Hopper-shaped subsidence area foundation pit composite cofferdam leakage water plugging construction method

Abstract

The invention discloses a construction method for leaking water leakage stoppage of a funnel-shaped subsidence area foundation pit composite cofferdam. The construction method comprises the following steps that materials are prepared and inspected; breaking before construction: breaking the existing cement mixing piles and the existing concrete ground and the existing concrete drainage ditches at the top of the subsidence area; steel sheet piles are inserted and driven downwards in the subsidence area and the non-subsidence area outside the subsidence area, so that the subsidence area is divided into an inner leaking stoppage treatment area and an outer leaking stoppage treatment area which are sequentially arranged front and back, and the two transverse sides of the steel sheet piles are connected with the existing cement mixing piles in a sealed mode correspondingly; leaking stoppage filling construction is conducted, specifically, the inner closed filling area and the outer leaking stoppage treatment area are filled with filling materials prepared from filling materials; and repouring after filling: repouring concrete at the filler, the soil layer outside the foundation pit and the top end of the existing cement mixing pile to form a concrete ground and a concrete drainage ditch. According to the construction method, the problems existing in an existing method are effectively solved, the leaking stoppage construction technology is easy and convenient to operate, the construction cost is low, and wide application and popularization are facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of water seepage plugging of foundation pit cofferdams, and in particular to a construction method for water seepage plugging of a composite cofferdam of a foundation pit in a funnel-shaped subsidence area. Background Art

[0002] In a bridge project in the Guangdong Delta Plain, the bridge 7# main pier cap passes through the clay layer, silty clay layer, medium sand layer, silty silt sand layer, silty silty clay layer, and is located on the silty silty clay layer. During the cap construction, the steel sheet piles were inserted into the silty silty clay layer with a burial depth of 18m, so that the top of the steel sheet pile was 0.5m higher than the top surface of the soil layer outside the foundation pit, and a row of cement mixing piles with a width of 0.60m and a pile length of 8.0m were constructed on the outside of the steel sheet piles, so that the top of the cement mixing piles was flush with the surface of the soil layer outside the foundation pit and abutted against the outside of the steel sheet piles, and a 0.20m thick concrete floor and a concrete drainage ditch on it were poured at the top of the cement mixing piles and the top of the soil layer outside the foundation pit to form a composite cofferdam for the cap foundation pit. However, due to the encounter of isolated rocks during the driving of steel sheet piles, the "S" shape of the steel sheet pile cofferdam after the driving construction, or the serious deformation of the lock of the steel sheet pile due to repeated use, the lock of the steel sheet pile may not fit or may be disengaged, and the cement mixing piles may not fit tightly together and gaps may appear between the piles, forming leakage points. As a result, the groundwater outside the cofferdam of the pedestal foundation pit infiltrates into the pedestal foundation pit through the leakage points, causing water accumulation in the foundation pit, affecting the construction of the pedestal foundation pit, or the construction sewage in the pedestal foundation pit infiltrates into the nearby river outside the pedestal foundation pit through the leakage points, polluting the river water quality.

[0003] When the foundation pit is excavated to the middle sand layer and the silty silt sand layer and silty silty clay layer below it, the groundwater pressure causes water leakage and sand gushing in the middle sand layer and silty silt sand layer with good permeability, causing the soil on the outer wall of the foundation pit to leak out with an area of ​​1 to 3 m 2 The funnel-shaped subsidence area and the existing concrete ground became hollow, posing a huge safety hazard to the bridge pier construction.

[0004] The commonly used methods for plugging water leakage are: plugging the seams at the water leakage points of steel sheet piles and welding steel plates for reinforcement, sprinkling cement sand powder on the outside of steel sheet piles, pouring cement double slurry on the outside of steel sheet piles, backfilling clay in the funnel-shaped subsidence area, etc. These methods have the following technical defects: high risk of electric shock during welding operation in a humid environment, poor water leakage plugging effect, high cost of cement double slurry grouting, low clay bearing capacity in the liquefied state and small lateral support force. The above-mentioned water leakage plugging methods can no longer meet the requirements for water leakage plugging construction of composite cofferdams in foundation pits in large-area funnel-shaped subsidence areas.

[0005] Therefore, in the construction of the bridge pedestal foundation pit, how to develop a construction method for plugging water leakage in the foundation pit cofferdam that is simple in construction operation, fast in plugging water leakage, economical and reasonable, and safe and feasible is an urgent problem that needs to be solved for the safe construction of the bridge pedestal. Summary of the invention

[0006] The present invention provides a construction method for plugging water seepage in a composite cofferdam of a foundation pit in a funnel-shaped subsidence area, so as to solve the technical problems existing in the existing treatment methods, such as high risk of electric shock during welding operation in a humid environment, poor effect of plugging water seepage, high cost of cement double-slurry grouting, low bearing capacity of clay in a liquefied state and small lateral supporting force.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A construction method for plugging water seepage in a composite cofferdam of a foundation pit in a funnel-shaped subsidence area, comprising the following steps: material preparation and inspection: preparing and inspecting a variety of filling materials for plugging filling; breaking before construction: breaking existing cement mixing piles outside the composite cofferdam, the existing concrete floor and the existing concrete drainage ditch on the top of the subsidence area and the non-sinking area outside the subsidence area, so as to expose the existing cement mixing piles and the soil layer outside the foundation pit; steel sheet pile insertion: inserting and driving steel sheet piles downward in the subsidence area and the non-sinking area outside the subsidence area, so as to divide the subsidence area into an inner plugging treatment area and an outer plugging treatment area arranged in sequence front and back, and making the lateral sides of the steel sheet piles sealed and connected to the existing cement mixing piles respectively, so that the inner plugging treatment area forms an inner closed filling area closed along the circumferential direction; plugging filling construction: filling the inner closed filling area and the outer plugging treatment area with filling materials prepared by the filling materials; back pouring after filling: back pouring concrete on the top of the filling materials, the soil layer outside the foundation pit and the existing cement mixing piles to form a concrete floor and a concrete drainage ditch.

[0009] Furthermore, the steel sheet pile includes a plurality of first pile bodies and second pile bodies, and two third pile bodies; the first pile body, the second pile body and the third pile body have the same structure, and all include a steel sheet pile body with a "U"-shaped cross-section, and two lock buckles connected to both sides of the open end of the steel sheet pile body.

[0010] Furthermore, after completing the step of "breaking down before construction" and before carrying out the step of "inserting steel sheet piles", the method also includes the following steps: installing the inserting guide rods: fixing two inserting guide rods which are arranged in parallel and at intervals and span the subsidence area on the existing concrete ground in the non-sinking area outside the subsidence area, and each inserting guide rod extends in the lateral direction of the steel sheet piles to be inserted.

[0011] Furthermore, the step of "steel sheet pile driving" specifically includes: preparing a first pile body, a second pile body and a third pile body; using a steel sheet pile driving machine, hoisting a first pile body between two driving guide rods, and making the end face of the web of the first pile body close to the driving guide rod located at the rear position, and then driving the first pile body vertically downward into the silty silty clay layer below; then hoisting a second pile body between the two driving guide rods, and making the end face of the web of the second pile body close to the driving guide rod located at the front position, and then driving the second pile body vertically downward into the silty silty clay layer below, and connecting and interlocking with the previous first pile body. ; Then, the first pile body and the second pile body are driven in sequence along the horizontal direction of the steel sheet pile in a head-to-tail manner, and the first pile body and the second pile body are arranged in a staggered manner relative to each other and connected head-to-tail, and are locked and engaged with each other, and the opening direction of the second pile body is opposite to the opening direction of the first pile body; remove the two driving guide rods, and obliquely intersect the second pile body at an inclination angle on both sides of the horizontal side of the steel sheet pile, and vertically drive a third pile body downward into the silty clay layer, and make the lock on one side of the third pile body seal and abut against the existing cement mixing pile, and the lock on the other side abut against the lock on the outside of the second pile body and interlock.

[0012] Furthermore, when driving the first, second, ... Nth second pile, align the lock buckle of the second pile body with the lock buckle of the previous first pile body, and after they are interlocked with each other, start the vibratory hammer to gently hammer the second pile body first, so that it is 1 to 2 meters into the ground, and then observe the vertical verticality and horizontal position of the second pile body to see if they are qualified, and then continue to hammer the second pile body into the ground until the set depth; when driving the second, third, ... Nth first pile, align the lock buckle of the first pile body with the lock buckle of the previous second pile body, and after they are interlocked with each other, start the vibratory hammer to gently hammer the first pile body first, so that it is 1 to 2 meters into the ground, and then observe the vertical verticality and horizontal position of the first pile body to see if they are qualified, and then continue to hammer the first pile body into the ground until the set depth.

[0013] Furthermore, in the step of "material preparation and inspection", the filling materials include: crushed stone, fine sand, bentonite, quicklime powder and clay.

[0014] Furthermore, in the step of "leakage plugging and filling construction", the filling material prepared from the filling material includes: lime crushed stone clay material, fine sand material, mud material and lime clay material.

[0015] Furthermore, the step of "plugging and filling construction" specifically includes: filling lime gravel clay material in the middle of the inner closed filling area along the horizontal direction, filling fine sand material in both sides of the lime gravel clay material along the horizontal direction, filling mud material on the outside of the fine sand material, and filling lime clay material in the outer plugging treatment area.

[0016] Furthermore, when filling the filling materials, lime crushed stone clay material, fine sand material and lime clay material are filled simultaneously, and all three are filled in layers from bottom to top, and the mud material is filled later; after the filling is completed, the bottom ends of all the filling materials extend into the silty clay layer by 250 to 400 mm, and the top ends of all the filling materials are flush with the top ends of the existing cement mixing piles and the surface of the soil layer outside the foundation pit.

[0017] Furthermore, after completing the step of "leakage plugging and filling construction" and before carrying out the step of "back pouring after filling", the step is also included: leak plugging effect inspection.

[0018] The present invention has the following beneficial effects:

[0019] In the leakage plugging construction method of the present invention, by inserting and driving steel sheet piles, firstly, the funnel-shaped subsidence area is divided into an inner plugging treatment area and an outer plugging treatment area which are arranged in sequence in front and behind, and the steel sheet piles are also connected to the existing cement mixing piles to enclose the inner plugging treatment area with the composite cofferdam to form an inner closed filling area similar to the shape of a "mouth", so as to facilitate the zoning plugging construction of leakage water in the funnel-shaped subsidence area; secondly, when filling the funnel-shaped subsidence area, the skeleton function of the steel sheet pile is brought into play, so that it and the filling material of the inner closed filling area and the filling material of the outer plugging treatment area together form a high-strength filling whole, so as to push the composite cofferdam and the outer soil layer 5 of the foundation pit in the back, thereby improving the lateral support force of the outer side of the composite cofferdam; thirdly, When filling the funnel-shaped subsidence area, the steel sheet piles play a water-stopping role, and together with the filling material of the inner closed filling area and the filling material of the outer plugging treatment area, they form a multi-layer water-stopping filling system of flexible, semi-rigid and rigid alternating arrangements, which are arranged in sequence from the outer side of the foundation pit of the pedestal toward the inner side of the foundation pit of the pedestal: semi-rigid outer plugging treatment area filling material → flexible steel sheet piles → semi-rigid inner closed filling area filling material → rigid existing cement mixing piles → flexible existing steel sheet piles. Together, they stop the groundwater outside the composite cofferdam from infiltrating into the inner side of the composite cofferdam in the horizontal, vertical and up and down directions with the leakage point as the center, and also stop the construction sewage inside the composite cofferdam from seeping out of the river adjacent to the outer side of the composite cofferdam and polluting the river water quality.

[0020] On the other hand, by horizontally filling the filling material in the inner plugging treatment area to form a transverse filling layer, filling the filling material in the outer plugging treatment area to form a longitudinal filling layer, embedding the bottom ends of the transverse filling layer and the longitudinal filling layer into the silty silty clay layer at the bottom of the outer side of the composite cofferdam, and back-pouring concrete on the top of the filling material, the outer soil layer of the foundation pit and the existing cement mixing piles to form a concrete floor and a concrete drainage ditch, an overall seepage water plugging structure is formed to achieve transverse, longitudinal and up and down leakage plugging of groundwater and surface water outside the composite cofferdam with the leakage point as the center. Therefore, the water seepage plugging construction method of the present invention does not need to carry out the following construction steps: plugging the seams at the water seepage points of the steel sheet piles and welding the steel plates for reinforcement, sprinkling cement sand powder on the outside of the steel sheet piles, pouring cement double slurry on the outside of the steel sheet piles, backfilling clay in the funnel-shaped subsidence area, etc. It can effectively solve the technical problems of high risk of electric shock during welding operation in a humid environment, poor water seepage plugging effect, high cost of cement double slurry grouting, low clay bearing capacity in the liquefied state and small lateral supporting force. In addition, the water seepage plugging construction process is simple to operate, has low construction cost, and is easy to be widely promoted and used.

[0021] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0023] Figure 1 It is a construction flow chart of a construction method for plugging water seepage in a composite cofferdam of a foundation pit in a funnel-shaped subsidence area according to a preferred embodiment of the present invention;

[0024] Figure 2 It is a top view of the seepage plugging construction of the composite cofferdam of the funnel-shaped subsidence area foundation pit according to the preferred embodiment of the present invention;

[0025] Figure 3 yes Figure 2 Cross-section along the Ⅰ-Ⅰ axis.

[0026] Legend:

[0027] 1. Capping foundation pit; 2. Existing steel sheet piles; 3. Existing cement mixing piles; 4. Existing concrete floor; 5. Soil layer outside the foundation pit; 6. Water leakage point; 7. Steel sheet piles; 701. First pile body; 702. Second pile body; 703. Third pile body; 8. Subsidence area; 9. Lime gravel clay material; 10. Fine sand material; 11. Mud material; 12. Lime clay material; 13. Silty clay layer; 14. Concrete floor. DETAILED DESCRIPTION

[0028] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered below.

[0029] Reference Figure 1-3 The preferred embodiment of the present invention provides a construction method for plugging water seepage in a composite cofferdam of a foundation pit in a funnel-shaped subsidence area, comprising the following steps:

[0030] Material preparation and inspection: prepare and inspect various filling materials for plugging and filling;

[0031] Demolition before construction: Demolish the existing cement mixing piles 3 outside the composite cofferdam, the subsidence area 8 and the existing concrete floor 4 and the existing concrete drainage ditch on the top of the non-sinking area outside the subsidence area 8, so that the existing cement mixing piles 3 and the outer soil layer 5 of the foundation pit are exposed;

[0032] Steel sheet piles 7 are inserted and driven downward in the subsidence area 8 and the non-sinking area outside the subsidence area 8, so as to separate the subsidence area 8 into an inner plugging treatment area and an outer plugging treatment area which are sequentially arranged in front and behind, and the two lateral sides of the steel sheet piles 7 are respectively sealed and connected to the existing cement mixing piles 3, so that the inner plugging treatment area forms an inner closed filling area which is closed along the circumferential direction;

[0033] Leakage plugging and filling construction: Fill the inner closed filling area and the outer leak plugging treatment area with the filling materials prepared from the filling materials;

[0034] Back-pouring after filling: Back-pouring concrete on the filling material, the outer soil layer 5 of the foundation pit and the top of the existing cement mixing piles 3 to form a concrete floor 14 and a concrete drainage ditch.

[0035] In the seepage water plugging construction method of the present invention, by inserting and driving the steel sheet piles 7, firstly, the funnel-shaped subsidence area 8 is divided into an inner plugging treatment area and an outer plugging treatment area which are arranged in sequence in front and behind, and the steel sheet piles 7 are also connected to the existing cement mixing piles 3, so as to enclose the inner plugging treatment area with the composite cofferdam to form an inner closed filling area similar to the shape of a "mouth", so as to facilitate the zoning plugging construction of the seepage water in the funnel-shaped subsidence area 8; secondly, when the funnel-shaped subsidence area 8 is filled, the skeleton role of the steel sheet piles 7 is brought into play, so that it and the filling material of the inner closed filling area and the filling material of the outer plugging treatment area together form a high-strength filling whole, so as to squeeze and push the composite cofferdam and the outer soil layer 5 of the foundation pit in the back, thereby improving the lateral support force of the outer side of the composite cofferdam; thirdly, when the funnel-shaped subsidence area 8 is filled, the steel sheet piles 7 are used as a skeleton, so that they can form a high-strength filling whole together with the filling material of the inner closed filling area and the filling material of the outer plugging treatment area, so as to squeeze and push the composite cofferdam and the outer soil layer 5 of the foundation pit in the back, thereby improving the lateral support force of the outer side of the composite cofferdam; thirdly, when the funnel-shaped subsidence area 8 is filled, the steel sheet piles 7 are used as a skeleton, so that the steel sheet piles 7 can be ... When the funnel-shaped subsidence area 8 is filled, the steel sheet piles 7 play a water-stopping role, so that they, together with the filling material of the inner closed filling area and the filling material of the outer leak-proof treatment area, constitute a multi-layer water-stopping filling system of flexible, semi-rigid and rigid alternating arrangements, which are arranged in sequence from the outer side of the foundation pit 1 toward the inner side of the foundation pit 1: semi-rigid outer leak-proof treatment area filling material → flexible steel sheet piles 7 → semi-rigid inner closed filling area filling material → rigid existing cement mixing piles 3 → flexible existing steel sheet piles 2. Together, they stop the groundwater outside the composite cofferdam from infiltrating into the inner side of the composite cofferdam in the horizontal, vertical and up and down directions with the leakage point 6 as the center, and also stop the construction sewage inside the composite cofferdam from seeping out of the river adjacent to the outer side of the composite cofferdam and polluting the river water quality.

[0036] On the other hand, by horizontally filling the filling material in the inner plugging treatment area to form a transverse filling layer, filling the filling material in the outer plugging treatment area to form a longitudinal filling layer, embedding the bottom ends of the transverse filling layer and the longitudinal filling layer into the silty clay layer at the bottom of the outer side of the composite cofferdam, and back-pouring concrete on the top of the filling material, the outer soil layer 5 of the foundation pit and the existing cement mixing piles 3 to form a concrete floor and a concrete drainage ditch, an overall seepage water plugging structure is formed to achieve transverse, longitudinal and up and down leakage plugging of groundwater and surface water outside the composite cofferdam with the leakage point 6 as the center. Therefore, the water seepage plugging construction method of the present invention does not need to carry out the following construction steps: plugging the seams at the water seepage points of the steel sheet piles and welding the steel plates for reinforcement, sprinkling cement sand powder on the outside of the steel sheet piles, pouring cement double slurry on the outside of the steel sheet piles, backfilling clay in the funnel-shaped subsidence area, etc. It can effectively solve the technical problems of high risk of electric shock during welding operation in a humid environment, poor water seepage plugging effect, high cost of cement double slurry grouting, low clay bearing capacity in the liquefied state and small lateral supporting force. In addition, the water seepage plugging construction process is simple to operate, has low construction cost, and is easy to be widely promoted and used.

[0037] Optionally, the specific operation of the step "demolition before construction" is: Figure 2As shown, the composite cofferdam includes existing steel sheet piles 2, existing cement mixing piles 3, existing concrete floor 4 and existing concrete drainage ditch; at the top of the existing cement mixing piles 3 and the top of the subsidence area 8, the existing concrete floor 4 and the existing concrete drainage ditch are broken and extended to the non-sinking area by 5m respectively; the broken concrete blocks and concrete slag are cleaned to expose the existing cement mixing piles 3 and the outer soil layer 5 of the foundation pit.

[0038] Alternatively, if Figure 2 As shown, the steel sheet pile 7 includes a plurality of first pile bodies 701 and second pile bodies 702, and two third pile bodies 703; the first pile body 701, the second pile body 702 and the third pile body 703 have the same structure, and all include a steel sheet pile body with a "U"-shaped cross-section, and two lock buckles connected to both sides of the open end of the steel sheet pile body. In this optional solution, the steel sheet pile 7 adopts PU600×210×18mm steel sheet pile with a material of Q355P and a length of 18m. The steel sheet pile consists of a web, a wing plate and a lock, wherein: one end of the wing plate is welded to the lock, and the other end is welded to any end of the web to form a "U" shape. The lock end is arranged away from the web, and the opening direction of the steel sheet pile is opposite to the opening direction of the lock. The quality of the steel sheet pile meets the requirements of the "Hot Rolled Steel Sheet Piles" (GB / T20933) standard. If there are damaged piles or piles with inappropriate locks, the deformation must be corrected to make the size correct and the lock mouth smooth without bending. The quality inspection standard for smooth lock mouth is to use a pile body with a length of 1m to cover each group of steel sheet piles 7, and those that can pass smoothly are judged as qualified; the reverse "U-shaped protrusion" design of the lock buckles on both sides of each steel sheet pile body is used to interlock adjacent piles to form an interlocking structure. When the pile bodies are interlocked, a watertight structure is formed, thereby increasing the strength of the cofferdam structure of the steel sheet pile 7.

[0039] Preferably, after completing the step of "breaking before construction" and before carrying out the step of "inserting the steel sheet pile 7", the following steps are also included:

[0040] Installation of driving guide rods: Two driving guide rods are fixed on the existing concrete floor 4 in the non-sinking area outside the sinking area 8, which are arranged in parallel and spaced apart and cross the sinking area 8, and each driving guide rod extends in the lateral direction of the steel sheet pile 7 to be driven. Specifically, Figure 2As shown, on the existing concrete floor 4 in the non-sinking area on both sides of the sinking area 8, starting from the position 150-300mm away from the outside of the existing cement mixing pile 3, the first and second [200×75×9mm channel steels are installed in sequence in parallel with the existing cement mixing pile 3, so that the lower leg end faces of the first channel steel and the second channel steel are placed on the existing concrete floor 4, and the waist end faces of the first channel steel and the second channel steel are perpendicular to the existing concrete floor 4, and the two waist end faces face each other. The spacing is 460mm; then, drill holes and implant 2 φ20mm expansion bolts on the existing concrete floor 4 on both sides of each channel steel, close to the channel steel, to ensure that the channel steel is stable and does not shift laterally; after the channel steel is installed, make the first channel steel and the second channel steel span the top surface of the funnel-shaped subsidence area 8, that is, form a driving guide frame for the steel sheet piles 7; after the driving guide frame is installed, ensure that the steel sheet piles 7 are in a straight line laterally after being driven, so that the steel sheet piles 7 are locked tightly without water seepage in the gaps.

[0041] Optionally, the step of "inserting the steel sheet pile 7" specifically includes:

[0042] Prepare a first pile body 701, a second pile body 702 and a third pile body 703;

[0043] Use the steel sheet pile 7 driving machine to hang a first pile body 701 between the two driving guide rods, and make the web end face of the first pile body 701 close to the driving guide rod at the rear position, and then drive the first pile body 701 vertically downward into the silty silty clay layer 13 below; then hang a second pile body 702 between the two driving guide rods, and make the web end face of the second pile body 702 close to the driving guide rod at the front position, and then drive the second pile body 702 vertically downward into the silty silty clay layer 13 below; It is driven down into the silty clay layer 13 below and connected and interlocked with the previous first pile body 701; then the first pile body 701 and the second pile body 702 are driven in sequence along the horizontal direction of the steel sheet pile 7 in an end-to-end manner, and the first pile body 701 and the second pile body 702 are arranged in a staggered manner relative to each other and connected end-to-end, and are locked and engaged with each other, and the opening direction of the second pile body 702 is opposite to the opening direction of the first pile body 701.

[0044] Remove the two driving guide rods, and at the two lateral ends of the steel sheet pile 7, each of which is obliquely intersected with the second pile body 702 at an inclination angle, drive a third pile body 703 vertically downward into the silty clay layer 13, and make the lock buckle on one side of the third pile body 703 seal against the existing cement mixing pile 3, and the lock buckle on the other side abuts against the lock buckle on the outside of the second pile body 702 and interlocks; specifically, after the third pile body 703 is driven, it is obliquely intersected with the second pile body 702 at an angle of 135° or 45°. In this optional solution, the first pile body 701, the second pile body 702, the third pile body 703 and the existing cement mixing pile 3 enclose a similar "mouth"-shaped internal plugging treatment area.

[0045] Preferably, if Figure 2 As shown, when the first, second, ... Nth second pile body 702 is inserted, the lock buckle of the second pile body 702 is aligned with the lock buckle of the previous first pile body 701, and after they are engaged with each other, the second pile body 702 is gently hammered with a vibrating hammer to make it penetrate 1 to 2 meters into the soil. After the vertical verticality and horizontal position of the second pile body 702 are observed to be qualified, the second pile body 702 is hammered into the soil until the set depth is reached. The second, third, ... Nth first pile body 701 is inserted. 1, align the lock of the first pile body 701 with the lock of the previous second pile body 702, and after they are engaged with each other, turn on the vibrating hammer to gently hammer the first pile body 701 to make it penetrate 1 to 2 meters into the soil, and then observe whether the vertical verticality and horizontal position of the first pile body 701 are qualified, and then continue to hammer the first pile body 701 into the soil until the set depth; in this preferred embodiment, two total stations (or plumb bobs) are used to control the vertical verticality and plane position deviation of the steel sheet pile 7 in two directions.

[0046] Preferably, if Figure 2 As shown, after the steel sheet pile 7 is driven, the steel sheet pile 7 is made to be in a straight line shape horizontally, preventing the steel sheet pile 7 from being in an "S" shape, causing the steel sheet pile 7 to be locked or disengaged, resulting in water seepage at the lock of the steel sheet pile 7; and the top elevation of the steel sheet pile 7 is flush with the top elevation of the existing steel sheet pile 2, and the top elevation of the steel sheet pile 7 is 500mm higher than the top elevation of the existing cement mixing pile 3, and the bottom elevation of the steel sheet pile 7 is flush with the bottom elevation of the existing steel sheet pile 2; and the steel sheet pile 7 is driven horizontally and extended to the non-sinking area 4m.

[0047] Optionally, in the step "material preparation and inspection", the filling materials include: crushed stone, fine sand, bentonite, quicklime powder and clay. The specific requirements are as follows:

[0048] 1. Crushed stone: Made of hard granite, it is crushed into a continuous grade of 5 to 31.5 mm. Its quality meets the technical requirements for Class III crushed stone in the standard of Pebbles and Crushed Stone for Construction (GB / T14685).

[0049] 2. Fine sand: The machine-made sand is made from hard granite through crushing. The test results show that the fineness modulus is 1.8 and the particle size distribution is machine-made sand zone III. Its quality meets the technical requirements for Class III fine sand in the standard "Construction Sand" (GB / T14684).

[0050] 3. Bentonite: Bentonite produced in Hunan has a particle size of 325 mesh or 0.0450mm and a density of 1.80g / cm 3 , bulk density is 0.83g / cm 3The quality of the yellow powder sodium bentonite meets the requirements for drilling-grade bentonite in the "Benzonite" (GB / T 20973) standard, and its dosage is 8-10% of the mixing water mass.

[0051] The chemical composition of sodium bentonite is aluminum oxide, silicon dioxide and water, and the main component of sodium bentonite is montmorillonite, which is composed of three layers of Si-Al-Si overlapping. A large number of cations are adsorbed on the thin amorphous plate surface. When mixed with mixing water, the water quickly enters the crystal layer of montmorillonite, and the sodium bentonite expands rapidly, so that the small plate structure of the sodium bentonite is fully opened, and the bridging effect between the sodium bentonite and the high molecular polymer can be used on the wall surface of steel sheet pile 7, the wall surface of fine sand material 10, and the existing cement mixing pile 3 A mud skin is formed on the wall surface; sodium-based bentonite can be used to prepare a wall protection mud with a relatively large density and thick viscosity, which increases the lateral pressure of the mud on the wall surface of the steel sheet pile 7, the wall surface of the fine sand material 10, and the wall surface of the existing cement mixing pile 3, so that the finer particles in the mud penetrate into the pores of the adjacent fine sand material 10, the gaps in the pile body of the steel sheet pile 7, and the gaps in the existing cement mixing pile 3, and the coarser particles in the mud adhere to the wall surface of the steel sheet pile 7, the wall surface of the fine sand material 10, and the wall surface of the existing cement mixing pile 3 to form a thin, tough and dense mud skin.

[0052] 4. Quicklime powder: The quicklime powder has a particle size of 325 mesh or 0.0450 mm and a density of 3.35 g / cm 3 A white powdery substance; when natural rocks whose main component is calcium carbonate are calcined at an appropriate temperature and the decomposed carbon dioxide is removed, the product with calcium oxide (CaO) as the main component is lime, also known as quicklime.

[0053] 5. Clay: The clay is made of silty clay excavated from the foundation pit 1.

[0054] Alternatively, if Figure 2-3 As shown, in the step of “leakage plugging and filling construction”, the filling material prepared from the filling material includes: lime crushed stone clay material 9, fine sand material 10, mud material 11 and lime clay material 12.

[0055] Furthermore, if Figure 2-3 As shown, the step of "plugging and filling construction" specifically includes: filling the lime crushed stone clay material 9 in the middle of the inner closed filling area along the horizontal direction, filling the fine sand material 10 in both sides of the lime crushed stone clay material 9 along the horizontal direction, filling the mud material 11 in the outside of the fine sand material 10, and filling the lime clay material 12 in the outer plugging treatment area.

[0056] The leakage plugging structure of the present invention is constructed as follows:

[0057] (1) Horizontal seepage plugging: In the internal plugging treatment area, with the seepage point 6 as the center, limestone clay material 9, fine sand material 10 and mud material 11 are filled in parallel to form a horizontal filling layer to prevent the horizontal free flow of groundwater outside the composite cofferdam. The groundwater infiltrates into the foundation pit 1 through the horizontal filling layer and the seepage point 6, thereby plugging the horizontal seepage of groundwater outside the composite cofferdam with the seepage point 6 as the center.

[0058] (2) Longitudinal seepage water plugging: In the outer plugging treatment area, lime clay material 12 is filled to form a longitudinal filling layer to prevent the longitudinal free flow of groundwater outside the composite cofferdam and infiltrate into the inner plugging treatment area through the longitudinal filling layer, thereby plugging the longitudinal seepage water of the groundwater outside the composite cofferdam with the leakage point 6 as the center.

[0059] (3) Water leakage blocking in the vertical direction: At the bottom of the outer side of the composite cofferdam, the bottom ends of the horizontal filling layer and the vertical filling layer are embedded in the silty clay layer 13 by 250 to 400 mm; on the top of the horizontal filling layer, the vertical filling layer, the existing cement mixing piles 3 and the top surface of the outer soil layer 5 of the foundation pit at the top of the outer side of the composite cofferdam, concrete floors and concrete drainage ditches are poured to prevent the groundwater and surface water outside the composite cofferdam from flowing freely in the vertical direction and seeping into the inner side of the composite cofferdam through the horizontal filling layer, the vertical filling layer, the concrete floor and the leakage point 6, so as to block the vertical leakage of groundwater and surface water outside the composite cofferdam with the leakage point 6 as the center.

[0060] The plugging principle of the seepage water plugging structure of the present invention is as follows:

[0061] (1) The exothermic effect of quicklime and the volume expansion effect of clay absorbing water improve the lateral support and water-stopping performance: In the internal plugging treatment area, the areas 2.5 m to the left and right of the water leakage point 6 are filled with limestone clay materials 9 respectively; the quicklime absorbs water and reacts chemically with water to generate calcium hydroxide (Ca(OH)2) to release heat, promote the evaporation of water to form a crystalline structure, and improve the plate properties of the limestone clay material 9; and the clay absorbs water and expands in volume to fill the gaps between the gravels, thereby improving the density, compressive strength, bearing capacity and water-stopping performance of the limestone clay material 9, thereby improving the lateral support of the outer side of the composite cofferdam, preventing water from leaking at the locking point of the steel sheet pile 7, and infiltrating into the inner side of the composite cofferdam through the limestone clay material 9 and the water leakage point 6 to cause water accumulation, affecting the construction of the foundation pit 1, and also preventing the sewage from the construction inside the composite cofferdam from seeping into the river outside the composite cofferdam and polluting the river water quality.

[0062] (2) Filling the gaps with fine sand to improve water-stopping performance: In the internal plugging treatment area, the areas 1.5 m to the left and right of the limestone and gravel clay material 9 are filled with fine sand 10. Once groundwater flows outside the composite cofferdam, the fine sand will flow with the groundwater and flow into the gaps between the limestone and gravel clay materials 9, filling and compacting the limestone and gravel clay materials 9, thereby preventing the free flow of groundwater outside the composite cofferdam. At the same time, it also prevents construction wastewater inside the composite cofferdam from seeping into the nearby river outside the composite cofferdam and polluting the river water quality.

[0063] (3) Waterproofing of the wall slurry to improve water-stopping performance: In the "mouth"-shaped cavities on both sides of the fine sand material 10 in the non-sinking area of ​​the internal plugging treatment area, mixing water and bentonite are filled respectively, and the mixing water, bentonite, and the silty clay at the bottom of the foundation pit are mixed to prepare a wall slurry with high relative density and thick viscosity, thereby increasing the lateral pressure of the slurry on the wall surface of the steel sheet pile 7, the wall surface of the fine sand material 10, and the wall surface of the existing cement mixing pile 3, so that the finer particles in the slurry penetrate into the pores of the fine sand material 10, the locking gaps in the steel sheet pile 7, and the existing cement mixing pile 3. In the gap of cement mixing pile 3, coarser particles in the mud are attached to the wall surface of steel sheet pile 7, fine sand material 10 and existing cement mixing pile 3, forming a thin, tough and dense mud skin, which prevents groundwater outside the composite cofferdam from penetrating into the inner side of the composite cofferdam through steel sheet pile 7, mud material 11, fine sand material 10, lime gravel clay material 9 and seepage point 6 to cause water accumulation and affect the construction of foundation pit 1. At the same time, it also prevents construction sewage inside the composite cofferdam from seeping into the nearby river outside the composite cofferdam and polluting the river water quality.

[0064] (4) The heat release effect of quicklime and the volume expansion effect of clay absorbing water improve the board body, lateral support force and water-stopping performance: In the external plugging treatment area, the lime clay material 12 is filled, and the quicklime absorbs water and reacts chemically with water to generate calcium hydroxide (Ca(OH)2) to release heat, promote the evaporation of water to form a crystalline structure, and improve the board body of the lime clay material 12; and the clay absorbs water and expands in volume, thereby improving the density, compressive strength, bearing capacity and water-stopping performance of the lime clay material 12, thereby improving the lateral support force of the outer side of the composite cofferdam, preventing the groundwater outside the composite cofferdam from infiltrating into the inner plugging treatment area through the lime clay material 12 and the steel sheet piles 7, and also preventing the construction sewage inside the composite cofferdam from infiltrating into the river outside the composite cofferdam and polluting the river water quality.

[0065] Preferably, when filling the filling materials, the limestone clay material 9, the fine sand material 10 and the lime clay material 12 are filled synchronously, and the three are filled in layers from bottom to top, and the mud material 11 is filled later. After the filling is completed, the bottom ends of all the filling materials extend into the silty clay layer 13 by 250 to 400 mm, and the top ends of all the filling materials are flush with the top ends of the existing cement mixing piles 3 and the surface of the outer soil layer 5 of the foundation pit. The details are as follows:

[0066] (1) Simultaneous filling of limestone clay material 9 and fine sand material 10 in layers: In the inner plugging treatment area, the limestone clay material 9 and the fine sand material 10 are filled in layers simultaneously to ensure that the joints between each layer of limestone clay material 9 and the fine sand material 10 are tightly connected; after the limestone clay material 9 and the fine sand material 10 are filled, the limestone clay material 9 and the fine sand material 10 together form a high-strength filling whole, and at the same time, the composite cofferdam and the steel sheet piles 7 are squeezed and pushed in the back, thereby improving the lateral support force of the outer side of the composite cofferdam.

[0067] (2) Synchronous layered filling of the inner and outer plugging treatment areas: When the limestone gravel clay material 9 and fine sand material 10 are filled in the inner plugging treatment area, the limestone clay material 12 in the outer plugging treatment area must be filled simultaneously to maintain synchronous layered filling construction. The purpose is: first, to ensure that the steel sheet piles 7 do not tilt vertically or form an "S" shape horizontally after being squeezed and pushed in the inner and outer plugging treatment areas, causing the lock of the steel sheet pile 7 to be disengaged and leak water; second, after the limestone gravel clay material 9, fine sand material 10 and limestone clay material 12 are filled, the filling layer of the inner and outer plugging treatment areas together form a high-strength filling whole, and at the same time, the composite cofferdam and the outer soil layer 5 of the foundation pit are squeezed and pushed in reverse, thereby improving the lateral support force of the outer side of the composite cofferdam. Among them:

[0068] 1. Construction of filling with limestone and clay material 9: In the inner plugging treatment area, with the leakage point 6 as the center, the limestone and clay material 9 is filled in layers from the top surface of the silty clay layer 13 below the leakage point 6 to the top of the foundation pit 1, flush with the top of the existing cement mixing pile 3 and the top of the outer soil layer 5 of the foundation pit: after filling, the bottom of the limestone and clay material 9 is embedded in the silty clay layer 13 by 300mm, and the limestone and clay material 9 are filled in layers with a thickness of 300mm; wherein: the limestone and clay material 9 is prepared from quicklime powder, clay, and gravel in a mass percentage (by dry weight) of 10%: 20%: 70% to form limestone and clay; the gravel is a continuous grade gravel with a nominal grade of 5 to 31.5mm.

[0069] 2. Filling construction of fine sand material 10: In the internal plugging treatment area, with the lime gravel clay material 9 as the center, and the area 1.5m on both sides, start from the top surface of the silty clay layer 13 below the water leakage point 6, and fill the fine sand material 10 in layers to the top of the foundation pit 1, flush with the top of the existing cement mixing pile 3 and the top of the outer soil layer 5 of the foundation pit; after filling, the bottom end of the fine sand material 10 is embedded in the silty clay layer 13 by 300mm, and the layered thickness of the fine sand material 10 is 300mm; the fineness modulus of the fine sand in the fine sand material 10 is 1.8.

[0070] 3. Preparation of wall protection mud: In the non-sinking area within the internal plugging treatment area, use a special soil extractor to take out the outer soil layer 5 of the foundation pit to the "mouth"-shaped cavity on the top surface of the silty silty clay layer 13 at the bottom of the foundation pit. When taking out the outer soil layer 5 of the foundation pit, it is strictly forbidden to damage the fine sand material 10 adjacent to it; then fill the "mouth"-shaped cavity on both sides of the fine sand material 10 with mixing water and bentonite respectively, and use a special mixing tool to mix the mixing water, bentonite, and the silty silty clay at the bottom of the foundation pit to prepare the wall protection mud to the top of the foundation pit 1 of the foundation, flush with the top of the existing cement mixing pile 3 and the top of the outer soil layer 5 of the foundation pit, forming a mud material 11; wherein: the wall protection mud is composed of mixing water, bentonite, and silty silty clay in a mass ratio of 1000:90:10 (kg / m 3 ), and stirred to prepare the wall protection mud with relative density of 1.075-1.081, viscosity of 20.2-21.5 Pa·s, and mud skin thickness ≤2 (mm / 30min).

[0071] (3) Leakage plugging and filling construction in the external plugging treatment area: In the external plugging treatment area, lime clay material 12 is filled in layers from the top surface of the silty clay layer 13 below the leakage point 6 to the top of the foundation pit 1, flush with the top of the existing cement mixing pile 3 and the top of the outer soil layer 5 of the foundation pit; after filling, the bottom end of the lime clay material 12 is embedded in the silty clay layer 13 by 300 mm, and the lime clay material 12 is filled in layers with a thickness of 300 mm; wherein: the lime clay material 12 is prepared from quicklime powder and clay in a mass percentage (by dry weight) of 15%:85%.

[0072] Optionally, after completing the step of "leakage plugging and filling construction" and before performing the step of "re-pouring after filling", the following steps are further included:

[0073] Leakage plugging effect inspection. Specifically, on the inside of the existing steel sheet pile 2 of the composite cofferdam, with the leakage point 6 as the center, in the area of ​​6.0m on the left and right sides and 2.0m above and below, the seepage situation at the lock of each pile body was checked on the spot; the on-site inspection showed that the surface of the lock on the inside of the steel sheet pile 7 was dry and there was no water seepage, and the leakage plugging effect was good.

[0074] Optionally, the specific operation of the step "re-pouring after filling" is as follows:

[0075] 1. After the leakage plugging effect is checked and meets the requirements for foundation pit excavation, the top surfaces of lime gravel clay material 9, fine sand material 10, and lime clay material 12 are leveled, and the top surface of the mud material 11 is covered with a steel plate with a shape 0.3m larger than the plane size of the inner plugging treatment area and a thickness of 0.1m, so that the steel sheet pile 7 passes through the steel plate and is exposed to the same exposed height as the existing steel sheet pile 2, and the steel plate is welded firmly to the first pile body 701, the second pile body 702, and the third pile body 703 respectively.

[0076] 2. On the top surface of the lime crushed stone clay material 9, fine sand material 10, mud material 11 top steel plate, the existing cement mixing piles 3, lime clay material 12 and the outer soil layer 5 of the foundation pit in the non-sinking area outside the sinking area 8, pour a concrete floor 14 with the same thickness and the same strength grade as the existing concrete floor 4, so that the elevation of the concrete floor 14 is flush with the elevation of the existing concrete floor 4.

[0077] 3. On the poured concrete floor 14, pour a concrete drainage ditch of the same shape and strength grade as the existing concrete drainage ditch; the connection between the newly poured concrete drainage ditch and the existing concrete drainage ditch must be poured smoothly and densely to ensure that the surface water on the top of the foundation pit 1 does not penetrate into the inside of the composite cofferdam.

[0078] The scope of application of the seepage water plugging construction method of the present invention is as follows:

[0079] 1. The above scheme is a seepage plugging construction method for two seepage points in the composite cofferdam of the foundation pit in the funnel-shaped subsidence area. When there are more than two seepage points in the foundation pit cofferdam, the length of the inner plugging treatment area and the filling length of the lime gravel clay material 9 must be adjusted, and the filling length of the fine sand material 10 and the filling length of the mud material 11 remain unchanged, so that the seepage plugging of more than two seepage points in the foundation pit cofferdam can be completed.

[0080] 2. The above-mentioned water leakage plugging construction method, in addition to the bridge pedestal foundation pit construction field of the above-mentioned embodiment, can also be applied to the foundation pit construction of underground structure projects such as urban rail transit underground stations, underground pipe galleries, underground passages, underground culverts, industrial and civil building basements, etc.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A construction method for plugging water seepage in a composite cofferdam of a foundation pit in a funnel-shaped subsidence area, characterized in that: The following steps are involved: Material preparation and inspection: prepare and inspect various filling materials for plugging and filling; Demolition before construction: Demolition of the existing cement mixing piles (3) outside the composite cofferdam, the subsidence area (8) and the existing concrete floor (4) and the existing concrete drainage ditch on the top of the non-sinking area outside the subsidence area (8), so that the existing cement mixing piles (3) and the outer soil layer (5) of the foundation pit are exposed; Steel sheet pile (7) insertion: Steel sheet pile (7) is inserted downward in the subsidence area (8) and the non-sinking area outside the subsidence area (8) to separate the subsidence area (8) into an inner plugging treatment area and an outer plugging treatment area which are arranged in sequence in the front and back, and the two lateral sides of the steel sheet pile (7) are respectively sealed and connected to the existing cement mixing pile (3) so that the inner plugging treatment area forms an inner closed filling area which is closed along the circumferential direction; Leakage plugging and filling construction: Fill the inner closed filling area and the outer leak plugging treatment area with the filling materials prepared from the filling materials; Back-pouring after filling: Back-pouring concrete on the top of the filling material, the soil layer outside the foundation pit (5) and the existing cement mixing piles (3) to form a concrete floor (14) and a concrete drainage ditch.

2. The construction method for plugging water leakage in a composite cofferdam for a foundation pit in a funnel-shaped subsidence area according to claim 1 is characterized in that: The steel sheet pile (7) comprises a plurality of first pile bodies (701) and second pile bodies (702), and two third pile bodies (703); The first pile body (701), the second pile body (702) and the third pile body (703) have the same structure, and all include a steel sheet pile body with a "U"-shaped cross-section, and two lock buckles connected to both sides of the open end of the steel sheet pile body.

3. The construction method for plugging water leakage in a composite cofferdam for a foundation pit in a funnel-shaped subsidence area according to claim 2 is characterized in that: After completing the step "removal before construction" and before carrying out the step "insertion of steel sheet piles (7)", the following steps are also included: Installation of driving guide rods: Two driving guide rods are fixed on the existing concrete floor (4) in the non-sinking area outside the sinking area (8) and are arranged in parallel and spaced apart and straddling the sinking area (8), and each driving guide rod extends in the transverse direction of the steel sheet pile (7) to be driven.

4. The construction method for plugging water seepage in a composite cofferdam for a foundation pit in a funnel-shaped subsidence area according to claim 3 is characterized in that: The step of "inserting the steel sheet pile (7)" specifically includes: Prepare a first pile body (701), a second pile body (702) and a third pile body (703); Using a steel sheet pile (7) driving machine, a first pile body (701) is hoisted between two driving guide rods, and the web end surface of the first pile body (701) is closely attached to the driving guide rod located at the rear, and then the first pile body (701) is driven vertically downward into the silty silty clay layer (13) below; Then, a second pile body (702) is hoisted between the two driving guide rods, and the web end surface of the second pile body (702) is placed close to the driving guide rod located in the front position, and then the second pile body (702) is vertically driven downward into the silty silty clay layer (13) below, and is connected and interlocked with the first pile body (701) in front; then, the first pile body (701) and the second pile body (702) are driven in sequence along the steel sheet pile 7 in a transverse manner, and the first pile body (701) and the second pile body (702) are arranged in a staggered manner and connected end to end, and are locked and connected with each other, and the opening direction of the second pile body (702) is opposite to the opening direction of the first pile body (701); The two driving guide rods are removed, and a third pile body (703) is driven vertically downward into the silty clay layer (13) at both lateral ends of the steel sheet pile (7) at an inclination angle to the second pile body (702), and the lock buckle on one side of the third pile body (703) is sealed against the existing cement mixing pile (3), and the lock buckle on the other side is abutted against the lock buckle on the outside of the second pile body (702) and interlocked.

5. The construction method for plugging water seepage in a composite cofferdam for a foundation pit in a funnel-shaped subsidence area according to claim 4 is characterized in that: When the first, second, ... Nth second pile body (702) is driven, the lock buckle of the second pile body (702) is aligned with the lock buckle of the previous first pile body (701), and after the two are engaged with each other, the second pile body (702) is lightly hammered with a vibrating hammer to be inserted into the soil by 1 to 2 m, and after the vertical verticality and horizontal position of the second pile body (702) are observed to be qualified, the second pile body (702) is further hammered into the soil until a set depth is reached; when the second, third, ... Nth first pile body (701) is driven, the lock buckle of the first pile body (701) is aligned with the lock buckle of the previous second pile body (702), and after the two are engaged with each other, the first pile body (701) is lightly hammered with a vibrating hammer to be inserted into the soil by 1 to 2 m, and after the vertical verticality and horizontal position of the first pile body (701) are observed to be qualified, the first pile body (701) is further hammered into the soil until a set depth is reached.

6. The construction method for plugging water seepage in a composite cofferdam for a foundation pit in a funnel-shaped subsidence area according to claim 1, characterized in that: In the step "Material preparation and inspection", the filling materials include: crushed stone, fine sand, bentonite, quicklime powder and clay.

7. The construction method for plugging water seepage in a composite cofferdam for a foundation pit in a funnel-shaped subsidence area according to claim 6 is characterized in that: In the step of "leakage plugging and filling construction", the filling material prepared from the filling material includes: limestone clay material (9), fine sand material (10), mud material (11) and lime clay material (12).

8. The construction method for plugging water seepage in a composite cofferdam for a foundation pit in a funnel-shaped subsidence area according to claim 7, characterized in that: The step of "leakage plugging and filling construction" specifically includes: filling limestone crushed stone clay material (9) in the middle of the inner closed filling area in the horizontal direction, filling fine sand material (10) in both sides of the limestone crushed stone clay material (9) in the horizontal direction, filling mud material (11) on the outside of the fine sand material (10), and filling limestone clay material (12) in the outer leakage plugging treatment area.

9. The construction method for plugging water leakage in a composite cofferdam for a foundation pit in a funnel-shaped subsidence area according to claim 8, characterized in that: When filling the filling material, the limestone clay material (9), the fine sand material (10) and the lime clay material (12) are filled simultaneously, and the three are filled in layers from bottom to top, and the mud material (11) is filled later; After the filling is completed, the bottom ends of all the filling materials extend into the silty clay layer (13) by 250 to 400 mm, and the top ends of all the filling materials are flush with the top ends of the existing cement mixing piles (3) and the surface of the soil layer (5) outside the foundation pit.

10. The construction method for plugging water seepage in a composite cofferdam for a foundation pit in a funnel-shaped subsidence area according to claim 1, characterized in that: After completing the step of "leakage plugging and filling construction" and before carrying out the step of "back pouring after filling", the following steps are also included: Check the plugging effect.

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