A drainage construction method for deep foundation pit lowering plate area in water-rich areas

Abstract

The present invention discloses a drainage construction method for a lowering plate area of ​​a deep foundation pit in a water-rich area. The method is mainly used when the water level in the lowering plate area of ​​a local deep foundation pit is relatively high and the foundation pit operation requires dewatering. The drainage part is arranged at the bottom of the foundation pit, separated by an isolation film and a concrete sealing layer is arranged on the upper part thereof to form an independent drainage system. The water in the lower part of the sealing layer is discharged to the outside of the foundation pit through the drainage system, so as to achieve dynamic balance of the water level in the lower part of the foundation pit and provide a water-free working environment for the upper part of the sealing layer. The method can effectively and quickly solve the problem of dewatering in the lowering plate area of ​​a local deep foundation pit without setting a water-stop curtain. The method can achieve dynamic balance of the water level at the bottom of the foundation pit through the effective combination of structures / components such as seepage drainage blind pipes, drainage pipes, water pumps, and sealing layers. Compared with the traditional dewatering method, the method reduces the construction steps, shortens the construction period, improves the quality of foundation construction, and achieves the benefits of reducing costs and increasing efficiency.

Description

Technical Field

[0001] The invention belongs to the field of building construction, and in particular relates to a drainage construction method for a deep foundation pit lowering plate area in a water-rich area. Background Art

[0002] With the development of the construction industry, foundation pit dewatering is required when constructing foundation pits in areas with high groundwater levels. However, for situations where the groundwater level is below the base elevation of the non-dewatering area but above the base elevation of the deep foundation pit in the local dewatering area, since the excavation area of ​​the deep foundation pit in the local dewatering area is small, if traditional dewatering methods are used, such as water-stop curtains or pipe well point dewatering, the water level is lowered below the base elevation of the deep foundation pit before starting to excavate the foundation pit, the construction period is long and the cost is high. If large-scale dewatering is adopted, it will also affect the bearing capacity of the foundation pit foundation in the non-dewatering area. Summary of the Invention

[0003] The purpose of this patent is to provide a dewatering construction method for the lowering plate area of ​​deep foundation pits in water-rich areas to solve the problems arising from the above-mentioned background technology, that is, for the situation where the groundwater level is below the base elevation of the non-lowering plate area but above the base elevation of the deep foundation pit in the local lowering plate area, the dewatering method proposed in this patent can be used for dewatering construction. Compared with traditional dewatering methods, it can shorten the construction period, reduce construction costs, ensure the quality of foundation construction, minimize groundwater extraction, and ensure the stability of the foundation in the non-lowering plate area and the surrounding environment.

[0004] In order to solve the above technical problems, the inventors have come up with the technical solution of the present invention through practice and summary. The present invention adopts the following technical solution:

[0005] A method for drainage construction in a deep foundation pit drop slab area in a water-rich area, the construction steps are as follows:

[0006] S100: The foundation pit in the deep foundation pit drop-off area shall be excavated according to the drawing requirements. If groundwater appears during the excavation process, water pumps shall be used to pump out the water. The foundation pit shall be excavated to 400mm below the design elevation.

[0007] S200. After the foundation pit is excavated, drainage blind pipes are installed around the bottom. The blind pipes are 200mm stainless steel pipes with water holes on all four sides. The blind pipes on the four sides are connected end to end and do not communicate with each other.

[0008] The water pump is installed inside the blind pipe, and the water outlet of the water pump is welded with a 90° elbow to connect to the drain pipe. A float valve is installed in the blind pipe to control the start and stop of the water pump. When the water level in the blind pipe rises to a certain height, the water pump is controlled by the float valve to start pumping water;

[0009] The number and installation location of water pumps are determined according to the seepage location and amount of seepage at the bottom of the foundation pit. Generally, water pumps are installed at the corners and middle of the foundation pit, and an extra water pump needs to be set up as a reserve.

[0010] S300, the drainage pipe is connected from the foundation pit to the external sump. The sump is set in an area that does not affect the foundation construction. The size of the sump is excavated according to the site requirements. The drainage pipe is replaced with a water bag after it leaves the foundation pit.

[0011] After the water pump and drainage pipe are installed, start pumping water to keep the water level below the level of the pebble layer. Use the float valve to control the start and stop of the water pump to achieve dynamic balance of the water level.

[0012] S400. Lay a layer of pebbles around the blind pipe and at the bottom of the foundation pit. The pebble size should be between 20mm and 80mm. The pebbles need to be compacted during laying, and the compaction degree of the pebble layer must meet the design requirements.

[0013] A 0.4mm thick isolation film is laid on the top of the pebble layer as an isolation layer between the cushion layer and the pebble layer to prevent the concrete from entering the pebble layer and affecting the water permeability of the pebble layer during concrete pouring, and to prevent groundwater from affecting the strength of the concrete during concrete pouring;

[0014] After the foundation pit is excavated, an isolation membrane is laid on the slope of the foundation pit. The laying height is determined according to the height of the seepage point;

[0015] S500, pour a 200mm thick C20 concrete sealing layer on the isolation membrane, and pour a cushion layer on the foundation pit slope according to the design requirements to prevent sand flow, piping and slope instability under the action of dynamic water pressure;

[0016] The water in the lower part of the closed layer is discharged to the outside of the foundation pit through blind pipes and drainage pipes, forming an independent drainage system, achieving dynamic balance of the water level in the lower part of the foundation pit, and providing a water-free working environment for the upper part of the closed layer;

[0017] S600: After the construction of the part below the concrete sealing layer is completed, the stability of the foundation pit and the dynamic balance of the groundwater level are observed. After a period of observation, it is determined that the foundation pit slope is stable and the groundwater level is balanced, and the construction of the foundation pit raft slab begins;

[0018] During the construction process, it is necessary to continuously observe the groundwater level and the working condition of the water pump. If there is a water pump failure or a sudden increase in groundwater volume, start the backup water pump;

[0019] S700. After the construction of the foundation pit raft is completed, the blind pipes and drainage pipes are sealed. A grouting machine is used to inject grout into the gaps in the gravel layer and the blind pipes and drainage pipes through the drainage pipes. After the grouting is completed, the drainage pipe openings are sealed.

[0020] In the present invention, in step S700, a high-grade grouting agent is selected as the grouting material. After the grouting machine and materials are prepared as required, the specific construction steps are as follows:

[0021] 1) Drain pipes need to be blocked one by one. The blocking order is to block the pipes with smaller drainage volume first, and so on;

[0022] 2) First stop the water pump to be blocked, and continue the operation of the other water pumps. Cut off the drainage pipe at a position 50mm above the raft surface, insert the grouting pipe into the bottom of the drainage pipe, and seal the drainage pipe opening to form a static pressure space in the drainage pipe;

[0023] 3) Grouting begins. The grouting liquid enters the blind pipe through the drainage pipe, and is pressed into the pebble layer to fill the gaps in the pebble layer and the blind pipe within a certain range around the drainage pipe.

[0024] After observing the pressure of the grouting machine and the amount of grouting liquid injected, it is determined that the bottom grouting is completed, and then the seal of the drainage pipe opening is removed, and the grouting is continued until the grouting liquid overflows the drainage pipe opening and the grouting is completed;

[0025] 4) After the grouting is completed, the drainage pipe opening should be sealed to prevent water seepage and ensure that there will be no groundwater seepage through the drainage pipe in the later stage;

[0026] 5) Similarly, the remaining drainage pipes are sealed by grouting.

[0027] The drainage pipe described in the present invention is provided with a water stop plate, which is fixed on the lower side of the isolation film and a crimping sleeve is threadedly connected to the drainage pipe. The crimping sleeve and the water stop plate clamp the isolation film. A crimping rod is installed on the crimping sleeve, and a round rod is provided at the end of the crimping rod. The round rod is used to fix the isolation film at the root of the foundation pit.

[0028] When pouring the concrete sealing layer in step S500 of the present invention, the top of the sealing layer is assembled on the outside of the drainage pipe, and the top form of the sealing layer is vertically lowered to the top of the crimping sleeve by a lifting device. A grouting port is provided on the top form of the sealing layer, and a sealing plate is slidably installed at the grouting port. High-altitude grouting liquid is used to perform pressure grouting from the bottom to the top of the grouting port of the top form of the sealing layer through the grouting port to prevent the isolation film from deviating. After the grouting is completed, the grouting port is closed by sliding the sealing plate. After the concrete of the sealing layer reaches the design strength, it is lifted away from the top form of the sealing layer and disassembled.

[0029] In the present invention, a blocking structure is used to seal the drain pipe opening;

[0030] The blocking structure comprises:

[0031] The central cylindrical expansion member comprises a center disk and a center rod, the center rod is fixed to the upper surface of the center disk, and the center disk is slidably provided with an expansion plate 1 arranged left and right and an expansion plate 2 arranged front and back, a driving plate 1 is rotatably installed on the inner wall of the expansion plate 1, and a driving plate 2 is rotatably installed on the inner wall of the expansion plate 2, a limiting disk is fixed on the center rod, and a driving sleeve is sleeved on the center rod above the limiting disk, and the driving sleeve comprises an abutment disk and an axial disk, the abutment disk and the axial disk are connected by an elastic telescopic member, and a compression nut is threadedly connected on the center rod for squeezing the axial disk, the driving plate 1 is rotatably installed on the abutment disk, and the driving plate 2 is rotatably installed on the axial disk, and an elastic telescopic body is installed between the limiting disk and the abutment disk, and the elastic telescopic member begins to deform when the limiting disk and the abutment disk come into contact;

[0032] The rubber skin is fixed on the two expansion plates, and the outer wall of the rubber skin is provided with two groups of symmetrical water-stop corrugated surfaces.

[0033] The two ends of the expansion plate one described in the present invention are fixed with abutment plate one, and the two ends of the expansion plate two are fixed with abutment plate two. Abutment plate one and abutment plate two are both arranged vertically in the front and back direction. Under the indirect extrusion action of the compression nut, the expansion plate one and the expansion plate two form a cylindrical expansion structure and fix the rubber skin on the inner wall of the drain pipe.

[0034] Beneficial effects

[0035] The present invention provides a drainage construction method for the lowering plate area of ​​a deep foundation pit in a water-rich area. It is mainly used when the water level in the lowering plate area of ​​a local deep foundation pit is high and the foundation pit operation requires dewatering. The drainage part is arranged at the bottom of the foundation pit, separated by an isolation film and a concrete sealing layer is arranged on the upper part thereof to form an independent drainage system. The water in the lower part of the sealing layer is discharged to the outside of the foundation pit through the drainage system, so as to achieve dynamic balance of the water level in the lower part of the foundation pit and provide a water-free working environment for the upper part of the sealing layer. It can effectively and quickly solve the problem of dewatering in the lowering plate area of ​​a local deep foundation pit without setting a water-stop curtain. Through the effective combination of structures / components such as seepage drainage blind pipes, drainage pipes, water pumps, and sealing layers, the dynamic balance of the water level at the bottom of the foundation pit is achieved. Compared with the traditional dewatering method, the construction steps are reduced, the construction period is shortened, the quality of foundation construction is improved, and the benefits of cost reduction and efficiency improvement are achieved.

[0036] The present invention uses a top-mounted formwork to pressure-grout the concrete seal layer from bottom to top, effectively overcoming the tendency of the isolation membrane to deviate during traditional casting methods. A structure is also provided on the drain pipe to compress the isolation membrane for waterproofing. The top formwork of the seal layer is cast using a suspended hoisting method, which does not damage the isolation membrane. The top of the isolation membrane can also be fixed to the foundation pit (150mm above the seepage point). Furthermore, the present invention utilizes an internal expansion cylindrical structure in conjunction with rubber to effectively and quickly seal the drain pipe opening, enabling rapid sealing and avoiding the problem of poor structural durability caused by delayed sealing with traditional welded steel plates, resulting in high water seepage. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a top view of the overall structure of the present invention;

[0038] Figure 2 It is a vertical cross-sectional view of the overall structure of the present invention;

[0039] Figure 3 for Figure 2 A partial enlarged view of point A in the middle.

[0040] Figure 4 It is a front and rear cross-sectional view of the drainage pipe orifice blocking structure;

[0041] Figure 5 The left and right cross-sectional views of the drainage pipe orifice blocking structure;

[0042] Figure 6 This is the construction structure diagram of the closed layer. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0044] In the description of the present invention, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as limiting the present invention.

[0045] Example 1, as Figures 1 to 6 As shown, a method for drainage construction in the deep foundation pit drop plate area in water-rich areas, the construction steps are as follows:

[0046] S100: The foundation pit in the deep foundation pit drop-off area shall be excavated according to the drawing requirements. If groundwater appears during the excavation process, water pumps shall be used to pump out the water. The foundation pit shall be excavated to 400mm below the design elevation.

[0047] S200. After the foundation pit is excavated, drainage blind pipes 4 are set around the bottom. The blind pipes 4 are 200mm stainless steel pipes with water holes on all four sides. The blind pipes 4 on the four sides are connected end to end and do not communicate with each other.

[0048] The water pump is set inside the blind pipe 4, and the water outlet of the water pump is welded with a 90° elbow to connect to the drain pipe 3. A float valve is set in the blind pipe 4 to control the start and stop of the water pump. When the water level in the blind pipe 4 rises to a certain height, the water pump can start pumping water through the float valve.

[0049] The number and installation location of water pumps are determined according to the seepage location and amount of seepage at the bottom of the foundation pit. Generally, water pumps are installed at the corners and middle of the foundation pit, and an extra water pump needs to be set up as a reserve.

[0050] S300: Drain pipe 3 is connected from the foundation pit to an external sump 6. The sump 6 is set in an area that does not affect the foundation construction. The size of the sump 6 is excavated according to the site requirements. After the drain pipe 3 leaves the foundation pit, it is replaced with a water bag.

[0051] After the water pump and the drain pipe 3 are installed, they start pumping water to keep the water level below the elevation of the pebble layer 7. The water pump is started and stopped by the float valve to achieve dynamic balance of the water level.

[0052] S400, laying a pebble layer 7 around the blind pipe 4 and at the bottom of the foundation pit. The pebble particle size is required to be between 20 mm and 80 mm. The pebbles need to be compacted when laid, and the compaction degree of the pebble layer 7 must meet the design requirements;

[0053] A 0.4 mm thick isolation film 8 is laid on the top of the pebble layer 7 as an isolation layer between the cushion layer and the pebble layer 7 to prevent the concrete from entering the pebble layer 7 and affecting the water permeability of the pebble layer 7 during concrete pouring, and to prevent groundwater from affecting the strength of the concrete during concrete pouring;

[0054] After the foundation pit is excavated, an isolation film 8 is laid on the foundation pit slope. The laying height is determined according to the height of the seepage point.

[0055] S500, pouring a 200mm thick C20 concrete sealing layer 9 on the isolation membrane 8, and pouring a cushion layer on the foundation pit slope according to the design requirements to prevent the foundation pit from causing sand flow, pipe gushing and slope instability under the action of dynamic water pressure;

[0056] The water below the closed layer 9 is discharged to the outside of the foundation pit through the blind pipe 4 and the drainage pipe 3, forming an independent drainage system, achieving dynamic balance of the water level in the lower part of the foundation pit, and providing a water-free working environment above the closed layer 9;

[0057] S600: After the construction of the part below the concrete sealing layer 9 is completed, the stability of the foundation pit and the dynamic balance of the groundwater level are observed. After a period of observation, it is determined that the foundation pit slope is stable and the groundwater level is balanced, and the construction of the foundation pit raft slab begins;

[0058] During the construction process, it is necessary to continuously observe the groundwater level and the working condition of the water pump. If there is a water pump failure or a sudden increase in groundwater volume, start the backup water pump;

[0059] S700, after the construction of the foundation pit raft is completed, the blind pipe 4 and the drainage pipe 3 are blocked, and a grouting machine is used to inject grout into the gaps in the pebble layer 7 and the blind pipe 4 and the drainage pipe 3 through the drainage pipe 3 to block the gaps. After the grouting is completed, the opening of the drainage pipe 3 is sealed.

[0060] Among them, in step S700, the grouting material is selected as a high-grade grouting agent. After the grouting machine and materials are prepared as required, the specific construction steps are as follows:

[0061] 1) Drain pipes 3 need to be blocked one by one. The blocking order is to block the pipes with smaller drainage volume first, and so on.

[0062] 2) First, stop the water pump to be blocked, and continue the operation of the other water pumps. Cut off the drainage pipe 3 at a position 50mm above the raft surface, insert the grouting pipe into the bottom of the drainage pipe 3, and seal the drainage pipe 3 to form a static pressure space in the drainage pipe 3;

[0063] 3) Grouting begins. The grouting liquid enters the blind leg 4 through the drain pipe 3 and is pressed into the pebble layer 7 to fill the gaps in the pebble layer 7 and the blind leg 4 within a certain range around the drain pipe 3.

[0064] After observing the pressure of the grouting machine and the amount of grouting liquid injected, it is determined that the bottom grouting is completed, and then the seal of the drain pipe 3 is removed, and the grouting is continued until the grouting liquid overflows the drain pipe 3 and the grouting is completed;

[0065] 4) After the grouting is completed, the opening of the drainage pipe 3 is sealed to prevent water seepage and ensure that no groundwater will seep out through the drainage pipe 3 in the later stage;

[0066] 5) Similarly, the remaining drainage pipes 3 are grout-sealed.

[0067] Among them, a water stop plate 31 is provided on the drainage pipe 3, the water stop plate 31 is fixed on the lower side of the isolation film 8 and a crimping sleeve 32 is threadedly connected to the drainage pipe 3, the crimping sleeve 32 and the water stop plate 31 clamp the isolation film 8, and a crimping rod 33 is installed on the crimping sleeve 32. A round rod is provided at the end of the crimping rod 33, and the round rod is used to fix the isolation film 8 at the root of the foundation pit.

[0068] Among them, when pouring the concrete sealing layer 9 in step S500, the top of the sealing layer 9 is assembled on the outside of the drainage pipe 3, and the sealing layer top formwork 2 is vertically lowered to the top of the crimping sleeve 32 through the lifting equipment. A grouting port is provided on the sealing layer top formwork 2, and a sealing plate 21 is slidably installed at the grouting port. High-altitude grouting liquid is used to pressure-grout from the bottom to the top through the grouting port of the sealing layer top formwork 2 to prevent the isolation film 8 from deviating. After the grouting is completed, the grouting port is closed by sliding the sealing plate 21. After the concrete of the sealing layer 9 reaches the design strength, it is lifted away from the sealing layer top formwork 2 and disassembled.

[0069] Among them, a blocking structure is used when closing the outlet of the drainage pipe 3;

[0070] The blocking structure comprises:

[0071] The central cylindrical expansion member 1 includes a central disk 11 and a central rod 12. The central rod 12 is fixed to the upper surface of the central disk 11. The central disk 11 is slidably provided with an expansion plate 13 arranged left and right and an expansion plate 2 14 arranged front and back. A driving plate 15 is rotatably installed on the inner wall of the expansion plate 13, and a driving plate 2 16 is rotatably installed on the inner wall of the expansion plate 2 14. A limiting disk 17 is fixed on the central rod 12. A driving sleeve is mounted on the central rod 12 above the limiting disk 17. The driving sleeve includes an abutment disk 18 and an axial disk 19. The abutment disk 18 and the axial disk 19 are connected by an elastic telescopic member 110. The elastic telescopic member 110 is an interpenetrating rod inserted into the abutment disk 18 and the axial disk 19. The ends of the interpenetrating rods are fixed with blocks. The blocks are located on the back-to-back sides of the two and the interpenetrating rod between the two is provided with a spring, and the center rod 12 is provided with a spring. The threaded connection is provided with a compression nut 111 for squeezing the axial disk 19, the driving plate 15 is rotatably installed on the abutment disk 18, and the driving plate 2 16 is rotatably installed on the axial disk 19. An elastic telescopic body 112 is installed between the limit disk 17 and the abutment disk 18. The structure of the elastic telescopic body 112 is shown in the figure, including one end of the ring sleeve extending downward and a spring installed inside. The spring is sleeved on the outside of the center rod 12. After the elastic telescopic body 112 can no longer be deformed, the spring of the elastic telescopic member 110 begins to deform. In this way, during the deformation of the elastic telescopic body 112, the expansion plate 13 and the expansion plate 2 14 move outward together, so that the expansion plate 13 first presses the rubber skin 113 against the inner wall of the pipe orifice. After that, the spring of the elastic telescopic member 110 begins to deform, and the expansion plate 2 14 moves outward relative to the expansion plate 13 to press the rest of the rubber skin 113 against the inner wall of the pipe orifice.

[0072] The rubber skin 113 is fixed on the two expansion plates 13. The outer wall of the rubber skin 113 is provided with two sets of symmetrical water-stopping corrugated surfaces to improve the waterproof effect.

[0073] Among them, both ends of the expansion plate 13 are fixed with abutment plate 115, and both ends of the expansion plate 2 14 are fixed with abutment plate 2 114. Abutment plate 115 and abutment plate 2 114 are both arranged vertically in the front and back directions. Under the indirect extrusion action of the compression nut 111, the expansion plate 13 and the expansion plate 2 14 form a cylindrical expansion structure and fix the rubber skin 113 on the inner wall of the drain pipe 3.

[0074] By placing the center disk 11 and the center rod 12 in the pipe mouth, and by screwing the compression nut 111 toward the center disk 11, the abutment disk 18 and the axial disk 19 will be driven downward together, and the elastic telescopic body 112 will be pressed until it can no longer deform. At this time, the expansion plate 13 is in the state of pressing the rubber skin 113 on the inner wall of the pipe mouth. It continues to be screwed in, and the axial disk 19 will squeeze the spring relative to the expansion plate 13 to move outward. In this process, the spring of the elastic telescopic part 110 is deformed, and finally the rubber skin 113 is pressed tightly into the pipe mouth. At this time, the abutment plate 1 115 and the abutment plate 2 114 will be completely fitted together. The expansion plate 13 and the expansion plate 2 14 are in a cylindrical expansion structure under the indirect extrusion of the compression nut 111 and tightly press the rubber skin 113 against the inner wall of the drain pipe 3.

[0075] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. The replacement may be a replacement of a portion of a structure, device, or method step, or it may be a complete technical solution. Any equivalent replacement or modification based on the technical solution and inventive concept of the present invention shall be covered by the scope of protection of the present invention.

Claims

1. A method for drainage construction in a deep foundation pit drop plate area in a water-rich area, characterized in that: The construction steps are as follows: S100: The foundation pit in the deep foundation pit drop-off area shall be excavated according to the drawing requirements. If groundwater appears during the excavation process, water pumps shall be used to pump out the water. The foundation pit shall be excavated to 400mm below the design elevation. S200, after the foundation pit is excavated, drainage blind pipes (4) are set around the bottom. The blind pipes (4) are 200mm stainless steel pipes with water holes on all four sides. The four blind pipes (4) are connected end to end and do not communicate with each other; The water pump is arranged inside the blind pipe (4), and the water outlet of the water pump is connected to the drain pipe (3) by welding a 90° elbow. A float valve is arranged inside the blind pipe (4) to control the start and stop of the water pump. When the water level in the blind pipe (4) rises to a certain height, the water pump is controlled by the float valve to start pumping water. The number and installation location of water pumps are determined according to the seepage location and amount of seepage at the bottom of the foundation pit. Generally, water pumps are installed at the corners and middle of the foundation pit, and an extra water pump needs to be set up as a reserve. S300, the drainage pipe (3) is connected from the foundation pit to the external water collection pit (6), the water collection pit (6) is set in an area that does not affect the foundation construction, the size of the water collection pit (6) is excavated according to the site requirements, and the drainage pipe (3) is replaced with a water bag after leaving the foundation pit; After the water pump and the drainage pipe (3) are installed, water is pumped to keep the water level below the elevation of the pebble layer (7). The water pump is started and stopped by the float valve to achieve dynamic balance of the water level. S400, laying a pebble layer (7) around the blind pipe (4) and at the bottom of the foundation pit, the pebble particle size is required to be between 20mm and 80mm, the pebble needs to be compacted when laying, and the compaction degree of the pebble layer (7) needs to meet the design requirements; A 0.4 mm thick isolation film (8) is laid on the upper portion of the pebble layer (7) as an isolation layer between the cushion layer and the pebble layer (7) to prevent the concrete from entering the pebble layer (7) during concrete pouring and affecting the water permeability of the pebble layer (7), and to prevent the groundwater from affecting the strength of the concrete during concrete pouring; After the foundation pit is excavated, an isolation membrane (8) is laid on the slope of the foundation pit, and the laying height is determined according to the height of the seepage point; S500, pouring a 200mm thick C20 concrete sealing layer (9) on the isolation film (8), and pouring a cushion layer on the foundation pit slope according to the design requirements to prevent the foundation pit from causing sand flow, pipe bursts and slope instability under the action of dynamic water pressure; The water in the lower part of the closed layer (9) is discharged to the outside of the foundation pit through the blind pipe (4) and the drainage pipe (3), forming an independent drainage system, achieving a dynamic balance of the water level in the lower part of the foundation pit, and providing a water-free working environment for the upper part of the closed layer (9); S600, after the construction of the part below the concrete sealing layer (9) is completed, the stability of the foundation pit and the dynamic balance of the groundwater level are observed. After a period of observation, it is determined that the foundation pit slope is stable and the groundwater level is balanced, and the construction of the foundation pit raft slab begins; During the construction process, it is necessary to continuously observe the groundwater level and the working condition of the water pump. If there is a water pump failure or a sudden increase in groundwater volume, start the backup water pump; S700, after the construction of the foundation pit raft is completed, the blind pipe (4) and the drainage pipe (3) are blocked, and a grouting machine is used to grout the gaps in the pebble layer (7) and the blind pipe (4) and the drainage pipe (3) through the drainage pipe (3), and the drainage pipe (3) is sealed after the grouting is completed; A blocking structure is used when closing the outlet of the drainage pipe (3); The blocking structure comprises: The middle cylindrical expansion member (1) comprises a center disk (11) and a center rod (12), the center rod (12) is fixed on the upper surface of the center disk (11), and the center disk (11) is provided with a left-right expansion plate (13) and a front-back expansion plate (14) arranged for sliding, a driving plate (15) is rotatably mounted on the inner wall of the expansion plate (13), and a driving plate (16) is rotatably mounted on the inner wall of the expansion plate (14), a limiting disk (17) is fixed on the center rod (12), and a driving sleeve is mounted on the center rod (12) above the limiting disk (17). The movable sleeve includes an abutment disc (18) and an axial disc (19), the abutment disc (18) and the axial disc (19) are connected by an elastic telescopic member (110), and a compression nut (111) is threadedly connected to the center rod (12) for squeezing the axial disc (19), the driving plate 1 (15) is rotatably mounted on the abutment disc (18), the driving plate 2 (16) is rotatably mounted on the axial disc (19), an elastic telescopic body (112) is installed between the limiting disc (17) and the abutment disc (18), and the elastic telescopic member (110) begins to deform when the limiting disc (17) and the abutment disc (18) come into contact. The rubber skin (113) is fixed on the two expansion plates (13), and the outer wall of the rubber skin (113) is provided with two groups of symmetrical water-stopping corrugated surfaces; Both ends of the expansion plate 1 (13) are fixed with abutment plate 1 (115), and both ends of the expansion plate 2 (14) are fixed with abutment plate 2 (114). Abutment plate 1 (115) and abutment plate 2 (114) are both arranged vertically in the front-back direction. Under the indirect squeezing action of the compression nut (111), the expansion plate 1 (13) and the expansion plate 2 (14) form a cylindrical expansion structure and fix the rubber skin (113) to the inner wall of the drainage pipe (3).

2. The method for drainage construction in a deep foundation pit in a water-rich area according to claim 1 is characterized in that: In step S700, high-grade grouting agent is selected as the grouting material. After the grouting machine and materials are prepared as required, the specific construction steps are as follows: 1) Drain pipes (3) need to be blocked one by one, and the blocking order is to block the pipes with smaller drainage volume first, and so on; 2) First, stop the water pump to be blocked, and continue the operation of the other water pumps. Cut off the drainage pipe (3) at a position 50 mm above the raft surface, insert the grouting pipe into the bottom of the drainage pipe (3), and seal the drainage pipe (3) to form a static pressure space in the drainage pipe (3); 3) Grouting begins, the grouting liquid enters the blind pipe (4) through the drainage pipe (3), and the grouting liquid is pressed into the pebble layer (7), filling the gaps in the pebble layer (7) and the blind pipe (4) within a certain range around the drainage pipe (3); After observing the pressure of the grouting machine and the amount of grouting liquid injected, it is determined that the bottom grouting is completed, and then the seal of the drain pipe (3) is removed, and the grouting is continued until the grouting liquid overflows the drain pipe (3) and the grouting is completed; 4) After the grouting is completed, the outlet of the drainage pipe (3) is sealed to prevent water seepage, thereby ensuring that no groundwater will seep out through the drainage pipe (3) in the later stage; 5) Similarly, the remaining drainage pipes (3) are grout-sealed.

3. The method for drainage construction in a deep foundation pit in a water-rich area according to claim 2, characterized in that: The drainage pipe (3) is provided with a water stop disc (31), which is fixed to the lower side of the isolation film (8). A crimping sleeve (32) is threadedly connected to the drainage pipe (3), and the crimping sleeve (32) and the water stop disc (31) clamp the isolation film (8). A crimping rod (33) is installed on the crimping sleeve (32), and a round rod is provided at the end of the crimping rod (33). The round rod is used to fix the isolation film (8) at the root of the foundation pit.

4. A method for drainage construction in a deep foundation pit in a water-rich area according to claim 3, characterized in that: When pouring the concrete sealing layer (9) in step S500, the top of the sealing layer (9) is assembled on the outside of the drainage pipe (3), and the sealing layer top formwork (2) is vertically lowered to the top of the crimping sleeve (32) by a hoisting device. A grouting port is provided on the sealing layer top formwork (2), and a blocking plate (21) is slidably installed at the grouting port. High-altitude grouting liquid is pressure-grouted from the grouting port of the sealing layer top formwork (2) from the bottom to the top through the grouting port to prevent the isolation film (8) from deviating. After the grouting is completed, the grouting port is closed by sliding the blocking plate (21). After the concrete of the sealing layer (9) reaches the design strength, it is hoisted away from the sealing layer top formwork (2) and disassembled.

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