Foundation structure underpinning construction method for shield tunnel to penetrate through upper building pile foundation

Abstract

The invention discloses a foundation structure underpinning construction method for a shield tunnel to penetrate through an upper building pile foundation, and belongs to the technical field of tunnel engineering pile foundation underpinning. The method comprises the following steps that grouting reinforcement is conducted on a foundation below a building foundation in a tunnel underpass area, and a tracking grouting condition is reserved on the edge of an original bearing platform; shallow foundation pit excavation is adopted, and a beam plate type raft foundation is constructed; steel supports are additionally arranged around first-layer columns of the building to serve as temporary supports; shield tunneling construction is carried out; and tracking grouting is conducted according to the monitoring result, and finally the foundation pit is backfilled. The problems that when a traditional shield tunnel penetrates through a building under the ground, the tunnel burial depth is changed or a house is directly dismantled, so that additional cost is increased, and the construction period is delayed are solved; the influence of pile grinding of the shield tunneling machine on a building above can be reduced; and house demolition is not needed, only shallow foundation pit operation is carried out, the safety of a tunnel lining structure and an upper building is protected, and construction continuity is guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel engineering pile foundation underpinning, and in particular relates to a foundation structure underpinning construction method for a shield tunnel passing through an upper building pile foundation. Background Art

[0002] In urban subway construction projects, due to the constraints of the geographical environment, tunnel lines often conflict with buildings or bridge pile foundations. When tunnel construction passes through pile foundations, it will inevitably damage their upper structures, causing surface settlement and even tilting and cracking of buildings or bridge abutments. One of the traditional solutions is to change the line to bypass buildings or increase the depth of tunnels and stations in the early planning stage of the project to avoid their influence, but this will increase the difficulty of construction and bring inconvenience to passengers. Another solution is to demolish the house before shield construction, and remove the residual pile foundation from the ground by pulling out or flushing the piles, and then grouting backfill after pulling out the piles.

[0003] The cost of house demolition and expropriation by the pile extraction method is high, and it has a great impact on the surrounding environment, especially in densely populated and busy traffic areas in the city center. On the other hand, the full-rotation drilling rig pile extraction method has high equipment prices and low construction efficiency when extracting prefabricated square piles, pipe-sinking cast-in-place piles, and prestressed pipe piles. Although the flushing pile extraction method has low construction costs and high efficiency, due to a large amount of mud pollution, the old pile position has become muddy, and the old pile hole cannot be densely backfilled. It may also cause water and mud gushing, ground collapse, and settlement and cracking of surrounding buildings in areas where the groundwater level is 1 to 2 meters below the surface. The high-pressure rotary jet mud pile extraction method is prone to broken piles, is greatly affected by the density of the stratum soil, and has a large stratum disturbance, so it is not suitable for the extraction of prefabricated piles.

[0004] Therefore, there is an urgent need for a construction method that does not require changing the tunnel route and burial depth, avoids demolishing houses and pile foundations, saves construction costs, and has less impact on the environment. Summary of the invention

[0005] The purpose of an embodiment of the present invention is to provide a method for replacing the foundation structure of a shield tunnel passing through the pile foundation of an upper building. The method reinforces the foundation below the house foundation by grouting, and adopts shallow foundation pit excavation to construct a beam-slab raft foundation to disperse the load transferred to the original pile foundation to reduce the impact of the shield machine grinding piles on the stratum and the house. The original pile foundation and pedestal and the newly built raft foundation and foundation beam can form a replacement system together, thereby reducing the requirements for the construction site, reducing the construction difficulty and cost, and reducing the impact on the environment, thereby solving at least one technical problem involved in the background technology.

[0006] In order to solve the above-mentioned technical problems, the present invention is achieved as follows:

[0007] An embodiment of the present invention provides a foundation structure underpinning construction method for a shield tunnel passing through a pile foundation of an upper building, comprising the following steps:

[0008] Step S1, grouting reinforcement is performed on the foundation below the building foundation in the tunnel underpass area, and tracking grouting conditions are reserved at the edge of the original cap;

[0009] Step S2, excavating a shallow foundation pit and constructing a beam-slab raft foundation;

[0010] Step S3, adding steel supports around the columns of the first floor of the building as temporary supports;

[0011] Step S4, performing shield tunneling construction;

[0012] Step S5, perform tracking grouting according to the monitoring results, and finally backfill the foundation pit.

[0013] Optionally, in step S1, before grouting reinforcement is performed on the foundation below the building foundation in the tunnel underpass area, the method further includes:

[0014] Check all pipelines on site, measure and mark out, confirm the plane position of the building foundation, and demolish the side columns and corner column walls according to the plane position of the building foundation. When demolishing, pay attention to reserving an operating space of no less than 50 cm on both sides of the building foundation.

[0015] Optionally, in step S1, the grouting range is: 3m outward from the building foundation plane, and 6m vertically from the bottom of the pedestal to the bottom;

[0016] Grouting parameters: Φ48 sleeve raft tube grouting is used, the spacing between grouting holes is 1.5m×1.5m, and the plum blossom type arrangement is adopted; cement slurry is used for grouting, the water-cement ratio of slurry is recommended to be 1.5-1.1, the grouting pressure is 0.5-1.0MPa, the grouting pressure is gradually increased, and it is stable for 10 minutes after reaching the grouting pressure; the slurry diffusion radius is not less than 0.7m;

[0017] Grouting method: When grouting multiple rows of holes, the interval grouting is adopted first from the outside and then from the inside. The interval grouting of the same row of holes is skipped, and the interval grouting time is greater than 3 hours. For soil layers with groundwater flow, grouting is started from the end with high water head. For soil layers with similar permeability coefficients, grouting is performed from the top first and then from the bottom to the top. For strata whose permeability coefficient increases with depth, grouting is performed from the bottom to the top. When the soil properties of the strata vary greatly and the permeability coefficients differ greatly, mixed segmented grouting is adopted to strengthen grouting at the interface of the soil layers.

[0018] The grouting end standard is: the final pressure value of the designed grouting pressure is taken as the hydrostatic pressure at the grouting location + 0.5MPa. When the single hole grouting pressure reaches the designed final pressure value and the grouting continues for 10 minutes, the grouting of this hole is ended; the grouting volume of a single hole is roughly the same as the designed grouting volume, and the grouting volume at the end is 20-30L / min, and the grouting of this hole is ended;

[0019] Grouting result inspection: Grouting inspection should be carried out 28 days after the completion of grouting; the number of grouting inspection points should not be less than 2% to 5% of the number of grouting holes. When the inspection pass rate is less than 80%, repeated grouting should be carried out on the unqualified grouting areas; after all grouting holes are grouted, drill at least 3 holes for inspection, and take core samples to observe the slurry filling situation. At the same time, check that the water inflow in the hole should not be greater than 0.2L / min·m, and the water leakage at a certain point should not be greater than 10L / min; or conduct a water pressure test, and check that the water inflow in the hole should be less than 10L / min·m under a pressure of 1.0MPa; after grouting, the soil should have good uniformity and self-sustaining properties, and there should be no obvious water seepage on the face of the tunnel, and the permeability coefficient should be less than 1.0×10 -6 cm / s, the unconfined compressive strength shall not be less than 1.0MPa, otherwise, the drilling holes shall be increased and grouting shall be continued.

[0020] Optionally, in step S1, after grouting reinforcement is performed on the foundation below the building foundation in the tunnel underpass area, the method further includes:

[0021] Test of foundation bearing capacity and deformation modulus: After the foundation reinforcement under the building is completed, a static load test should be carried out. The number of tests for each single building should be no less than 3 points. The foundation bearing capacity shall not be less than 140kPa; the deformation modulus shall not be less than 80MPa.

[0022] Optionally, in step S2, a shallow foundation pit is excavated to construct a beam-slab raft foundation, which specifically includes:

[0023] When the excavation depth of the foundation pit is lower than the groundwater level and soil flow may occur in the soil layer, reliable water reduction (interception) measures should be taken to lower the groundwater level before excavating the foundation pit; when the soil quality is good, open ditches and water collection wells can be used for drainage; the ground drainage ditches around the foundation pit should be kept unobstructed without water leakage or seepage; strictly prevent the water discharged from the foundation pit and the rainwater on the ground from flowing back into the foundation pit;

[0024] During the foundation pit construction process, the designed slope should be adjusted in time according to the excavation situation, and attention should be paid to whether there are original weak structural surfaces in the soil. If necessary, soil nails and other measures can be used for reinforcement, and monitoring should be strengthened;

[0025] From the start of foundation pit excavation to the completion of foundation pit backfilling, the additional pit load shall not exceed the design value;

[0026] From the beginning of foundation pit excavation to the completion of foundation pit backfilling, the pit top displacement should be monitored and records should be kept; after the foundation pit construction is completed, the foundation pit depth, slope, slope protection and drainage system should be comprehensively inspected and recorded.

[0027] Optionally, in step S3, steel supports are added around the columns of the first floor of the building as temporary supports, specifically including:

[0028] After the raft foundation construction is completed and reaches a certain strength, steel supports are erected, with one end supported on the raft foundation and the other end supported at the intersection of the crisscross beams; the steel supports are pre-assembled on the ground, and steel supports of appropriate length are selected for assembly based on the clearance. Forklifts are used for installation, and excavators are used to assist in the construction. After the installation is completed, a certain force is applied to ensure that there is no air between the steel supports and the beams.

[0029] Optionally, in step S4, shield tunneling construction is performed, specifically including:

[0030] After the shield machine cut through the piles, zoning management of crossing excavation was implemented for the crossing project. The 9m before and after the building under the danger zone is the danger zone, and the 9m range outside the danger zone is the risk zone. In the risk zone, combined with the results of stratum deformation monitoring, we continue to optimize and improve various control technical parameters, implement personnel job responsibilities, and reserve materials and supplies to lay a good foundation for the formal crossing; in terms of excavation management, in the crossing area, full-storage excavation is achieved, and the amount of excavated is strictly controlled; after the left and right lines of the shield section have successfully completed the excavation of the two risk zones before and after the building and the three sections of the danger zone, the construction of the pile grinding building under this section has been successfully completed.

[0031] Optionally, in step S5, tracking grouting is performed according to the monitoring results, and finally the foundation pit is backfilled, which specifically includes:

[0032] When the shield passes through, pay attention to controlling the shield excavation parameters, timely synchronous grouting, timely secondary grouting, and increase the grouting volume to minimize the disturbance of the stratum due to over-excavation and control the deformation of the stratum; after the shield passes through the building, continue to monitor and measure the structure of the building after excavation, and conduct 24-hour inspections. Once it is found that the deformation of the building reaches the alarm value, take ground sleeve raft tube tracking grouting reinforcement measures in a timely manner in an emergency; after the monitoring data is confirmed, backfill the foundation pit.

[0033] Optionally, in step S5, the foundation pit backfill material may be any fresh soil except silt, silt sand, miscellaneous soil, humus soil with an organic content greater than 8%, over-wet soil, frozen soil, and stones with a particle size greater than 150 mm.

[0034] Optionally, in step S5, the accumulated water and debris in the pit should be cleaned up before backfilling, the loose soil that is suitable for backfilling should be compacted, and backfilling can only be carried out after passing the hidden inspection. The foundation pit backfill should be layered and compacted horizontally, with each layer being 200 to 300 mm thick; during backfilling, machinery or equipment must not collide with the reinforcement base; machinery and equipment should be used to tamp the structure on both sides and within 500 mm of the top plate and around underground pipelines.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The present invention solves the problem of additional cost and construction delay caused by changing the tunnel burial depth or directly demolishing the building when the traditional shield tunnel passes under the building;

[0037] 2. The present invention first performs grouting reinforcement on the foundation below the house foundation in the tunnel underpass area, and reserves tracking grouting conditions at the edge of the original cap, and then uses shallow foundation pit excavation to construct the beam-slab raft foundation and adds steel supports around the columns of the first floor of the house as temporary supports. The load borne by the original pile foundation is transferred to the soil layer below through the cap and the raft foundation, thereby reducing the impact of the shield machine grinding pile on the upper building;

[0038] 3. The method provided by the present invention does not require house demolition and only requires shallow foundation pit operations, thereby protecting the safety of the tunnel lining structure and upper buildings and ensuring the continuity of construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work, among which:

[0040] Figure 1 It is a flow chart of a foundation structure underpinning construction method for a shield tunnel passing through a pile foundation of an upper building provided by the present invention;

[0041] Figure 2 It is one of the construction structure schematic diagrams provided by the present invention;

[0042] Figure 3 This is the second schematic diagram of the construction structure provided by the present invention;

[0043] Figure 4 This is the third schematic diagram of the construction structure provided by the present invention;

[0044] Figure 5 It is a construction site map provided by the present invention. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] The terms "first", "second", etc. in the specification and claims of the present invention are used to distinguish similar objects, and are not used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention can be implemented in an order other than those illustrated or described herein, and the objects distinguished by "first", "second", etc. are generally of the same type, and the number of objects is not limited. For example, the first object can be one or more. In addition, "and / or" in the specification and claims represents at least one of the connected objects, and the character " / " generally indicates that the objects associated with each other are in an "or" relationship.

[0047] In conjunction with the accompanying drawings, the foundation structure underpinning construction method for a shield tunnel passing through a pile foundation of an upper building provided by an embodiment of the present invention is described in detail through specific embodiments and application scenarios.

[0048] See also Figure 1 As shown, an embodiment of the present invention provides a foundation structure underpinning construction method for a shield tunnel passing through a pile foundation of an upper building, comprising the following steps:

[0049] Step S1, grouting reinforcement is performed on the foundation below the building foundation in the tunnel underpass area, and tracking grouting conditions are reserved at the edge of the original cap;

[0050] Step S2, excavating a shallow foundation pit and constructing a beam-slab raft foundation;

[0051] Step S3, adding steel supports around the columns of the first floor of the building as temporary supports;

[0052] Step S4, performing shield tunneling construction;

[0053] Step S5, perform tracking grouting according to the monitoring results, and finally backfill the foundation pit.

[0054] In step S1, a SD map is obtained from OpenStreetMap.

[0055] The following is a detailed description of the foundation structure underpinning construction method for a shield tunnel passing through a pile foundation of an upper building provided by the present invention with reference to a specific embodiment.

[0056] Project Introduction

[0057] Shenzhen-Huizhou Intercity Railway Dapeng Branch Line Longping Section Underpass Yongyuanjin Industrial Park Project, such as Figure 2As shown, the tunnel passes under the planned houses to be demolished at mileages ZDK9+500~ZDK9+552, YDK9+535~YDK9+582, including Building 1 and Building 4 of Yongyuanjin Industrial Park. The foundations of the houses to be demolished are φ0.4m prestressed pipe piles with a depth of 12.3m~21.3m. The tunnel is buried at a depth of about 13.7-14.5m. 58 pile foundations invade the tunnel of this line (54 pile foundations invade the Shenzhen-Dalian intercity tunnel), totaling 112 piles.

[0058] Construction process

[0059] Combination Figures 2 to 5 As shown, this embodiment provides a foundation structure underpinning construction method for a shield tunnel passing through a pile foundation of an upper building, specifically comprising:

[0060] Step S1: Remove the bottom slabs / side walls of buildings 1 and 4 through which tunnel 1 passes, perform grouting reinforcement on the foundation below the building foundation, and reserve tracking grouting conditions at the edge of the original foundation;

[0061] First, check all pipelines on site, measure and lay out, confirm the foundation plane position, and break down the side columns and corner column walls according to the foundation plane position. When breaking down, pay attention to reserving an operating space of no less than 50 cm on both sides of the foundation; use a jackhammer to break down the original ground floor.

[0062] Grouting range: 3m outside the house plane (i.e. beam-slab raft foundation range), vertically from the bottom of the pedestal to 6m below (including the fill layer and silty clay layer), such as Figure 3 shown.

[0063] Grouting parameters: In the grouting reinforcement area 5, Φ48 sleeve raft tube 4 is used for grouting, the spacing between grouting holes is 1.5m×1.5m, and they are arranged in plum blossom shape; cement slurry is used for grouting, the water-cement ratio of the slurry is recommended to be 1.5~1.1, the grouting pressure is 0.5~1.0MPa, the grouting pressure is gradually increased, and it is stable for 10 minutes after reaching the grouting pressure; the slurry diffusion radius is not less than 0.7m; the above parameters are for experimental reference only and shall be determined based on on-site experiments.

[0064] Grouting method: When grouting multiple rows of holes, adopt interval grouting from the outside to the inside. For the same row of holes, perform interval grouting in a jump-type manner, and the interval grouting time is greater than 3 hours. For soil layers with groundwater flow, start grouting from the end with high water head. For soil layers with similar permeability coefficients, grouting is performed to seal the top and then grouting is performed from bottom to top. For strata whose permeability coefficient increases with depth, grouting is performed from bottom to top. When the soil properties of the strata vary greatly and the permeability coefficients differ greatly, mixed segmented grouting should be used to strengthen grouting at the soil layer interface.

[0065] End standard of grouting: The designed grouting pressure (final pressure value) is generally taken as the hydrostatic pressure at the grouting point + 0.5MPa. When the grouting pressure of a single hole reaches the designed final pressure and grouting continues for 10 minutes, the grouting of this hole can be ended. The grouting volume of a single hole is roughly the same as the designed grouting volume. When the grouting volume at the end is below 20-30L / min, the grouting of this hole can be ended.

[0066] Inspection of grouting results: Grouting inspection should be carried out 28 days after the completion of grouting; the number of grouting inspection points should not be less than 2% to 5% of the number of grouting holes. When the inspection pass rate is less than 80%, repeated grouting should be carried out on the unqualified grouting areas. After all the grouting holes are filled, drill at least 3 holes for inspection, and take core samples to observe the slurry filling conditions. At the same time, check that the water inflow in the hole should not be greater than 0.2L / min·m, and the water leakage at a certain point should not be greater than 10L / min; or conduct a water pressure test, and check that the water inflow in the hole should be less than 10L / min·m under a pressure of 1.0MPa. After grouting, the soil should have good uniformity and self-sustaining properties, there should be no obvious water seepage on the face, and the permeability coefficient should be less than 1.0×10 -6 cm / s, the unconfined compressive strength shall not be less than 1.0MPa, otherwise, the drilling holes shall be increased and grouting shall be continued.

[0067] Test of foundation bearing capacity and deformation modulus: After the foundation reinforcement under the house is completed, a static load test should be carried out. The number of tests for each single building should be no less than 3 points. The foundation bearing capacity shall not be less than 140kPa; the deformation modulus shall be no less than 80MPa.

[0068] Step S2: excavating a shallow foundation pit and constructing a beam-slab raft foundation;

[0069] A shallow foundation pit is excavated under Buildings 1 and 4 of Yongyuanjin Industrial Park. A 60-type small excavator is used to excavate the foundation pit. The size of the foundation pit is larger than the layout size, with an operating space of no less than 50cm on each side. The excavation depth is 2.5m, the slope is 1.0, and 10 600×600×600mm water collection wells are set around the pit. A 0.2m high and 0.2m wide water retaining sill is set on the top of the pit, and a 0.2m high and 0.2m wide drainage ditch is set at the bottom of the pit. The slope surface is sprayed with 100mm thick C20 concrete, and a single-layer steel mesh φ8@150mm is hung.

[0070] When the excavation depth of the foundation pit is lower than the groundwater level and soil flow may occur in the soil layer, reliable water reduction (interception) measures should be taken to lower the groundwater level before excavating the foundation pit; when the soil quality is good, open ditches and water collection wells can be used for drainage. The ground drainage ditches around the foundation pit should be kept unobstructed without water leakage or seepage; strictly prevent the water discharged from the foundation pit and the rainwater on the ground from flowing back into the foundation pit.

[0071] During the foundation pit construction process, the designed slope should be adjusted in time according to the excavation situation, and attention should be paid to whether there are native weak structural surfaces in the soil. If necessary, soil nails and other measures can be used for reinforcement, and monitoring should be strengthened.

[0072] From the beginning of foundation pit excavation to the completion of foundation pit backfilling, the additional load on the pit shall not exceed the design value.

[0073] From the beginning of foundation pit excavation to the completion of foundation pit backfilling, the pit top displacement should be monitored and records should be kept; after the foundation pit construction is completed, the foundation pit depth, slope, slope protection and drainage system should be comprehensively inspected and recorded.

[0074] Construct a beam-slab raft foundation with a thickness of 0.5m raft slab (the range is 3m outside the existing house) + a 2.0m×1.0m wide and high ground beam, connect the cap as a whole, the bottom of the beam is flush with the bottom of the raft slab, turn up 500mm foundation beam 7 and connect it with the existing cap 2 reinforcement, and roughen the cap surface; lay a 150mm thick C20 plain concrete cushion under the foundation, such as Figure 4 shown.

[0075] The concrete grade of raft foundation 6 is C35, the steel grade is CHRB400, BHPB300, the main reinforcement of the raft is arranged in two-way double layers, the plate surface reinforcement and surface reinforcement are C20@100, reinforcing ribs are set locally on the raft, and the thickness of the steel bar protective layer is 40mm.

[0076] Before pouring the raft foundation beam 7, the surface of the existing pedestal 2 of the house should be cleaned in time. When pouring the raft foundation beam 7, the concrete pouring surface should be appropriately higher than the surface of the existing pedestal 2 and be vibrated and compacted. There should be no gaps on the contact surface with the bottom of the pedestal. If there is a gap between the foundation beam 7 and the ground of the existing pedestal 2 due to concrete shrinkage, cement slurry should be used to fill it tightly.

[0077] At the junction of the new and old concrete of the pile foundation and the raft foundation 6, the surface of the original concrete should be roughened and rinsed clean according to the reinforcement specifications, and the original concrete should be fully moistened and brushed with interface bonding agent before pouring concrete.

[0078] Step S3: Temporary steel support measures are added around the columns of the first floor of the building;

[0079] Since houses 1 and 4 involve a large number of pile foundations 3, steel supports 9 are required to provide temporary support around the columns 8. After the raft foundation construction is completed and reaches a certain strength, the steel supports 9 are erected. The diameter of the steel support 9 is 609mm. One section is supported on the raft foundation, and the other section is supported at the intersection of the cross beams. Figure 5 shown.

[0080] The steel supports 9 are pre-assembled on the ground. Steel supports 9 of appropriate length are selected according to the clearance for assembly. A 5-ton forklift is used for installation, and a 60-ton excavator is used for auxiliary construction. After the installation is completed, a certain force is applied to ensure that there is no air between the steel supports 9 and the beam.

[0081] Step S4: After the construction is completed, shield tunneling construction is carried out;

[0082] After the shield machine cuts the piles, the crossing project is managed by zoning. The 9m before and after the building is a dangerous area, and the 9m outside the dangerous area is a risk area. In the risk area, we will continue to optimize and improve various control technical parameters, such as shield excavation parameters, slag improvement foam parameters and grouting ratio parameters, mainly based on the results of stratum deformation monitoring, to implement personnel job responsibilities, materials and supplies reserves, and lay a good foundation for the formal crossing; in terms of excavation management, in the crossing area, we will try to achieve full excavation and more strictly control the amount of excavated materials.

[0083] After the left and right lines of the shield section of this project successfully completed the excavation of three sections of the two risk areas and the dangerous area before and after the building, it was declared that the construction of the underpass of the pile grinding building in this section was successfully completed.

[0084] Step S5: Carry out tracking grouting according to the monitoring results, and finally backfill the foundation pit.

[0085] When the shield passes through, pay attention to controlling the shield excavation parameters, timely synchronous grouting, timely secondary grouting, and increasing the grouting volume to minimize the disturbance of the stratum caused by over-excavation and control the deformation of the stratum.

[0086] After the shield passes through the building, it continues to monitor and measure the building structure after excavation, and conducts 24-hour inspections. Once it is found that the deformation of the building reaches the alarm value, ground sleeve raft tube tracking grouting reinforcement measures are taken in a timely manner in an emergency situation.

[0087] After the monitoring data is confirmed, the foundation pit will be backfilled and the houses, roads, pipelines, etc. within the site will be restored to their original state.

[0088] Except for silt, silt sand, miscellaneous soil, humus soil with an organic content greater than 8%, over-wet soil, frozen soil and stones with a particle size greater than 150mm, all other fresh soil can be backfilled into the foundation pit.

[0089] Before backfilling, the water and debris in the pit should be cleaned up, the loose soil that meets the requirements of backfilling should be compacted, and backfilling can be carried out only after passing the hidden inspection. The backfill of the foundation pit should be layered and compacted horizontally, with a thickness of 200 to 300 mm for each layer; during backfilling, machinery or equipment should not collide with the reinforcement cap. The two sides of the structure and the top plate within 500 mm, as well as around the underground pipelines, should be compacted manually using small equipment.

[0090] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0091] In addition, it should be noted that the scope of the methods and devices in the embodiments of the present invention is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in reverse order according to the functions involved. For example, the described methods may be performed in an order different from that described, and various steps may be added, omitted, or combined. In addition, features described with reference to certain examples may be combined in other examples.

[0092] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A method for replacing the foundation structure of a shield tunnel passing through a pile foundation of an upper building, characterized in that: The following steps are involved: Step S1, grouting reinforcement is performed on the foundation below the building foundation in the tunnel underpass area, and tracking grouting conditions are reserved at the edge of the original cap; Step S2, excavating a shallow foundation pit and constructing a beam-slab raft foundation; Step S3, adding steel supports around the columns of the first floor of the building as temporary supports; Step S4, performing shield tunneling construction; Step S5, perform tracking grouting according to the monitoring results, and finally backfill the foundation pit.

2. The method according to claim 1, characterized in that In step S1, before grouting reinforcement is performed on the foundation below the building foundation in the tunnel underpass area, the following steps are also included: Check all pipelines on site, measure and mark out, confirm the plane position of the building foundation, and demolish the side columns and corner column walls according to the plane position of the building foundation. When demolishing, pay attention to reserving an operating space of no less than 50 cm on both sides of the building foundation.

3. The method according to claim 2, characterized in that In step S1, the grouting range is: 3m outward from the building foundation plane, and 6m vertically from the bottom of the pedestal to the bottom; Grouting parameters: Φ48 sleeve raft tube grouting is used, the spacing between grouting holes is 1.5m×1.5m, and the plum blossom type arrangement is adopted; cement slurry is used for grouting, the water-cement ratio of slurry is recommended to be 1.5-1.1, the grouting pressure is 0.5-1.0MPa, the grouting pressure is gradually increased, and it is stable for 10 minutes after reaching the grouting pressure; the slurry diffusion radius is not less than 0.7m; Grouting method: When grouting multiple rows of holes, the interval grouting is adopted first from the outside and then from the inside. The interval grouting of the same row of holes is skipped, and the interval grouting time is greater than 3 hours. For soil layers with groundwater flow, grouting is started from the end with high water head. For soil layers with similar permeability coefficients, grouting is performed from the top first and then from the bottom to the top. For strata whose permeability coefficient increases with depth, grouting is performed from the bottom to the top. When the soil properties of the strata vary greatly and the permeability coefficients differ greatly, mixed segmented grouting is adopted to strengthen grouting at the soil layer interface. Grouting end standard: the final pressure value of the designed grouting pressure is taken as the hydrostatic pressure at the grouting location + 0.5MPa. When the single-hole grouting pressure reaches the designed final pressure value and the grouting continues for 10 minutes, the grouting of this hole is ended; the grouting volume of a single hole is roughly the same as the designed grouting volume, and the grouting volume at the end is 20-30L / min, and the grouting of this hole is ended; Grouting result inspection: Grouting inspection should be carried out 28 days after the completion of grouting; The number of grouting inspection points should not be less than 2% to 5% of the number of grouting holes. When the inspection pass rate is less than 80%, repeated grouting should be carried out on the unqualified grouting areas. After all the grouting holes are grouted, at least 3 holes should be drilled for inspection, and core samples should be taken to observe the grouting filling situation. At the same time, the water inflow in the hole should not be greater than 0.2L / min·m, and the water leakage at a certain point should not be greater than 10L / min; or a water pressure test should be carried out to check that the water inflow in the hole should be less than 10L / min·m under a pressure of 1.0MPa. After grouting, the soil should have good uniformity and self-sustaining properties, and there should be no obvious water seepage on the face. The permeability coefficient should be less than 1.0×10 -6 cm / s, the unconfined compressive strength shall not be less than 1.0MPa, otherwise, the drilling holes shall be increased and grouting shall be continued.

4. The method according to claim 3, characterized in that In step S1, after grouting reinforcement is performed on the foundation below the building foundation in the tunnel underpass area, the following steps are also included: Test of foundation bearing capacity and deformation modulus: After the foundation reinforcement under the building is completed, a static load test should be carried out. The number of tests for each single building should be no less than 3 points. The foundation bearing capacity shall not be less than 140kPa; the deformation modulus shall not be less than 80MPa.

5. The method according to claim 2, characterized in that: In step S2, a shallow foundation pit is excavated to construct a beam-slab raft foundation, which specifically includes: When the excavation depth of the foundation pit is lower than the groundwater level and soil flow may occur in the soil layer, take precipitation measures to lower the groundwater level before excavating the foundation pit; when the soil quality is good, use open ditches and water collection wells for drainage; the ground drainage ditches around the foundation pit should be kept unobstructed without water leakage or seepage; strictly prevent the water discharged from the foundation pit and the rainwater on the ground from flowing back into the foundation pit; During the foundation pit construction process, the design slope should be adjusted in time according to the excavation situation, and attention should be paid to whether there are original weak structural surfaces in the soil. If necessary, soil nailing measures should be used for reinforcement, and monitoring should be strengthened; From the start of foundation pit excavation to the completion of foundation pit backfilling, the additional pit load shall not exceed the design value; From the beginning of foundation pit excavation to the completion of foundation pit backfilling, the pit top displacement should be monitored and records should be kept; after the foundation pit construction is completed, the foundation pit depth, slope, slope protection and drainage system should be comprehensively inspected and recorded.

6. The method according to claim 1, characterized in that In step S3, steel supports are added around the columns of the first floor of the building as temporary supports, which specifically includes: After the raft foundation construction is completed and reaches a certain strength, steel supports are erected, with one end supported on the raft foundation and the other end supported at the intersection of the crisscross beams; the steel supports are pre-assembled on the ground, and steel supports of appropriate length are selected for assembly based on the clearance. Forklifts are used for installation, and excavators are used to assist in the construction. After the installation is completed, a certain force is applied to ensure that there is no air between the steel supports and the beams.

7. The method according to claim 1, characterized in that In step S4, shield tunneling construction is carried out, which specifically includes: After the shield machine cut through the piles, zoning management of crossing excavation was implemented for the crossing project. The 9m before and after the building under the danger zone is the danger zone, and the 9m range outside the danger zone is the risk zone. In the risk zone, combined with the results of stratum deformation monitoring, we continue to optimize and improve various control technical parameters, implement personnel job responsibilities, and reserve materials and supplies to lay a good foundation for the formal crossing; in terms of excavation management, in the crossing area, full-storage excavation is achieved, and the amount of excavated is strictly controlled; after the left and right lines of the shield section have successfully completed the excavation of the two risk zones before and after the building and the three sections of the danger zone, the construction of the pile grinding building under this section has been successfully completed.

8. The method according to claim 1, characterized in that: In step S5, tracking grouting is performed according to the monitoring results, and finally the foundation pit is backfilled, which specifically includes: When the shield passes through, pay attention to controlling the shield excavation parameters, timely synchronous grouting, timely secondary grouting, and increase the grouting volume to minimize the disturbance of the stratum due to over-excavation and control the deformation of the stratum; after the shield passes through the building, continue to monitor and measure the structure of the building after excavation, and conduct 24-hour inspections. Once it is found that the deformation of the building reaches the alarm value, take ground sleeve raft tube tracking grouting reinforcement measures in a timely manner in an emergency; after the monitoring data is confirmed, backfill the foundation pit.

9. The method according to claim 8, characterized in that In step S5, the foundation pit backfill material can be backfilled with fresh soil except silt, silt sand, miscellaneous soil, humus soil with an organic content greater than 8%, over-wet soil, frozen soil and stones with a particle size greater than 150 mm.

10. The method according to claim 9, characterized in that In step S5, the accumulated water and debris in the pit should be cleaned before backfilling, the loose soil that is suitable for backfilling should be compacted, and backfilling can only be carried out after passing the hidden inspection. The foundation pit backfill should be layered and compacted horizontally, with a thickness of 200 to 300 mm for each layer; during backfilling, machinery or equipment must not collide with the reinforcement foundation; both sides of the structure and within 500 mm of the top plate and around the underground pipelines should be tamped with equipment.

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