A local dynamic balance drainage construction method for deep foundation pits

Abstract

The present invention discloses a local dynamic balance dewatering construction method for a deep foundation pit. It is mainly used when the water level in the local deep foundation pit drop plate area is high and the foundation pit operation requires dewatering. The dewatering construction method is arranged at the bottom of the foundation pit, and a concrete sealing layer is arranged on the upper part to form an independent dewatering system. The water in the lower part of the sealing layer is discharged to the outside of the foundation pit through the dewatering construction method, 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 local deep foundation pit drop plate area without setting a water-stop curtain. The method achieves dynamic balance of the water level at the bottom of the foundation pit through the effective combination of seepage drainage blind pipes, drainage pipes, booster pumps, sealing layers and other equipment. 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 local dynamic balance drainage construction method for a deep foundation pit. 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, in the case 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 dewatering, the water level is lowered below the base elevation of the deep foundation pit before excavating 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 in the non-dewatering area. At the same time, some existing methods use pre-buried pipes to collect seepage water, and cooperate with water pumps to extract water for dewatering. However, the subsequent plugging requires rapid plugging, which cannot be completed effectively. When plugging the pipeline in the later stage, welded steel plates are often used for plugging. This will not be timely, resulting in a large amount of seepage and poor durability of the structure. Summary of the Invention

[0003] The purpose of the present invention is to provide a local dynamic balance dewatering construction method for deep foundation pits 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-dewatering area but above the base elevation of the deep foundation pit in the local dewatering area, the dewatering construction method proposed in the present invention 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, reduce groundwater extraction as much as possible, and ensure the stability of the foundation in the non-dewatering area and the surrounding environment.

[0004] The present invention adopts the following technical solutions:

[0005] A local dynamic balance drainage construction method for a deep foundation pit, 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 4 are installed around the bottom. The blind pipes 4 are 200 mm stainless steel pipes with water holes on all four sides. A movable pipe 41 is slidably installed inside the blind pipe 4. The movable pipe 41 is provided with water holes corresponding to the positions of the water holes and of equal size. One end of the movable pipe 41 is a blind head, and the outside of the blind head is provided with an elastic telescopic locking member. The four blind pipes 4 are connected end to end and do not communicate with each other.

[0008] The drainage pipe 3 is connected to the blind pipe 4. A water pump 5 is installed at the outlet end of the drainage pipe 4. A float valve is set in the blind pipe 4 to control the start and stop of the water pump 5. When the water level in the blind pipe 4 rises to a certain height, the water pump 5 can start pumping water by controlling the float valve.

[0009] The number and installation location of the 5 water pumps are determined according to the seepage location and amount of the foundation pit bottom on site. An extra water pump 5 needs to be installed.

[0010] S300: Drain pipe 3 is connected from the foundation pit to an external sump 6. The pump 5 is located outside the foundation pit. 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 site requirements. After the drain pipe 3 exits the foundation pit, it is replaced with a water bag.

[0011] After the water pump 5 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 5 is started and stopped by the float valve to achieve dynamic balance of the water level.

[0012] 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;

[0013] 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;

[0014] 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.

[0015] 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;

[0016] 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;

[0017] 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;

[0018] During the construction process, it is necessary to continuously observe the groundwater level and the working condition of the water pump 5. If there is a failure of the water pump 5 or the amount of groundwater increases suddenly, start the standby water pump 5;

[0019] 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.

[0020] Preferably, 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 3 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 pump 5 to be blocked, and continue the operation of the other pumps 5. 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.

[0023] 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.

[0024] After observing the pressure of the grouting machine and calculating 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;

[0025] 4) After the grouting is completed, the outlet of the drainage pipe 3 is sealed to ensure the welding quality and prevent water seepage, so as to ensure that groundwater will not seep out through the drainage pipe 3 in the later stage;

[0026] 5) Similarly, the remaining drainage pipes 3 are grout-sealed.

[0027] Preferably, a water stop plate 31 is provided on the drainage pipe 3, the water stop plate 31 is fixed to 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, 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, which is used to fix the isolation film 8 at the root of the foundation pit.

[0028] Preferably, 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 lifting device. 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 fluid is used to perform pressure grouting 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 detached.

[0029] Preferably, the elastic telescopic locking member includes a fixed tube 42, a movable rod and an elastomer. The fixed tube 42 is fixed to the inner side of the blind end of the blind tube 4, and the movable rod 43 rotates on the outer side of the blind head of the movable tube 41. Part of the movable rod 43 extends into the fixed tube 42 and is connected to the fixed tube 42 through a spring. A guide groove 44 is provided on the fixed tube 42, and a one-way conduction structure is provided at the root of the guide groove 44. A guide pin 45 is fixedly installed on the movable rod 43, and the guide pin 45 and the guide groove 44 are slidably fitted.

[0030] Preferably, the one-way conduction structure includes a fixing seat 46 arranged on the outside of the fixing tube 42, and a spring and a wedge block 47 are provided in the fixing seat 46. The wedge block 47 is slidably installed in the fixing seat 46 through the spring, and the wedge block 47 partially extends to the outside of the guide groove 44 for one-way locking and fixing the guide pin 45.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The patent provides a local dynamic balance drainage construction method for deep foundation pits. It is mainly used when the water level in the local deep foundation pit drop plate area is high and the foundation pit operation requires dewatering. The dewatering construction method is set at the bottom of the foundation pit, and a concrete sealing layer is set on the upper part to form an independent dewatering system. The water in the lower part of the sealing layer is discharged to the outside of the foundation pit through the dewatering construction method, 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 local deep foundation pit drop plate area without setting up a water-stop curtain. Through the effective combination of seepage drainage blind pipes, drainage pipes, booster pumps, sealing layers and other equipment, the dynamic balance of the water level at the bottom of the foundation pit is achieved. Compared with the traditional dewatering method, it reduces the construction steps, shortens the construction period, improves the quality of foundation construction, and achieves the benefits of reducing costs and increasing efficiency.

[0033] This patent also improves the blind pipe. By adopting the form of inner and outer pipes, it judges whether to grout the blind pipe by observing the grouting pressure and the calculated grouting volume during grouting, and whether the mobile pipe effectively blocks the staggered seepage holes and water-permeable holes, thereby effectively reducing the amount of seepage, and at the same time solving the problem of poor durability of the structure caused by it, extending the time to facilitate the operation of welding steel plates at the ends of the drainage pipes, and ensuring the quality of the sealing. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a top view of the overall structure of the present invention;

[0035] Figure 2 It is a vertical cross-sectional view of the overall structure of the present invention;

[0036] Figure 3 for Figure 2 A partial enlarged view of point A in the middle.

[0037] Figure 4 This is the construction structure drawing of the closed layer;

[0038] Figure 5 Schematic diagram of the internal structure of the blind tube;

[0039] Figure 6 It is a structural diagram of an elastic telescopic locking member. DETAILED DESCRIPTION

[0040] 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.

[0041] 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.

[0042] Example 1, as Figures 1 to 6 As shown, a local dynamic balance drainage construction method for a deep foundation pit is characterized by the following construction steps:

[0043] 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.

[0044] S200. After the foundation pit is excavated, drainage blind pipes 4 are installed around the bottom. The blind pipes 4 are 200 mm stainless steel pipes with water holes on all four sides. A movable pipe 41 is slidably installed inside the blind pipe 4. The movable pipe 41 is provided with water holes corresponding to the positions and equal in size to the water holes. One end of the movable pipe 41 is a blind head. The outside of the blind head is provided with an elastic telescopic locking member. The four blind pipes 4 are connected end to end and do not communicate with each other.

[0045] The drainage pipe 3 is connected to the blind pipe 4. A water pump 5 is installed at the outlet end of the drainage pipe 4. A float valve is set in the blind pipe 4 to control the start and stop of the water pump 5. When the water level in the blind pipe 4 rises to a certain height, the water pump 5 can start pumping water by controlling the float valve.

[0046] The number and installation location of the 5 water pumps are determined according to the seepage location and amount of the foundation pit bottom on site. An extra water pump 5 needs to be installed.

[0047] S300: Drain pipe 3 is connected from the foundation pit to an external sump 6. The pump 5 is located outside the foundation pit. 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 site requirements. After the drain pipe 3 exits the foundation pit, it is replaced with a water bag.

[0048] After the water pump 5 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 5 is started and stopped by the float valve to achieve dynamic balance of the water level.

[0049] 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;

[0050] 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;

[0051] 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.

[0052] 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;

[0053] 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;

[0054] 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;

[0055] During the construction process, it is necessary to continuously observe the groundwater level and the working condition of the water pump 5. If there is a failure of the water pump 5 or the amount of groundwater increases suddenly, start the standby water pump 5;

[0056] 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.

[0057] 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:

[0058] 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.

[0059] 2) First, stop the pump 5 to be blocked, and continue the operation of the other pumps 5. 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.

[0060] 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.

[0061] After observing the pressure of the grouting machine and calculating the amount of grouting liquid injected, it is determined that the bottom grouting is completed. After on-site inspection, the bottom grouting pressure is calculated to be area A. The pressurized grouting is continued until the grouting pressure reaches area B. At this time, the pressure is proportional to the locking pressure of the elastic telescopic locking member. Then, the seal of the drain pipe 3 is removed, and the grouting is continued until the grouting liquid overflows the drain pipe 3. The grouting is terminated.

[0062] 4) After the grouting is completed, the outlet of the drainage pipe 3 is sealed with a steel plate to ensure the welding quality and prevent water seepage, so as to ensure that there will be no groundwater seepage through the drainage pipe 3 in the later stage;

[0063] 5 And so on, the remaining drainage pipes 3 are grout-sealed.

[0064] Specifically, the drainage pipe 3 is provided with a water stop plate 31, which is fixed to 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. 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.

[0065] Specifically, 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 lifting device. 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 pressure-grouted 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.

[0066] Specifically, the elastic telescopic locking member includes a fixed tube 42, a movable rod and an elastomer. The fixed tube 42 is fixed to the inner side of the blind end of the blind tube 4, and the movable rod 43 rotates on the outer side of the blind head of the movable tube 41. The movable rod 43 partially extends into the fixed tube 42 and is connected to the fixed tube 42 through a spring. A guide groove 44 is provided on the fixed tube 42, and a unidirectional conduction structure is provided at the root of the guide groove 44. A guide pin 45 is fixedly installed on the movable rod 43, and the guide pin 45 and the guide groove 44 are slidably matched.

[0067] The one-way conduction structure includes a fixing seat 46 arranged on the outside of the fixing tube 42, and a spring and a wedge block 47 are provided in the fixing seat 46. The wedge block 47 is slidably installed in the fixing seat 46 through the spring, and a portion of the wedge block 47 extends to the outside of the guide groove 44 for one-way locking and fixing the guide pin 45.

[0068] Through preliminary on-site inspection and technicians' calculation, it is found that the approximate pressure range for bottom grouting is zone A. The appropriate elastic telescopic locking part specifications are selected based on the spring pressure value when the guide pin 4 is locked with the one-way conducting structure in the guide groove 44. When the pressure reaches zone A during grouting, the pressure and grouting volume continue to increase until the pressure is in zone B. The pressure in zone B is greater than the spring pressure value, and the grouting after reaching zone A will cause the movable pipe 41 to move axially relative to the blind pipe 4. The guide pin 45 moves along the guide groove 44, passes through the wedge block 47 and is locked and fixed to the root of the guide groove 44 by the wedge block 47. At this time, the seepage holes and the water-permeable holes are staggered, thereby achieving water seepage barrier, effectively extending the welding operation time of the pipe mouth steel plate of the drainage pipe 3 while ensuring the durability of the structure.

[0069] In summary, when the groundwater level is below the base elevation of the non-drop-slab area but above the base elevation of the deep foundation pit in the local drop-slab area, and drainage is required for local deep foundation pit construction, the drainage construction method proposed in this patent can be adopted. 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 foundation stability of the non-drop-slab area and the surrounding environment. This accumulates valuable construction experience for similar foundation pit drainage methods, and its results have important theoretical significance and engineering practical value.

[0070] 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 local dynamic balance drainage construction method for a deep foundation pit, 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. A movable pipe (41) is slidably installed inside the blind pipe (4). The movable pipe (41) is provided with water holes corresponding to the positions of the water holes and having the same size. One end of the movable pipe (41) is a blind head. An elastic telescopic locking member is provided on the outside of the blind head. The four blind pipes (4) are connected end to end and are not interconnected. The drainage pipe (3) and the blind pipe (4) are connected. A water pump (5) is installed at the outlet end of the drainage pipe (3). A float valve is provided in the blind pipe (4) to control the start and stop of the water pump (5). When the water level in the blind pipe (4) rises to a certain height, the water pump (5) can start pumping water by controlling the float valve. The number and installation location of the water pumps (5) are determined according to the seepage location and amount of seepage at the bottom of the foundation pit on site, and an additional reserved water pump (5) is required; S300, the drainage pipe (3) is connected from the foundation pit to the external water collection pit (6), the water pump (5) is located outside the foundation pit, 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 (5) 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 (5) 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 (5). If a water pump (5) fails or the amount of groundwater suddenly increases, the standby water pump (5) is started; 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; The elastic telescopic locking member comprises a fixed tube (42), a movable rod and an elastic body, wherein the fixed tube (42) is fixed to the inner side of the blind end of the blind tube (4), and the movable rod (43) rotates on the outer side of the blind head of the movable tube (41). The movable rod (43) partially extends into the fixed tube (42) and is connected to the fixed tube (42) via a spring. The fixed tube (42) is provided with a guide groove (44), and the root of the guide groove (44) is provided with a unidirectional conductive structure. A guide pin (45) is fixedly mounted on the movable rod (43), and the guide pin (45) and the guide groove (44) are slidably matched. The one-way conducting structure includes a fixing seat (46) arranged outside the fixing tube (42), a spring and a wedge block (47) are arranged in the fixing seat (46), the wedge block (47) is slidably installed in the fixing seat (46) via the spring, and a portion of the wedge block (47) extends to the outside of the guide groove (44) for one-way locking and fixing the guide pin (45).

2. A deep foundation pit local dynamic balance drainage construction method according to claim 1, 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 operation of the pump (5) to be blocked, and continue the operation of the other pumps (5). 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 calculating 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 drainage pipe (3) is sealed to ensure the welding quality and prevent water seepage, so as to ensure 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. A method for local dynamic balance drainage construction of a deep foundation pit 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 local dynamic balance drainage construction method for a deep foundation pit 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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