processing is adopted for the production of steel cages, on-site hoisting, and the steel protection layer is controlled by positioning blocks. The conduit method is adopted for concrete pouring, and the buried depth of the conduit is not less than 2 meters to ensure the quality of concrete.

[0112] The specific steps of step S30 are the construction of the protection plate structure. First, measure and lay out to determine the position and elevation of the plate. The protection plate adopts a reinforced concrete structure, the concrete strength grade is C30, and the steel bar adopts HRB400 grade. The plate formwork adopts a combined steel formwork, and the support system adopts an adjustable steel pipe support, and the support spacing is not more than 1 meter. When tying the steel bars, the main bars are connected with straight threaded sleeves, and the joints are staggered. The distance between the two joints is not less than 35 times the diameter of the steel bar and not less than 1 meter. The concrete is poured in layers, and the thickness of each layer is controlled at 30 cm. The vibration adopts an inserted vibrator, and the vibration time is 15 to 20 seconds. The curing period is not less than 7 days, and the temperature difference of the concrete surface is controlled within 20 degrees Celsius during the curing period.

[0113] The specific steps of step S40 are backfilling the foundation pit. The backfilling of the foundation pit adopts the method of layered backfilling and symmetrical compaction, and the backfilling materials are C15 plain concrete and 6% cement soil. The first layer is backfilled with C15 plain concrete, which is pumped into the foundation pit by a concrete pump. The free fall height is controlled not to exceed 2 meters during pouring. After the plain concrete reaches the design strength, cement soil is backfilled. The thickness of each layer is 250 to 300 mm, and it is compacted by a combination of machinery and manual labor. When compacting, it is carried out in both vertical and horizontal directions, one tamping and half tamping, and each layer is compacted 3 to 4 times. When backfilling in sections, a 1:2 step is left at the junction, the distance between the upper and lower layers is not less than 1 meter, and the rolling overlap width is 0.5 to 1 meter. The compaction coefficient of the backfill soil is not less than 0.94, and the density is tested after each layer of backfill is completed.

[0114] The specific steps of step S50 are shield test section excavation. A test section is set up within 70 meters before the intersection, and various excavation parameters are collected. The excavation speed is controlled at 20 to 30 mm per minute, the soil bin pressure is 0.15 to 0.2 MPa, and the total thrust is controlled at 8000 to 12000 kN. Foaming agent is used for slag improvement. The foam solution consists of 3% foam additive and 97% water, and the injection amount is 15% to 40% of the excavated earthwork. At the same time, the moisture content of the slag is controlled between 30% and 40%, and the water injection amount is 100 to 300 liters per cubic meter. When assembling the test section segments, the bolt tightening torque is strictly controlled, and the segment ovality deviation does not exceed 1% of the design value.

[0115] The specific steps of step S60 are shield tunneling in the intersection area. The tunneling speed is reduced to 5 to 10 mm per minute, and the soil bin pressure is controlled at 0.6 to 1.0 bar. The pressure of each partition of the propulsion cylinder is adjusted according to the position of the retaining pile, and the slag output is strictly controlled between 98% and 102% of the theoretical excavation volume. The foam injection volume during pile cutting and tunneling is 30% of the slag, and the foam pipeline is suspended in stages. The ground settlement data is monitored every half an hour, and the tunneling parameters are adjusted in time according to the monitoring results.

[0116] The specific steps of step S70 are grouting construction during shield tunneling. Synchronous grouting is carried out synchronously with shield tunneling, and the grouting pressure is controlled at 0.2 to 0.3 MPa. The pressure and grouting volume dual control standard is adopted, and the grouting volume is determined according to the theoretical filling space calculation. The middle shield grouting uses bentonite slurry with a consistency of 10 to 20 seconds, and the grouting pressure is also controlled at 0.2 to 0.3 MPa. The middle shield grouting is carried out within 12.4 meters before and after the intersection to ensure dense filling.

[0117] The specific steps of step S80 are closed loop grouting. A closed loop is set within 5 meters before and after the intersection, and double liquid slurry is used for wall back grouting. The double liquid slurry is composed of cement slurry and water glass with a water-cement ratio of 1:1, a volume ratio of 2:1, and the initial setting time is controlled within 30 seconds. Grouting is carried out from bottom to top, and the grouting pressure is controlled at 0.3 to 0.4 MPa. Secondary grouting is carried out every two rings between the two closed loops, using cement slurry grouting, and the pressure is also controlled at 0.3 to 0.4 MPa.

[0118] The specific steps of step S90 are post-detection and supplementary grouting. Two weeks after the shield passes, a geological radar is used for scanning and detection. The detection frequency is 100 MHz, and the scanning range covers 3 meters of the soil around the tunnel. If a cavity is found, supplementary grouting is carried out immediately, using a double-liquid grouting process, and the grouting pressure is controlled at 0.2 to 0.4 MPa. Keep in touch with the shield machine operating room at any time during supplementary grouting. If abnormal phenomena such as increased soil pressure and increased thrust are found, stop grouting immediately and flush the pipeline. Continue grouting operations after the abnormal phenomena are eliminated. After the supplementary grouting is completed, perform a geological radar scan again to confirm the cavity filling effect.

[0119] Specifically, the principle of the present invention is: from the perspective of structural force principle, the sheet pile structure type reinforced concrete protection structure adopted by the present invention fully utilizes the high rigidity characteristics of the reinforced concrete structure. The sheet pile structure penetrates into the bearing layer through the pile foundation, forming a reliable vertical bearing system. At the same time, through the connection of the crown beam and the protection plate, a spatial structural system with strong integrity is formed. This structural form can effectively disperse and transfer the load generated by the upper tunnel, avoiding the direct effect of the load on the lower tunnel.

[0120] In terms of the stratum control principle, the present invention adopts the idea of ​​"using rigidity to control flexibility". By constructing a high-rigidity protective structure in the soft stratum, the stress distribution state of the stratum is changed. The setting of the sheet pile structure forms a relatively rigid "bearing bridge" in the intersection area, which changes the load transfer path between the upper and lower tunnels and avoids the direct impact of the upper tunnel on the lower tunnel.

[0121] In terms of construction process principles, the present invention adopts the principle of "support first, then dig, layered construction, and strict control". Through a reasonable construction sequence arrangement, each construction stage is ensured to be carried out under a controllable state. Especially in the shield tunneling process, the optimal construction parameters can be obtained through the setting of the test section, providing a scientific basis for subsequent construction.

[0122] In terms of the principle of stratum reinforcement, the multiple grouting system adopted in the present invention realizes all-round reinforcement of the stratum. Synchronous grouting can fill the gaps at the shield tail in time, middle shield grouting can strengthen the support of the surrounding rock, and secondary grouting can further improve the stratum properties. The synergistic effect of multiple grouting not only fills the gaps generated during the construction process, but also improves the overall strength and stability of the stratum.

[0123] In terms of monitoring and control principles, the present invention has established a monitoring system including stratum deformation, structural stress, construction parameters, etc. Through real-time analysis and feedback of monitoring data, abnormal conditions in the construction process can be discovered in time and corresponding adjustment measures can be taken. This "monitoring-guided construction" method ensures the controllability and safety of the construction process.

[0124] In general, the technical solution of the present invention realizes the safe construction of the upper and lower close-distance cross tunnels through reasonable structural design, scientific construction technology, effective reinforcement measures and a complete monitoring system. The various technical links cooperate with each other and are organically unified to form a complete technical system, providing reliable technical support for solving similar engineering problems.

[0125] A specific embodiment 1 of the present invention is provided below:

[0126] 1. Construction Preparation

[0127] (1) Investigate the buildings within 30m of the foundation pit, and prepare in advance the layout of monitoring points, initial data testing, and debugging of monitoring instruments for the foundation pit, surrounding buildings, and ground and underground pipelines, so that monitoring work is ready.

[0128] (2) Formulate a special plan for emergency measures. The relevant emergency construction special plan should be approved by the property owner and relevant departments; establish a complete early warning mechanism and implement a three-level early warning management system; when the monitoring results exceed the warning value, take immediate measures to control the settlement control value of the tunnel shield construction within the required range.

[0129] 2 Open excavation foundation pit construction

[0130] 1. The reinforced foundation pit retaining structure adopts the form of pile row + internal support support, such as Figure 2 As shown, the piles are reinforced concrete, glass fiber reinforced piles are used in the tunnel passage area, the pile diameter is 1200mm, the distance between piles is 1800mm, and the support in the foundation pit is Φ609 (wall thickness t=16mm) steel pipe support. Piles are set on both sides of the lower tunnel line, with a pile diameter of 1200mm and a distance between piles of 3000mm. After excavation to the designed depth of the foundation pit, a C15 plain concrete backfill layer is first applied under the slab and on both sides of the piles, and then the pile top beam and reinforcement plate are applied.

[0131] 2. Construction methods of piles of retaining structure and pile foundation of protective structure

[0132] (1) The coordinates of the pile position should be placed 20 cm to 30 cm outside the foundation pit to avoid the situation where the retaining piles invade the limit. After the support piles are bored, concrete needs to be poured to the designed elevation, and the hollow part of the support piles should be backfilled with soil to the original ground.

[0133] (2) Casing burial: First, fill the drilling platform and compact it. On the platform, accurately measure and determine the longitudinal and transverse axes of the pile. Then, hoist the casing, lower it to the bed, and hang a hammer ball to measure its inclination to ensure that it is not greater than 1%. Backfill clay around the casing and tamp it. The casing is buried by manual excavation and backfilled with clay. The top of the casing should be 0.3 to 0.5 m above the ground.

[0134] (3) Drilling: According to geological conditions, the bored pile adopts rotary drilling and dry drilling. First, drill slowly at low gear until 1m below the casing, then adjust to normal speed. During the drilling process, adjust the drilling speed and drilling pressure according to the changes in the soil layer.

[0135] (4) Hole inspection: When the drilling depth reaches the design requirement, a borehole inspection device is used to check the hole depth, hole diameter and verticality.

[0136] (5) Hole cleaning: After the hole is formed, use a rotary drilling rig with a flat-bottom drill bit to clean the hole to ensure that the sediment at the bottom of the pile does not exceed 200 mm.

[0137] (6) Fabrication and installation of steel cage: The steel cage is manufactured in a steel processing plant. It is manufactured in whole sections or sections according to the length of the pile. The steel cage of each pile is divided into sections according to the designed length and numbered to ensure that adjacent sections can be paired and tied on the tire frame. The steel cage is equipped with a special bracket when it is hoisted. It is transported to the site by a flatbed truck and lowered at the hole mouth by a car crane. Before lowering, the verticality of the steel cage is checked to ensure that the center lines of the upper and lower steel cages are consistent when they are connected. The steel cage is hoisted into the hole as a whole by a crane. When the bottom of the steel cage reaches the designed depth, two I10 steel poles are used to place the steel cage on the casing.

[0138] (7) Pouring underwater concrete: Before pouring concrete, the conduit must be tested for watertightness, pressure bearing and joint tensile strength. After passing the test, it is spliced ​​in sections and hoisted into the hole by a crane to form a whole. After the steel cage is in place and passed the inspection, the conduit is lowered, and the funnel, storage hopper and water stopper are installed. The bottom of the conduit is 0.3 to 0.5m away from the bottom of the hole. The volume of the storage hopper must meet the requirements for the depth of the conduit buried in the first batch of concrete poured (not less than 1m). When pouring concrete, use a measuring rope to check the concrete surface height and the buried depth of the conduit at any time, and strictly control the buried depth of the conduit to prevent leakage of the conduit or the pipe being buried too deep and unable to be pulled out, resulting in broken piles. The buried depth of the conduit should take into account the thickness of the scum on the concrete surface, and use a steel pipe sampling box to test its thickness in advance. The depth of the conduit buried in the concrete is generally controlled to be 2 to 4m. Detailed records should be kept during the concrete pouring process.

[0139] (8) Inspection of pile head and pile foundation: The top surface of concrete pouring should be about 0.8 to 1m higher than the designed pile top. The concrete pile head should be chiseled to the designed elevation by ring cutting method 3 to 5 days after pouring. The pile body concrete quality inspection should be carried out after the retaining pile is completed. The structural integrity of the rotary bored pile should be tested by low strain dynamic testing method. Some rotary bored piles designed as permanent structures shall be tested 100%.

[0140] 3. Construction method of crown beam and concrete slab support

[0141] (1) The construction of crown beams and concrete slab supports connects all the enclosure structures into a whole, which can improve the anti-overturning ability of the entire structure and facilitate the construction of the support system.

[0142] (2) Trench excavation: After the retaining piles reach the designed strength, trench excavation is carried out according to the excavation boundary determined by the surveying personnel. An excavator is used in conjunction with manual excavation to the bottom of the crown beam. During and after the excavation, attention should be paid to protecting the trench slope.

[0143] (3) Circumferential cutting of pile head: During construction, a 20 cm wide strip-shaped circular area is set above the pile top position required by the design. A cutting machine is used to perform circular cutting along the line using the double-sided circular cutting method. The cutting thickness is slightly less than the thickness of the concrete protective layer to prevent damage to the pile foundation steel bars.

[0144] (4) Pile head removal: After the cutting is completed, the concrete at the ring-cut part is chiseled out to form a gap to expose the steel bars. Use a breaker to peel off the steel bar protective layer on the upper side of the gap to expose the steel bars. Be careful not to damage the steel bars during construction. The steel bars are slightly bent outward (no more than 30 degrees) to facilitate construction. The pile foundation test is carried out using the low-strain reflection wave method or the sound wave transmission method. After the age of the concrete of the pile body reaches 14 days, the concrete strength of the pile body should not be less than 70% of the design strength and should not be less than 15MP before the pile foundation test can be carried out.

[0145] (5) Installation of steel bars and embedded parts: Embed the steel bar head at the edge of the groove to fix the formwork. Verify the bottom elevation of the crown beam and the length of each foundation pile embedded in the crown beam, and trim the bottom surface. The top of the foundation pile above the bottom of the crown beam to the design elevation range should show the fresh concrete surface. The length of the foundation pile embedded in the crown beam and the length of the main steel bar anchored in the crown beam meet the design requirements. At the same time, check the test report of the steel bar raw material and welded parts. The construction of steel bars can only be carried out after the professional supervision engineer has checked and passed. The crown beam steel bar is made and formed in the processing plant and transported to the site for installation. When tying the steel bars, the spacing of the steel bars and the lap length (the main bars are connected with straight threaded sleeves) must meet the requirements of the specifications; the connection joints of the stress-bearing steel bars should be set at the place with smaller internal forces and staggered. The distance between the two connection joints must be greater than 35 times the diameter of the steel bar and not less than 100cm. The connection joints in the tension zone of the bending member shall not be greater than 50%, and in the axial tension member shall not be greater than 25%.

[0146] (6) Formwork installation: Formwork support is constructed by combining formwork scaffolding pipes and φ16 tension steel bars. Double-row scaffolding is set up around the crown beam foundation using φ48 steel pipes for formwork construction. The vertical poles are anchored into the soil, and the crossbars press the upper edge of the formwork to prevent the formwork from floating up due to lateral pressure during concrete pouring. The support vertical poles are sunk into the base soil with a hammer. The vertical poles sunk into the soil must be stable to prevent horizontal slippage during concrete pouring.

[0147] (7) Concrete pouring: The free fall height of the pouring shall not exceed 2m. If it is higher than 2m, a chute shall be used to prevent the concrete from segregating. Concrete shall be poured in horizontal layers and vibrated while pouring. The thickness of the poured concrete layers shall be about 30cm.

[0148] (8) Formwork removal: The formwork can be removed only after the concrete strength of the crown beam reaches 2.5 MPa. Be careful when removing the formwork and do not damage the crown beam concrete that has been poured.

[0149] (9) Concrete curing: Cover the concrete surface with a plastic film that keeps it moist, and sprinkle water to ensure that the concrete surface is always moist. The curing period is no less than 7 days. During the curing period, strengthen the temperature control of the concrete to prevent the surface temperature of the concrete from changing due to environmental factors. The temperature difference between the concrete core and the surface, and between the surface and the environment is controlled within 20°C.

[0150] (10) Trench backfilling: After the concrete reaches the designed strength, the trench facing the soil side shall be backfilled. Before backfilling, use a water pump to drain the accumulated water in the foundation pit and remove all debris from the bottom of the trench. The backfill must be made of plain soil without any domestic or construction waste; there must not be any stones larger than 10 cm, and the backfill soil must be free of silt and wet mud.

[0151] 4. Construction method of foundation pit drainage

[0152] (1) Effective and reasonable drainage measures are one of the effective measures to reduce the risk of deep foundation pit construction. According to the surrounding environmental conditions and geological conditions of this project, the soft soil and Chengdu clay in the area have small water volume, poor water richness, low water permeability, and a general permeability coefficient of 0.001m / d; mudstone has small water volume, poor water richness, low water permeability, and a general permeability coefficient of 0.44m / d (average value). During the construction period, the solution of water stopping outside the pit + drainage inside the pit was adopted.

[0153] (2) Construction method of drainage outside the pit: The reinforced vertical shaft adopts the scheme of forming a water-stop curtain by constructing plain concrete piles and retaining piles. A retaining wall with a height of 1m and a thickness of 0.25m is set on the crown beam around the foundation pit to protect the foundation pit and block water. The following is a schematic diagram:

[0154] (3) Pit drainage construction method: set up an open drainage ditch in the foundation pit, set up a water collection well at each corner of the reinforced vertical shaft, so that water is collected in the water collection well, and then pumped out of the foundation pit with a water pump. The depth of the drainage ditch should always be kept 0.4-0.5m lower than the excavation surface, at least 1m away from the retaining piles, and the width should not be less than 0.3m. The side slope of the ditch is 1:1, and the bottom of the ditch is set with a longitudinal slope of 0.5% to prevent water flow from being blocked; the water collection well should be 0.5-1.0m lower than the drainage ditch, and deepened as the foundation pit is excavated. The cross-section of the water collection well is 0.8×0.8m, and the bottom of the well should be filled with 20cm gravel or pebbles. Use a water pump to extract and drain to the sedimentation tank. The water pump tap should be wrapped with a filter to prevent mud from entering the water pump.

[0155] 5. Steel support construction method

[0156] (1) Figure 3As shown in the figure, the foundation pit adopts bored cast-in-place piles plus internal supports as the foundation pit retaining structure. Except for the first steel support directly supported on the crown beam at the top of the pile, the rest are equipped with steel purlins. Concrete slab supports are installed at the corners of the crown beam at the same time, and the other three support corners are all equipped with steel plate supports. In order to ensure that the diagonal brace is stressed, triangular shear blocks are set on the steel purlins corresponding to the diagonal brace to ensure that the stress surface is orthogonal to the diagonal brace.

[0157] (2) Figure 4 As shown, the support erection process method: the position of the steel support is set out by a dedicated person. Before installing the steel support, first install the triangular support frame for fixing the steel purlin on the enclosure structure, then install the purlin and the tray for the steel pipe support, and place the cross line of the steel pipe support on the tray. Pour 6cm thick C20 fine stone concrete between the steel purlin and the patent pile and tamp it to make the patent pile evenly stressed, and only after the strength of the fine stone concrete reaches 80% of the design strength, it is allowed to apply the prestress of the steel support. The installation of the steel support closely follows the progress of the foundation pit excavation, and the steel pipe is assembled on the spot in the leveled site, lifted and placed in place by a car crane, and lowered into the foundation pit. When the foundation pit is excavated to 0.5m below the elevation of the support centerline, the excavation must be stopped and the steel pipe support must be erected in time. When installing the steel pipe, control the axis position to prevent the steel pipe from being installed in place. Each pipe support is provided with a flexible head jack support and a load-bearing corbel at one end. After installation, the middle part of the steel pipe support is hoisted by a crane to resist the deflection caused by the deadweight of the steel pipe support. Then, prestress is applied to the support with an engineering jack and a hydraulic pump. The prestressing should be applied in stages and repeatedly. Then, steel wedges are added to the reserved gap between the pipe end and the purlin to tighten it. Finally, the jack is loosened and removed.

[0158] (3) Support protection: During the excavation of the foundation pit, it is necessary to prevent the excavation machinery and lifting operations from colliding with the support system. During the construction process, strengthen monitoring. If the axial force of the steel pipe cross brace is too large and the cross brace deflection is close to the allowable value, take measures such as adding temporary vertical support to prevent the cross brace from being too large, ensure the stability of the steel support force, and ensure the safety of the foundation pit.

[0159] (4) Technical measures for support removal: The process of dismantling the support system is actually the process of "reversing" the support, that is, transferring the lateral soil pressure borne by the steel pipe cross brace to the permanent support structure or other temporary support structures. The steel support is dismantled in sections from bottom to top. The steel support can only be removed when the layered backfill under the steel support reaches 0.5m below the axis of the steel support. During dismantling, the axial force is released in stages to avoid excessive instantaneous prestress release that may cause local deformation and cracking of the structure. At the same time, the top displacement of the crown beam and the lateral pressure of the retaining pile core are monitored.

[0160] 6. Foundation pit excavation construction method

[0161] (1) Excavation of the foundation pit can only be carried out after the crown beam and the retaining piles have reached the designed strength. The excavation of the foundation pit shall be carried out in accordance with the principles of "longitudinal segmentation, vertical stratification, middle trenching, horizontal block division, support before excavation, protection while excavation, timely closure, and adequate monitoring".

[0162] (2) When excavating the soil layer of the first and second supports, the support of this section shall be installed and prestressed within 12 hours; the excavation surface of each layer of earthwork shall not be lower than 0.5m below the bottom surface of the corresponding steel support. The excavation of the foundation pit shall be carried out from top to bottom. The excavation depth shall be strictly in accordance with the elevation given in the design drawing, and over-excavation is strictly prohibited. When the foundation pit is excavated to 0.3m above the base, the bearing capacity of the base shall be tested in time. After verifying that it meets the design requirements, the remaining earthwork shall be removed manually. After excavating to the design elevation, the foundation pit shall be leveled immediately, and the C15 plain concrete backfill layer shall be applied under the reinforcement plate and on both sides of the support piles in time; when excavating earthwork, sufficient transportation vehicles and construction machinery shall be prepared to ensure that each layer of earthwork excavation is completed within the time required by the specification, so as to achieve the effect of "fast support and fast excavation, protection as excavation is carried out", and reduce the exposure and deformation time of the foundation pit.

[0163] (3) Wet spraying is used for shotcrete construction after foundation pit excavation. Early-strength concrete is used for shotcrete, ensuring that it can reach 10MPa within 24 hours. The order of spraying operation: when spraying, first turn on the liquid quick-setting agent pump, then turn on the air, and then feed the material, with good coagulation effect, small rebound, and moist and glossy surface as the standard.

[0164] 3-board construction

[0165] 1. The slab is constructed when the C15 plain concrete is backfilled to the designed elevation under the slab, and the slab is constructed simultaneously with the pile cap beam at the bottom of the foundation pit.

[0166] 2. Concrete pouring is done by pumping with a ceiling pump. During the pouring process, attention should be paid to the fact that the concrete pouring drop should not be greater than 2m. Otherwise, a string tube should be added to prevent concrete segregation, which will affect the quality of concrete. The construction process is the same as that of the crown beam and concrete slab support.

[0167] 4 Foundation pit backfill construction

[0168] 1. If Figure 5 As shown in the figure, backfilling begins after the structural concrete strength reaches the design requirements and the external waterproofing construction is completed to ensure that the top plate waterproofing layer is not damaged during the backfilling process. The backfilling sequence is the same as the structural construction sequence. The bottom layer backfill uses C15 plain concrete, which is poured by sky pumping. After backfilling to the design elevation, 6% cement soil is used to backfill to the original ground.

[0169] 2. The backfill of foundation pit should be layered and compacted horizontally by machinery. The thickness after compaction should be determined according to the compaction machinery and should not be greater than 0.3m. Both sides of the structure should be filled horizontally and symmetrically at the same time.

[0170] (1) Before filling, the foundation concealed works shall be inspected and accepted, and records shall be made. After being evaluated as qualified by all participating construction units, filling can be carried out. Before filling, debris shall be cleaned up and stagnant water shall be removed.

[0171] (2) The backfill material is 6% cement soil. Backfill construction must be layered and compacted, with each layer 250-300mm thick. Construction personnel place horizontal elevation lines on the side walls and measure and release backfill elevation control lines based on the layered backfill thickness, thereby controlling the elevation and thickness of the backfill soil. Backfilling should be carried out symmetrically on two or four sides at the same time, and the height difference of the backfill on both sides should be well controlled. Compaction is carried out by combining machinery and manual labor. Where machinery can be used, machinery will be used for compaction, and where machinery cannot enter, manual tamping machines will be used for compaction.

[0172] 3. Spread the soil and flatten it

[0173] (1) Calculate the amount of soil to be used based on the thickness of each layer of backfill soil and spread it evenly. For wide backfill areas, use elevation piles or small lines to control the thickness and flatness of the backfill soil.

[0174] (2) The thickness of each layer is 250-300mm. When backfilling in sections, the height-to-width ratio of the steps at the junction should be 1:2, and should not be greater than 1:2. The junctions of the layers should be staggered, and the distance between the upper and lower layers should not be less than 1m. The overlapping width of the rolling should be 0.5-1m.

[0175] (3) The overlap between backfill sections that are not carried out simultaneously shall not form steep slopes. The compacted layer should be left in a stepped shape, and the width of the steps should be greater than twice the height.

[0176] 4. Compacting: The backfill soil must be compacted immediately after being leveled. The compaction should be carried out in both the longitudinal and transverse directions. One compaction is half a compaction, and the compaction is connected. The compaction position should be pressed on the gap of the previous compaction position. The tamping machine compacts each layer 3 to 4 times. The compaction coefficient of the backfill soil should not be less than 0.94. If the density still does not meet the requirements after inspection, it should continue to be compacted until it meets the requirements. The compaction should start from the surroundings and then tamp towards the middle.

[0177] 5. Check the density: The density of each layer of backfill soil after backfilling and compaction should be tested in accordance with the specifications. Only when the requirements are met can the next layer of backfilling be carried out.

[0178] 5Tunnel shield construction

[0179] 1. If Figure 6 As shown, before the shield machine passes through the tunnel intersection, the shield machine guidance is reviewed and relevant information is collected, such as design drawings, construction plans, monitoring data, foundation pit acceptance information, etc.

[0180] 2. Test section excavation

[0181] (1) Parameters The 70m section before the tunnel intersection is set up as a shield tunneling test section. The main parameters collected in the test section before the underpass include: soil bin pressure, total thrust, torque, cutter head speed, excavation speed, excavation volume (including excavation weight and volume), and grouting volume. The relationship between slag improvement and slag temperature control is established to establish a balanced excavation relationship, obtain the tunnel settlement law, and summarize the test section to provide a basis and reference for the formal underpass.

[0182] (2) Tunneling attitude control in the test section: The normal tunneling speed is controlled at 20-30 mm / min. When the shield machine attitude deviates greatly, the tunneling speed is controlled at 20 mm / min. The deviation correction concept of "small amount and multiple times" is implemented, and the deviation correction is timely. The deviation correction amount of the shield machine does not exceed 4 mm / ring at a time to reduce the disturbance to the stratum.

[0183] (3) Muck improvement technology: By improving the fluidity of the slag, the cut slag can enter the soil bin smoothly and quickly, and it is conducive to the smooth discharge of the screw conveyor. When crossing the tunnel, use high-quality foaming agents and other improvement materials. Specifically: the use of foaming agents, the foam is injected through the foam system on the shield machine. The composition of the foam is generally as follows: ① the composition of the foam solution: 3% foam additives, 97% water; ② the foam composition: 90-95% compressed air and 5-10% foam solution mixed. The injection amount of foam can be calculated according to the site conditions, the excavation volume and the actual slag volume: generally 15% to 40% of the slag volume. And adjust the water injection parameters according to the water content of the mudstone, the slag water content is controlled at 30-40%, and the water injection volume is controlled at 100-300L / m3. In moderately weathered mudstone, prevent the cutter head from producing mud cakes and reduce the cutter head torque. The slag is improved by injecting water and foam into the cutter head surface and the soil bin respectively. If necessary, foam can be injected into the screw conveyor. At the same time, a combination of roller cutters and tooth cutters is used to cut mudstone to reduce the generation of mud cakes. When excavating in water-rich strata, the main thing is to prevent water gushing, prevent gushing, reduce the torque of the cutter head, inject bentonite into the cutter head surface, soil compartment and screw conveyor, and increase the amount of bentonite injected into the screw conveyor to facilitate the formation of soil plug effect on the screw conveyor to prevent gushing. The amount of bentonite added should be determined according to the specific situation.

[0184] (4) Test section segment assembly: After the segments are affixed with gaskets, they can be hoisted down the tunnel for use only after being inspected by a dedicated person (position, model, bonding firmness, etc.). Before assembling the segments, the surface of the previous lining ring should be cleaned. During assembly, the pressure and stroke of the shield thrust hydraulic cylinder should be controlled, and the shield posture and excavation surface should be kept stable. According to the segment position and assembly sequence, the segments are assembled into rings one by one. The tightening torque of the segment connection bolts meets the design requirements. After the segment is assembled and removed from the shield tail, the segment bolts should be tightened in time. After assembly, the lining rings that have been assembled into rings should be spot checked for ovality.

[0185] (5) To ensure the smooth progress of the project construction, the tunneling management of the shield in the test section shall be strengthened, and the tunneling parameters shall be further optimized according to the geological conditions and the thickness of the cover soil; during the advancement process, the advancement direction shall be strictly controlled, and the construction measurement results shall be constantly checked with the calculated three-dimensional coordinates and adjusted in time; during the shield tunneling process, the slope shall not change suddenly, and the change of the tunnel axis and the angle shall not exceed 0.4%. The entire shield tunneling construction process shall be strictly controlled. The engineering and technical personnel shall correctly issue the tunneling instructions for each shift according to the various survey and measurement data information such as geological changes, tunnel burial depth, ground load, surface settlement, shield machine posture, cutter head torque, jack thrust, etc., and track and adjust them in real time. The shield machine operator shall strictly follow the instructions and operate carefully. The initial small deviation shall be corrected in time, and the shield machine shall be prevented from "snake" as much as possible. The shield machine shall correct the deviation by no more than 4mm / ring at a time to reduce the disturbance to the stratum.

[0186] (6) Set up a tunneling test section 70 meters before the tunnel intersection, and select the optimal tunneling parameters for the tunnel by monitoring the ground settlement. The main parameters collected in the test section before the tunneling include: soil bin pressure, total thrust, torque, cutter head speed, tunneling speed, excavation volume (including excavation weight and volume), and grouting volume. Clarify the relationship between slag improvement and slag temperature control to establish a balanced tunneling relationship, obtain the tunnel settlement law, and summarize the test section to provide a basis and reference for the formal crossing of the tunnel intersection.

[0187] (7) When the shield machine is advancing in a curved section, various construction parameters are adjusted in a timely manner based on the information data on the advancement speed, excavation volume and stratum deformation, so as to adjust the earth pressure balance value and grouting volume to the optimal state for curved advancement in the shortest possible time.

[0188] 3. Grouting construction

[0189] (1) Synchronous grouting: Figure 7 As shown, synchronous grouting is carried out simultaneously with shield excavation. Through the synchronous grouting system and the built-in grouting pipe at the tail of the shield, the shield is pushed forward to form a gap at the tail of the shield, as shown in the figure below. Grouting can be controlled automatically or manually according to needs. The automatic control method is to pre-set the grouting pressure, and the control program automatically adjusts the grouting speed. When the grouting pressure reaches the set value, the grouting stops automatically. The manual control method is to manually adjust the grouting flow, speed, and pressure at any time according to the excavation situation. The "dual control" standard of pressure and grouting volume should be adopted during grouting, and the synchronous grouting pressure should be controlled at 0.2~0.3Mpa. After each grouting is completed, the grouting pipeline should be cleaned in time to prevent blockage and abnormal pressure. The specific process is as follows Figure 8 shown.

[0190] (2) Middle shield grouting: In the special section where the shield passes through the tunnel intersection, plastic or inert slurry is injected synchronously during the excavation process through the middle shield grouting hole to compensate for the stratum loss in time, so as to reduce the disturbance to the surrounding soil and fill the building gap of the shield construction in time and effectively. During the shield crossing process, the shield excavation parameters must be strictly controlled, and the middle shield grouting is completed through the middle shield grouting hole. Bentonite is used for middle shield grouting, and the consistency of bentonite is 10-20s. The middle shield grouting section ranges from 12.4m before and after the tunnel intersection, and the grouting pressure is controlled at 0.2-0.3Mpa to ensure dense filling.

[0191] (3) Secondary grouting: When the shield passes through the reinforced foundation pit, a porous reinforced segment is used, which is conducive to the later grouting of the shield and ensures that the slurry behind the segment wall is full. A closed loop is set 5m before and after the shaft. The closed loop uses double liquid slurry for grouting behind the wall. The grouting method is from bottom to top, and the grouting pressure is controlled at 0.3-0.4Mpa. After the closed loop is completed, cement slurry is used for secondary grouting every two rings between the two closed loops, and the grouting pressure is controlled at 0.3-0.4Mpa. Two weeks after the shield passes, a geological radar scan is performed to detect whether there is a cavity. If there is a cavity, three groutings are required.

[0192] (4) Tracking grouting: Fig. 9 As shown in the figure, when the settlement rate of the stratum is large, it is necessary to carry out ground tracking grouting in time after finding the stratum cavity by geological radar scanning. Ground tracking grouting is carried out at least 4 rings behind the shield tail and is carried out when the shield machine is advancing. When the shield machine stops, the pipe should be washed and grouting should be stopped immediately to prevent the slurry from wrapping the shield body and affecting the subsequent excavation. When the shield machine is advanced again, continue grouting, and the grouting pressure should be controlled at 0.2-0.4Mpa. Keep in touch with the shield machine operation room at any time during the grouting process. If the shield machine has abnormal phenomena such as increased soil pressure and increased thrust, the grouting should be stopped immediately and the hole should be washed. After the shield machine is excavated forward normally, continue grouting; if the settlement rate is small, ground tracking grouting is carried out at least 10m behind the shield tail, and the final grouting pressure is about 1Mpa. Keep in touch with the shield machine operation room at any time during the grouting process to confirm that the grouting does not affect the excavation. The main parameters of double liquid slurry are: the water-cement ratio of cement slurry is 1:1, the volume ratio of cement slurry and water glass is 2:1, and the initial setting time is within 30 seconds. The setting time of double liquid slurry can be adjusted by adjusting the magnesium content or the water-cement ratio of cement slurry. When the tracking grouting point is more than 15m away from the shield tail, the setting time of the slurry can be adjusted to about 60 seconds.

[0193] 4. Management of shield tunneling through backfill section

[0194] (1) When the subway tunnel is passing through, the distance between the subway tunnel and the fiberglass reinforcement pile is small. The construction process should be monitored to ensure that the construction of the retaining piles and fiberglass reinforcement meets the design requirements. At the same time, during the shield tunneling, the excavation and grouting parameters should be controlled according to the following requirements to avoid the occurrence of voids and floating of subway segments during the subway shield tunneling, so as to ensure the smooth passage of the shield tunnel.

[0195] (2) When the reinforced foundation pit intersects with the subway tunnel, the cutterhead is unevenly loaded when the shield passes through. The excavation speed needs to be slowed down and controlled within 5 to 10 mm / min. The pressure of each zone of the thrust cylinder should be adjusted in time according to the position of the retaining piles to avoid deviation in the posture of the shield machine.

[0196] (3) During pile cutting and excavation, slag discharge is the key point of control. Due to the slow excavation speed, the soil pressure of the foam system continues to rise when the air intake is extremely small. The foam injection volume is 30% of the slag soil, and the foam pipeline is suspended in stages. The slag discharge is counted according to the cylinder stroke, and the slag discharge volume is controlled to be 69.6m3 and the slag discharge weight is 131.3t. Combined with the slag discharge volume and weight data of the test section, it is strictly forbidden to exceed the volume.

[0197] (4) During the crossing process, the soil bin pressure was controlled at 0.6-1.0 bar. The optimal parameters were selected according to the excavation conditions of the test section and the soil bin pressure was strictly controlled.

[0198] (5) Optimize the synchronous grouting mix ratio to make the mortar reach the initial setting state as soon as possible. Ensure that the gap behind the dense segment is filled according to the slurry mix ratio during the bearing pile foundation. The synchronous grouting pressure is controlled at 0.2-0.3MPa, and the synchronous grouting volume is controlled at 5.2-7.3m3. The optimal grouting pressure and grouting volume are selected according to the summary parameters of the test section.

[0199] (6) Before arriving at the retaining piles, the monitoring personnel set up the instruments and monitor the ground settlement data every half an hour. The monitoring change data and the vibration of the ground structure during the pile foundation cutting process are fed back to the main engine room, and the soil pressure value and grouting volume in the hole are adjusted.

[0200] (7) During tunnel shield construction, the passage of heavy-loaded vehicles transporting segments and slurry will cause tunnel vibration. It is recommended that the shield be stopped while it is passing through the reinforced foundation pit to avoid tunnel settlement caused by vibration.

[0201] (8) Before the shield machine passes through the foundation pit, manual re-measurement is carried out to verify the distance between piles when the shield machine passes through the foundation pit, which is used to guide the attitude control of the shield machine when passing through. When the shield machine passes through the backfill area, the excavation attitude must be strictly controlled and the principle of "frequent correction and small correction" must be strictly followed. The shield machine's correction amount at one time shall not exceed 4mm / ring to reduce disturbance to the stratum.

[0202] A specific embodiment 2 of the present invention is provided below, and the specific implementation methods of the steps in this embodiment 2 are described as follows: The specific implementation method of step S10 is to construct an open excavation foundation pit at the intersection of the tunnel, and to arrange bored cast-in-place piles and crown beams in the foundation pit as retaining structures, and to set up a steel support system inside the foundation pit. The purpose of this step is to construct a foundation pit support system to ensure stability and safety during the foundation pit excavation process. First, a total station is used to locate and lay out the foundation pit, and coordinate transformation and error adjustment are performed based on the least squares method to ensure the accuracy of the foundation pit position. The coordinate transformation adopts the seven-parameter method, and the transformation model is: x2=x1+Δx+mX1+∈ z Y1-∈ y Z1,y2=y1+Δy-∈ z X1+mY1+∈ x Z1,z2=z1+Δz+∈ y X1-∈ x Y1+mZ1, where x1, y1, z1 are the coordinates of the original coordinate system, x2, y2, z2 are the coordinates of the target coordinate system, Δx, Δy, Δz are the translation parameters, and m is the scale factor, ∈ x ,∈ y ,∈ z Secondly, bored pile construction is carried out, with a pile diameter of 1200 mm and a pile spacing of 1800 mm. A rotary drilling rig is used to drill holes. When making the steel cage, stress-strain calculation is used to determine the steel configuration. The steel cage calculation model is: Where [σ] is the allowable stress, σ x , σ y is the principal stress, τ xy is the shear stress. The concrete strength grade is C30, and the concrete elastic modulus is calculated using Besson's Poisson's ratio: Where E is the elastic modulus, σ is stress, ε is strain, F is the force, A is the cross-sectional area, Δl is the deformation, and l is the original length. The cross-sectional size of the crown beam is 1000 mm × 1200 mm. The finite element method is used for structural calculation to determine the reinforcement scheme. Finally, a steel support system is set up. The support uses a Φ609 mm steel pipe with a wall thickness of 16 mm. The support spacing is 3000 mm. The critical buckling force of the support is calculated based on the elastic stability theory: P cr =π 2 EI / (μl) 2 , where P cr is the critical buckling force, E is the elastic modulus, I is the moment of inertia, μ is the calculation length coefficient, and l is the support length. The support prestressing value is determined by active earth pressure calculation: Where P a is the active earth pressure, K a is the active earth pressure coefficient, y is the density of the soil, h is the calculation depth, and c is the cohesion of the soil.

[0203] The specific implementation method of step S20 is to excavate the foundation pit to the designed depth after the construction of the enclosure structure is completed, and to construct reinforced concrete support piles and pile top beams. The purpose of this step is to form a permanent support structure to create conditions for the subsequent construction of the protection plate. The foundation pit is excavated using a layered excavation method, with each layer excavation depth not exceeding 2 meters. The overall stability of the foundation pit is calculated based on the Bishop simplified method: F s =∑[c i b i +(W i -u i b i )tanφ i ]secα i / ∑W i sinα i , where F s is the safety factor, c i is the cohesion of soil, b i is the bar width, W i is the weight of the block, u i is the pore water pressure, φ i is the internal friction angle, α i The supporting piles are bored cast-in-place piles with a pile diameter of 1200 mm. The pile length is determined according to the depth of the bearing layer. The bearing capacity of the bearing layer is calculated by the limit equilibrium formula: Q u =πD∑f i l i +πD 2 q p / 4, where Q u is the ultimate bearing capacity, D is the pile diameter, f i is the pile side resistance, l i is the pile side length, q p The pile end resistance. The concrete strength grade of the pile body is C30, the steel bar is HRB400 grade, and the reinforcement ratio is determined by the limit state design method: ρ = A s / (bh), where ρ is the reinforcement ratio, A s is the steel bar area, b is the cross-section width, and h is the cross-section height. The cross-section size of the pile top beam is 800 mm × 1000 mm, and the moment distribution method is used to calculate the internal force: M ij =2EI(θ i +θ j ) / l, where M ij is the end bending moment, E is the elastic modulus, I is the moment of inertia, θ i ,θ j is the turning angle at both ends, and l is the length of the component.

[0204] The specific implementation method of step S30 is to construct a reinforced concrete protection plate after the support piles and pile top beams are completed, and to construct a reinforced concrete protection structure system of sheet pile structure type. The purpose of this step is to form a protective structure with strong integrity and high rigidity to effectively isolate the upper and lower tunnels. The thickness of the protection plate is 1000 mm, the concrete strength grade is C35, the waterproof grade is P6, and the finite element method is used for structural analysis. The unit division adopts hexahedral twenty-node isoparametric units, and the stress-strain relationship adopts the generalized Hooke's law: {σ}=[D]{ε}, where {σ} is the stress matrix, [D] is the elastic matrix, and {ε} is the strain matrix. The reinforcement design of the plate is based on the ultimate bearing capacity theory, adopts bidirectional reinforcement, and the reinforcement amount is determined by fatigue limit state verification: σ max =σ m +σ a ≤f d , where σ max is the maximum stress, σ m is the mean stress, σ a is the stress amplitude, f d The construction joint is treated with a keyway connection, the keyway depth is 100 mm, the width is 200 mm, and the shear force transmission capacity is calculated by the Mohr Coulomb criterion: τ=c+σ n tanφ, where τ is shear stress, c is cohesion, σ n is the normal stress and φ is the internal friction angle.

[0205] The specific implementation method of step S40 is to use C15 plain concrete to backfill to the designed elevation after the protective structure is completed, and then use 6% cement soil to backfill to the ground in layers. The purpose of this step is to restore the stability of the stratum and create good conditions for shield construction. The plain concrete backfill adopts the pumping method, the mix design is based on the volume method, the water-cement ratio is 0.5, the slump is controlled between 140 mm and 180 mm, and the strength is determined by regression analysis: R c =AR0[1-(W / C-α) 2 ], where R c is the concrete strength, R0 is the cement strength, W / C is the water-cement ratio, and A and α are empirical coefficients. The cement soil backfill adopts the layered compaction method, with each layer thickness of 300 mm and a compaction requirement of not less than 0.94. The compaction is determined by the on-site dry density test: λ=ρ d / ρdma x , where λ is the compaction degree, ρ d is the field dry density, ρdma x is the maximum dry density.

[0206] The specific implementation method of step S50 is to set up a test section within 70 meters before the shield crosses the intersection, and collect soil bin pressure, total thrust, torque, cutter head speed, excavation speed, excavation volume and grouting volume data. The purpose of this step is to obtain the optimal construction parameters through experiments. Parameter collection uses a dynamic monitoring system, and data processing uses a Kalman filter algorithm: X k =AX k-1 +BU k +W k , Z k =HX k +V k , where X k is the state vector, A is the state transfer matrix, U k is the control vector, W k is the process noise, Z k is the observation vector, H is the observation matrix, V k To observe the noise. The soil bin pressure control is based on the earth pressure balance theory: P s =K0γh+q, where P s is the soil bin pressure, K0 is the static soil pressure coefficient, γ is the weight of the soil, h is the burial depth, and q is the surface load. The total thrust is determined by the shield force analysis: F = F c +F f +F p , where F is the total thrust, F c is the cutting resistance, F f is the friction resistance, F p is the positive earth pressure.

[0207] The specific implementation of step S60 is that when the shield tunneling reaches the intersection area, the tunneling speed is controlled to be 5 to 10 mm per minute, and the soil bin pressure is controlled to be 0.6 to 1.0 bar. The purpose of this step is to ensure the stability of the stratum during the shield tunneling process. The tunneling speed control adopts the fuzzy PID control algorithm: u(k) = K p e(k)+K i ∑e(k)+K d [e(k)-e(k-1)], where u(k) is the control quantity, K p , K i , K d are proportional, integral and differential coefficients, and e(k) is the error. The soil bin pressure control adopts a feedforward feedback composite control strategy: P c =P r +AP, where P c To control the pressure, P r is the target pressure, and AP is the pressure correction amount.

[0208] The specific implementation of step S70 is to perform synchronous grouting during shield tunneling, control the grouting pressure at 0.2 to 0.3 MPa, and perform mid-shield grouting within 12.4 meters before and after the intersection. The purpose of this step is to fill the shield construction gap in time and control the deformation of the stratum. The grouting pressure control adopts the proportional integral control algorithm: Where u(t) is the control quantity, K p is the proportionality coefficient, K i is the integral coefficient, and e(t) is the pressure error. Grouting volume calculation is based on the volume compensation principle: Where V g is the grouting volume, D0 is the excavation diameter, D i is the outer diameter of the segment, and L is the excavation length. The middle shield grouting adopts the slurry diffusion theory, and the diffusion radius is calculated by the permeability equation: Where r is the diffusion radius, k is the permeability coefficient, h is the pressure head, t is the grouting time, μ is the slurry viscosity, and n is the soil porosity.

[0209] The specific implementation method of step S80 is that after the shield passes through the intersection, a closed loop is set within 5 meters before and after the intersection, and double-liquid slurry is used for wall grouting, and the grouting pressure is controlled at 0.3 to 0.4 MPa. The purpose of this step is to form an effective water-stop curtain to ensure the waterproof performance of the structure. The double-liquid slurry ratio design is based on the gel time control theory: t g =Ae -B(W / C) , where t g is the gel time, W / C is the water-cement ratio, and A and B are material constants.

[0210] The specific implementation method of step S90 is to use geological radar to scan and detect after the shield has passed for two weeks. The detection frequency is 100 MHz, and the scanning range covers 3 meters of the soil around the tunnel. If a cavity is found, supplementary grouting is immediately carried out, using a double-liquid grouting process, and the grouting pressure is controlled at 0.2 to 0.4 MPa. Keep in touch with the shield machine operating room at any time during supplementary grouting. If abnormal phenomena such as increased soil pressure and increased thrust are found, stop grouting immediately and flush the pipeline. Continue grouting after the abnormal phenomenon is eliminated. After the supplementary grouting is completed, perform a geological radar scan again to confirm the cavity filling effect.

[0211] The following is an example 3 of a specific application scenario of the present invention: This example 3 describes a protective construction method for the intersection construction section of Metro Line 3 and Line 4 in a certain city. The tunnel burial depth of Line 3 is 15.6 meters, the tunnel burial depth of Line 4 is 24.8 meters, and the intersection angle of the two lines is 72 degrees. The strata are mainly the Quaternary Holocene artificial fill layer (Q4ml), the Quaternary Upper Pleistocene alluvial and diluvial layer (Q3al+pl) and the Upper Cretaceous strata (K2). The groundwater is mainly upper stagnant water and bedrock fissure water. This project adopts the open excavation method to implement reinforcement and protection for the intersection section. The specific implementation steps are as follows.

[0212] Construction preparation: First, a comprehensive survey of the construction site was conducted, and 15 surface settlement monitoring points, 5 deep settlement points, and 8 horizontal displacement monitoring points were set up within 30 meters of the intersection area. At the same time, the underground pipeline survey was completed, confirming that there were important pipelines such as DN800 water pipes and DN600 gas pipes in the construction area that needed to be protected. Temporary facilities were set up at the construction site as required, including construction fences, drainage ditches, etc.

[0213] Phase 1: Construction of foundation pit retaining structure

[0214] At the tunnel intersection, an open excavation pit with a length of 32.6 meters, a width of 26.8 meters, and a depth of 28.4 meters was constructed. The foundation pit was protected by φ1200mm bored cast-in-place piles, with a length of 34.5 meters and a spacing of 1.8 meters, for a total of 124 piles. The piles were made of C30 cement concrete and the steel bars were HRB400 grade. Glass fiber bars were used to replace ordinary steel bars in the tunnel passing area. The cross-section size of the crown beam was 1200mm×1000mm, and C30 reinforced concrete was used.

[0215] The foundation pit support system is equipped with four steel supports, using φ609mm (wall thickness 16mm) steel pipes, with a support spacing of 3.0 meters. The first support is set 4.5 meters below the ground, and the second to fourth supports are located at 9.0 meters, 13.5 meters and 18.0 meters respectively. The surrounding purlin is welded with 2 H400×400×13×21 steel sections.

[0216] Analysis of monitoring data of retaining pile construction

[0217] During the construction period, the construction process of the retaining piles was continuously monitored. The maximum horizontal displacement occurred at a depth of 15 meters, with a displacement of 5.8 mm, which was much smaller than the control standard of 20 mm, indicating that the construction quality of the retaining piles was good.

[0218] Phase II: Excavation of foundation pit and construction of support system

[0219] The foundation pit was excavated in layers, with each layer thickness controlled at 2.5 meters. Eight φ1200mm support piles were laid in the foundation pit, with a length of 26.5 meters and a spacing of 3.0 meters. A 800mm×1000mm connecting beam was set on the top of the support pile. The water level of the foundation pit was strictly controlled during the excavation process, and a well point dewatering method was adopted, with a total of 12 dewatering wells laid.

[0220] like Fig.10 As shown in the figure, the surface settlement monitoring data during the foundation pit excavation is provided. This figure shows the relationship between the surface settlement and the water level change during the foundation pit excavation process. From the monitoring data, it can be seen that with the increase of excavation depth, the maximum surface settlement is 9.5 mm and the maximum water level drop is 9.2 meters. The settlement is within the control standard of 30 mm, indicating that the foundation pit support system is in good working condition.

[0221] Phase 3: Protection board construction and backfilling

[0222] The protection plate is made of C30 reinforced concrete with a thickness of 1000mm. The reinforcement is double-layer and bidirectional, with the main reinforcement being φ25@200 and the distribution reinforcement being φ16@200. A 200mm thick C15 plain concrete cushion is set under the plate. The protection plate is cast in blocks, with a total of 4 blocks, each of which is about 8 meters × 13 meters in size.

[0223] Backfilling is divided into two stages: first, C15 plain concrete is used to backfill to the design elevation (elevation -16.5 meters), and after the strength reaches the design requirements, 6% cement soil is used to backfill to the ground in layers. The cement soil backfill is compacted in layers, with each layer thickness controlled at 300mm and a compaction requirement of no less than 94%.

[0224] Phase 4: Shield Construction

[0225] A test section was set up 70 meters before the shield reached the intersection, and the optimal excavation parameters were determined through the test section: soil bin pressure: 0.8 bar; total thrust: 12000 KN; cutterhead speed: 1.2 rpm; excavation speed: 8 mm / min; excavation volume: 4.8 m 3 / ring; grouting volume: synchronous grouting 5.8m 3 / ring, secondary grouting 2.2m 3 / ring.

[0226] Fig.11 This is a data analysis chart of shield tunneling parameter monitoring, showing the changing relationship between soil bin pressure and grouting volume during shield tunneling. At the intersection (distance 0 meters), the soil bin pressure is slightly reduced, and the grouting volume is appropriately increased to ensure the stability of the stratum.

[0227] The following measures were taken when the shield machine passed through the intersection: the excavation speed was slowed down to 5 mm / min; the soil bin pressure was controlled at 0.73-0.78 bar; the synchronous grouting pressure was controlled at 0.25 MPa; the middle shield grouting was carried out within 12.4 meters before and after the intersection, with a grouting pressure of 0.25 MPa; a closed loop was set up within 5 meters before and after the intersection, and double-liquid slurry was used for behind-the-wall grouting, with a grouting pressure of 0.35 MPa.

[0228] Construction effect: By taking the above construction measures, this project has achieved good results:

[0229] 1. The maximum horizontal displacement of the enclosure structure is 5.8 mm, which is less than the control standard of 20 mm.

[0230] 2. The maximum surface settlement during foundation pit excavation was 9.5 mm, which is less than the control standard of 30 mm.

[0231] 3. During the shield tunneling process, the maximum settlement of the existing upper tunnel was 3.2 mm, which is less than the control standard of 10 mm.

[0232] 4. No ground pipeline damage accidents occurred during the construction process.

[0233] 5. Both subway lines were opened to traffic as scheduled.

[0234] This example proves that the sheet pile structure protection system can effectively control the ground deformation and ensure the safety of the cross tunnel construction. Through reasonable construction technology and strict parameter control, the safe crossing of the shield tunnel under complex conditions can be achieved.

[0235] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for protecting the intersecting shield sections, characterized in that: The following steps are involved: S10. Construct an open excavation pit at the tunnel intersection, lay out bored cast-in-place piles and cap beams in the pit as the retaining structure, and set up a steel support system inside the pit; S20. After the construction of the retaining structure is completed, the foundation pit is excavated to the designed depth, and reinforced concrete support piles and pile top beams are constructed; S30, after the supporting piles and pile top beams are completed, a reinforced concrete protection plate is constructed to form a sheet pile structure type reinforced concrete protection structure system; S40. After the protection structure is completed, C15 plain concrete is used to backfill to the designed elevation, and then 6% cement soil is mixed to backfill to the ground in layers; S50. Set up a test section within 70 meters before the shield machine crosses the intersection to collect data on soil bin pressure, total thrust, torque, cutterhead speed, excavation speed, excavation volume and grouting volume; S60: When the shield tunneling reaches the intersection area, the tunneling speed is controlled at 5 to 10 mm / min, and the soil bin pressure is controlled at 0.6 to 1.0 bar; S70: During shield tunneling, synchronous grouting is carried out, with the grouting pressure controlled at 0.2 to 0.3 MPa, and mid-shield grouting is carried out within 12.4 meters before and after the intersection; S80: After the shield passes through the intersection, a closed loop is set up within 5 meters before and after the intersection, and double-liquid slurry is used for wall grouting, and the grouting pressure is controlled at 0.3 to 0.4 MPa; S90. Two weeks after the shield tunnel has passed, geological radar scanning is used to detect voids, and additional grouting is carried out when voids are found.

2. The method for protecting the intersecting shield sections according to claim 1 is characterized in that: The step S10 specifically includes: step 101, surveying the buildings within 30 meters around the foundation pit, setting up monitoring points and collecting initial data; step 102, leveling the site, measuring and positioning the foundation pile position, and positioning by burying the casing, with the top of the casing 0.3 to 0.5 meters above the ground; step 103, using a rotary drill to perform dry hole drilling, first drilling at a low speed to 1 meter below the casing and then adjusting to normal speed; step 104, after drilling, checking the hole depth, hole diameter and verticality to ensure that the pile bottom sediment does not exceed 200 mm; step 105, making a steel cage, dividing it into sections and numbering it according to the designed length, and equipping it with a special bracket during hoisting to ensure that the center line of the steel cage remains consistent when it is docked; step 106, pouring concrete by the catheter method, with the bottom of the catheter 0.3 to 0.5 meters away from the bottom of the hole, and the storage hopper volume meeting the requirements for the depth of the first batch of concrete buried catheters; step 107, checking the concrete surface height and the buried depth of the catheter at any time during pouring, and the buried depth of the catheter is controlled at 2 to 4 meters; Step 108: Use the ring cutting method to cut off the pile head to ensure that the steel bars are not damaged.

3. A method for protecting the intersecting shield sections according to claim 2, characterized in that: The step S20 specifically includes: step 201, excavating the foundation pit by adopting the construction principle of layered excavation and supporting before excavation, and the excavation depth of each layer shall not exceed 0.5 meters below the corresponding support bottom surface; step 202, setting up drainage ditches and water collection wells, the depth of the drainage ditch is 0.4 to 0.5 meters lower than the excavation surface, and is more than 1 meter away from the retaining piles, and the ditch bottom is set with a longitudinal slope of 0.5%; step 203, after the foundation pit is excavated to the designed depth, a bearing capacity test is carried out, and the last 0.3 meters of earthwork is manually excavated; step 204, The support pile positions are staked out and the total station is used for positioning measurement to ensure that the pile position deviation does not exceed 50 mm; step 205, a rotary drilling rig is used to drill the support piles at a drilling speed of 0.5 to 1 meter per minute; step 206, verticality and aperture detection are performed after the hole is cleaned, and the verticality deviation does not exceed 1%; step 207, factory processing of steel cages, on-site hoisting, and positioning blocks are used to control the steel protection layer; step 208, the conduit method is used to pour concrete, and the buried depth of the conduit is not less than 2 meters to ensure the quality of the concrete.

4. A method for protecting the intersecting shield sections according to claim 3, characterized in that: The step S30 specifically includes: step 301, measuring and laying out to determine the position and elevation of the protection plate; step 302, using a combined steel formwork as the protection plate formwork, and the support system uses an adjustable steel pipe support, and the support spacing is not more than 1 meter; step 303, binding the steel bars, the main bars are connected by straight threaded sleeves, the joints are staggered, and the distance between the two joints is not less than 35 times the diameter of the steel bar and not less than 1 meter; step 304, pouring concrete by layered pouring method, the thickness of each layer is controlled at 30 cm, and the vibration is carried out by an inserted vibrator, and the vibration time is 15 to 20 seconds; step 305, the curing period is not less than 7 days, and the temperature difference of the concrete surface is controlled within 20 degrees Celsius during the curing period.

5. A method for protecting the intersecting shield sections according to claim 4, characterized in that: The step S40 specifically includes: step 401, backfilling the foundation pit by layered backfilling and symmetrical tamping; step 402, backfilling the first layer with C15 plain concrete, pumping it into the foundation pit through a concrete pump, and controlling the free fall height to not exceed 2 meters during pouring; step 403, backfilling with cement soil after the plain concrete reaches the design strength, and the virtual thickness of each layer is 250 to 300 mm; step 404, tamping by a combination of mechanical and manual methods, in both vertical and horizontal directions, one tamping and half tamping, and tamping each layer 3 to 4 times; step 405, when backfilling in sections, a 1:2 step is left at the junction, the staggered distance between the upper and lower layers is not less than 1 meter, and the rolling overlap width is 0.5 to 1 meter; step 406, controlling the compaction coefficient of the backfill soil to be not less than 0.94, and performing a density test after each layer of backfilling is completed.

6. A method for protecting the intersecting shield sections according to claim 5, characterized in that: The step S50 specifically includes: step 501, setting a test section within 70 meters before the intersection, controlling the excavation speed to 20 to 30 mm per minute; step 502, controlling the soil bin pressure to 0.15 to 0.2 MPa, and controlling the total thrust to 8000 to 12000 kN; step 503, using a foaming agent to improve the slag, the foam solution is composed of 3% foam additives and 97% water, and the injection amount is 15% to 40% of the excavated earth volume; step 504, controlling the moisture content of the slag to between 30% and 40%, and the water injection amount is 100 to 300 liters per cubic meter; step 505, strictly controlling the tightening torque of the segment assembly bolts, and the segment ovality deviation does not exceed 1% of the design value.

7. A method for protecting the intersecting shield sections according to claim 6, characterized in that: The step S60 specifically includes: step 601, reducing the excavation speed to 5 to 10 mm per minute, and controlling the soil bin pressure at 0.6 to 1.0 bar; step 602, adjusting the pressure of each zone of the propulsion cylinder according to the position of the retaining pile; step 603, strictly controlling the slag discharge volume between 98% and 102% of the theoretical excavation volume; step 604, when cutting piles and excavating, the foam injection volume is 30% of the slag, and the foam pipeline is suspended in stages and in turn; step 605, monitoring the ground settlement data every half an hour, and adjusting the excavation parameters in time according to the monitoring results.

8. The method for protecting the intersecting shield sections according to claim 7 is characterized in that: The step S70 specifically includes: step 701, performing synchronous grouting, and the grouting pressure is controlled at 0.2 to 0.3 MPa; step 702, adopting a dual control standard of pressure and grouting volume, and the grouting volume is determined according to theoretical filling space calculation; step 703, the middle shield grouting adopts bentonite slurry with a consistency of 10 to 20 seconds, and the grouting pressure is also controlled at 0.2 to 0.3 MPa; step 704, performing middle shield grouting within 12.4 meters before and after the intersection to ensure dense filling.

9. A method for protecting the intersecting shield sections according to claim 8, characterized in that: The step S80 specifically includes: step 801, setting a closed loop within 5 meters before and after the intersection, and using double liquid slurry for back-wall grouting; step 802, the double liquid slurry is composed of cement slurry and water glass with a water-cement ratio of 1:1, and a volume ratio of 2:1, and the initial setting time is controlled within 30 seconds; step 803, grouting is carried out from bottom to top, and the grouting pressure is controlled at 0.3 to 0.4 MPa; step 804, secondary grouting is carried out every two rings between the two closed loops, using cement slurry for grouting, and the pressure is also controlled at 0.3 to 0.4 MPa.

10. A method for protecting the intersecting shield sections according to claim 9, characterized in that: The step S90 specifically includes: step 901, after the shield machine has passed for two weeks, use geological radar to scan and detect, the detection frequency is 100 MHz, and the scanning range covers 3 meters of the soil around the tunnel; step 902, if a cavity is found, immediately carry out supplementary grouting, use a double-liquid grouting process, and control the grouting pressure at 0.2 to 0.4 MPa; step 903, keep in touch with the shield machine operating room at any time during supplementary grouting, if abnormal phenomena such as increased soil pressure and increased thrust are found, immediately stop grouting and flush the pipeline; step 904, continue grouting after the abnormal phenomenon is eliminated; step 905, after the supplementary grouting is completed, perform geological radar scanning again to confirm the cavity filling effect.

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