A system for actively controlling deformation of a foundation pit and a construction method thereof

Abstract

The present application relates to a kind of system and its construction method of actively controlling foundation pit deformation, which includes foundation pit retaining wall (1), grouting device (2), anti-lateral displacement pile (3) and barrier reinforcement (4), grouting device (2) is provided on the foundation pit retaining wall (1), the foundation pit retaining wall (1) is set to the outside of foundation pit, the barrier reinforcement (4) is set to the inside of foundation pit, the anti-lateral displacement pile (3) passes through barrier reinforcement (4), and is inserted into the soil layer in the lower part of barrier reinforcement (4);The barrier reinforcement (4) includes backrest reinforcement (41) and top sealing reinforcement (42), wherein the gap is left between backrest reinforcement (41) and foundation pit retaining wall (1), and top sealing reinforcement (42) is connected foundation pit retaining wall (1) and backrest reinforcement (41). Compared with prior art, the present application uses grouting technology to provide horizontal extrusion force for foundation pit retaining wall during foundation pit construction, and then actively controls wall horizontal deformation.

Description

Technical Field

[0001] This invention belongs to the field of civil engineering and foundation pit support engineering technology, and relates to a system for actively controlling foundation pit deformation and its construction method. Background Technology

[0002] With the development of urban underground space construction, the disturbance impact of deep foundation pit excavation on surrounding environmental facilities is becoming increasingly serious. Excessive deformation of the foundation pit retaining structure can lead to settlement and cracking of surrounding buildings, pipeline rupture, and road collapse, jeopardizing the safety of surrounding environmental facilities. In saturated soft soil areas, due to the adverse geological characteristics of the foundation soil, such as high water content, high compressibility, low bearing capacity, and strong rheological properties, controlling the deformation of foundation pits is even more difficult. The deformation pattern of the retaining wall of a deep foundation pit in soft soil often exhibits a parabolic shape, with the maximum horizontal deformation mostly occurring near the bottom of the pit, while the deformation at the top and bottom of the retaining wall is generally smaller than that in the middle. To control the deformation of the foundation pit retaining wall, conventional techniques mostly employ measures such as increasing the cross-section of the retaining wall, increasing the support stiffness, and adding cement-soil foundation reinforcement. Increasing the cross-section of the retaining wall can improve its flexural stiffness and reduce bending deformation; increasing the support stiffness can reduce the horizontal deformation of the wall above the pit bottom; and adding cement-soil foundation reinforcement can improve the mechanical properties of the soil below the pit bottom to a certain extent, allowing it to provide greater reaction force for the retaining wall below the pit bottom and constrain the horizontal deformation of the lower part of the retaining wall. However, engineering practice shows that the effect of cement-soil foundation reinforcement on controlling the deformation of the wall below the pit bottom is limited. First, the mass dispersion of the cement-soil reinforcement is large, and the reinforcement cannot form a reliable whole; second, as the scale of the foundation pit excavation increases, the volume of the cement-soil foundation reinforcement must also increase accordingly. When the reinforcement replacement rate is low, it cannot provide effective horizontal reaction force, and simply increasing the volume of the reinforcement will increase the project cost; third, cement-soil foundation reinforcement is a passive force-bearing measure, that is, the retaining wall must first undergo horizontal deformation to exert a squeezing effect on the reinforcement before the reinforcement can provide horizontal reaction force, which is also relatively unfavorable for deformation control.

[0003] Patent CN110093927A discloses a method for controlling the deformation of tunnels outside a foundation pit. It employs a rigid-flexible combined segmented barrier system design method, determining the design parameters of the barrier system based on the foundation pit excavation depth H, the net distance D between the tunnel and the foundation pit retaining structure, and the tunnel center burial depth S. The barrier system is divided into flexible and rigid sections, with reinforced concrete bored piles combined with sand piles as the main structure. Construction is carried out in upper and lower rigid-flexible segments, with the rigid section using reinforced concrete bored piles and the flexible section using sand piles. However, this patent involves setting up an isolation barrier outside the foundation pit retaining wall and grouting outside the foundation pit. The biggest drawback of this patent is that it occupies space outside the foundation pit. In densely populated urban areas where land is extremely valuable, most new projects make full use of the space, excavating foundation pits as close to the boundary line as possible. Therefore, most projects do not have the space outside the pit to implement the external isolation barrier and external grouting proposed in this patent. Furthermore, this patent only protects tunnels next to the foundation pit, resulting in a narrow scope of application. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects of the existing technology and provide a system and construction method for actively controlling the deformation of foundation pits. During the construction of foundation pits, this invention uses grouting technology to provide horizontal extrusion pressure to the retaining wall of the foundation pit, thereby actively controlling the horizontal deformation of the wall, improving the effect of soft soil foundation pit deformation control technology, and further improving the construction level of underground space.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] One of the technical solutions of the present invention is to provide a system for actively controlling the deformation of a foundation pit. The system includes a foundation pit retaining wall, a grouting device, anti-lateral displacement piles, and a barrier reinforcement body. The grouting device is installed on the foundation pit retaining wall, which is located on the outside of the foundation pit. The barrier reinforcement body is located on the inside of the foundation pit, and the anti-lateral displacement piles pass through the barrier reinforcement body and are inserted into the soil layer below the barrier reinforcement body.

[0007] Furthermore, the barrier reinforcement is made of cement-soil, including back reinforcement and capping reinforcement, wherein there is a gap between the back reinforcement and the foundation pit retaining wall, and the capping reinforcement connects the foundation pit retaining wall and the back reinforcement.

[0008] As a preferred technical solution, the depth of the top reinforcement is at least 1m less than the depth of the back reinforcement.

[0009] Furthermore, the grouting device includes a grouting machine, a grouting pipe, and a counter-pressure plate.

[0010] Furthermore, the grouting pipe includes a main pipe, a multi-port pipe, and branch vertical pipes that are interconnected. The main pipe is connected to the grouting machine. The branch vertical pipes are arranged along the outer wall of the foundation pit retaining wall inside the foundation pit and are inserted into the soil below the excavation surface from the ground down until they reach the gap between the foundation pit retaining wall and the reinforced enclosure. A flow control valve is installed at the front end of the branch vertical pipe.

[0011] Furthermore, the branch vertical pipe is fixed to the pit retaining wall by a support structure, and the support structure is provided with a restriction hole. The support structure is made of concrete beam, concrete slab or steel support.

[0012] Furthermore, the counter-pressure plate is made of wood, steel, or precast concrete and is placed above the capping reinforcement, and fixed to the pit retaining wall by corbels.

[0013] Furthermore, the anti-lateral displacement pile is a cast-in-place pile or a steel section, which passes through the back reinforcement and is inserted into the soil layer below the back reinforcement.

[0014] Furthermore, the retaining wall of the foundation pit is constructed using diaphragm walls, cast-in-place piles, or cement-soil mixing walls.

[0015] Furthermore, a monitoring device is installed on the retaining wall of the foundation pit. The monitoring device includes an inclinometer and an earth pressure gauge. The inclinometer is arranged inside the structure of the retaining wall, and the earth pressure gauge is installed on the outer wall of the retaining wall outside the foundation pit.

[0016] One of the technical solutions of the present invention is to provide a construction method for a system for actively controlling the deformation of a foundation pit, the construction method comprising the following steps:

[0017] (1) Set up an inclinometer inside the steel cage of the foundation pit retaining wall and set up an earth pressure gauge on the outer wall of the foundation pit retaining wall outside the foundation pit.

[0018] (2) Construct a barrier reinforcement and anti-lateral displacement piles inside the foundation pit;

[0019] (3) Set the early warning value S for the horizontal deformation of the foundation pit retaining wall;

[0020] (4) Excavation of the foundation pit: a supporting structure is constructed immediately after each layer of soil is excavated. During the excavation, the horizontal deformation of the foundation pit retaining wall is observed using an inclinometer, and the earth pressure P on the outer wall of the pit is obtained using an earth pressure gauge. w ;

[0021] (5) When the horizontal deformation of the foundation pit retaining wall reaches the warning value S, install the grouting device, install the grouting machine, main pipe, multi-way pipe and flow control valve on the ground outside the pit, install the branch vertical pipe along the outer wall of the foundation pit retaining wall on the inner side of the foundation pit, the branch vertical pipe passes through the limiting hole on the support structure and is inserted into the soil below the excavation surface until the gap between the foundation pit retaining wall and the rear reinforcement enclosure, install the counter pressure plate on the top reinforcement, and fix the counter pressure plate to the foundation pit retaining wall by the corbel;

[0022] (6) Start grouting, grouting pressure P z It should be greater than P w The grout is injected into the space enclosed by the foundation pit retaining wall and the barrier reinforcement. The grout exerts outward pressure on the foundation pit retaining wall, thereby reducing the horizontal deformation of the foundation pit retaining wall.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) Compared with traditional foundation pit support technology, which cannot actively control the horizontal deformation of the foundation pit retaining wall below the bottom of the pit, the present invention can use grouting technology to provide horizontal extrusion force to the foundation pit retaining wall during foundation pit construction, thereby actively controlling the horizontal deformation of the wall.

[0025] (2) When grout is injected directly into the soil, the grout will surge along the weak surface of the soft soil, or even directly emerge from the ground, resulting in pressure loss and the amount of grout injected is uncontrollable. This invention uses a barrier reinforcement to isolate the top and horizontal direction of the grouting area to prevent the grout from surging and flowing away.

[0026] (3) The combination of the rear reinforcement and anti-lateral displacement pile of the present invention enables the rear reinforcement to provide more stable rear support when subjected to the pressure of grouting slurry.

[0027] (4) The counter-pressure plate of the present invention is pressed on the top of the sealing reinforcement and fixed to the foundation pit retaining wall by the corbel. The counter-pressure plate can provide vertical restraint for the sealing reinforcement and can prevent the grout from lifting the sealing reinforcement and causing the grout to emerge from the soil surface.

[0028] (5) The grouting pressure of the present invention is greater than the soil pressure on the outer wall of the pit. The pressure on the inner side of the pit retaining wall exceeds the soil pressure on the outer side, which enables the pit retaining wall to generate a reverse displacement to the outside, thereby reducing the deformation of the pit.

[0029] (6) The present invention utilizes a multi-port pipe and a flow control valve, enabling the grouting machine to grout at multiple locations simultaneously, thereby improving the efficiency of a single grouting machine.

[0030] (7) Since the deformation at different locations of the foundation pit is uneven, the retaining wall of the foundation pit at different locations should be set with grouting pressure and grouting volume respectively. Each branch vertical pipe of the present invention is equipped with a flow control valve at the front end, so the grouting effect at different locations can be independently controlled, which improves the accuracy of control.

[0031] (8) The branch vertical pipe of the present invention passes through the support structure and uses the limiting hole to fix the branch vertical pipe and prevent the branch vertical pipe from shifting under the grouting pressure.

[0032] (9) All implementations of this invention are carried out inside the foundation pit, and no construction is required outside the foundation pit area, so it is more convenient to use;

[0033] (10) This invention does not limit the protected objects and has a wider range of applications. Attached Figure Description

[0034] Figure 1 This is a cross-sectional schematic diagram of the enclosure structure with actively controlled deformation in an embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram of the grouting device in an embodiment of the present invention.

[0036] Explanation of markings in the diagram:

[0037] 1—Pit retaining wall, 2—Grouting device, 21—Grouting machine, 22—Main pipe, 23—Multi-port pipe, 24—Flow control valve, 25—Branch vertical pipe, 26—Counter pressure plate, 3—Anti-lateral displacement pile, 4—Barrier reinforcement, 41—Back reinforcement, 42—Top reinforcement, 5—Support structure, 51—Limiting hole. Detailed Implementation

[0038] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0039] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0040] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0041] Example:

[0042] A system for actively controlling the deformation of foundation pits, such as Figure 1 As shown, the structure includes a retaining wall 1, a grouting device 2, anti-lateral displacement piles 3, a barrier reinforcement 4, and a supporting structure 5. The retaining wall 1 is equipped with the grouting device 2 and is located on the outside of the foundation pit. The retaining wall 1 can be a diaphragm wall, cast-in-place piles, or a cement-soil mixing wall; in this embodiment, a diaphragm wall is used. The barrier reinforcement 4 is a cement-soil reinforcement located inside the foundation pit, consisting of a backing reinforcement 41 and a capping reinforcement 42. A gap is left between the backing reinforcement 41 and the retaining wall 1. One end of the capping reinforcement 42 abuts against the retaining wall 1, and the other end connects to the backing reinforcement 41. The backing reinforcement 41 and the capping reinforcement 42 overlap to form a whole, with the depth of the capping reinforcement 42 being 1m less than the depth of the backing reinforcement 41. The anti-lateral displacement piles 3 can be cast-in-place piles or steel sections; in this embodiment, cast-in-place piles are used, located inside the foundation pit. The anti-lateral displacement pile 3 passes through the rear reinforcement 41 and is inserted into the soil layer below the rear reinforcement 41.

[0043] like Figure 2 As shown, the grouting device 2 includes a grouting machine 21, grouting pipes, and a counter-pressure plate 26. The grouting pipes include a main pipe 22, a multi-port pipe 23, and branch vertical pipes 25. The main pipe 22 is connected to the grouting machine 21. A flow control valve 24 is installed at the front end of the branch vertical pipes 25.

[0044] like Figure 1 As shown, the branch vertical pipe 25 is arranged along the outer wall of the pit retaining wall 1 inside the pit, inserting downwards from the ground into the soil below the excavation surface until it reaches the gap enclosed by the pit retaining wall 1 and the rear reinforcement 41. The counterweight plate 26 can be a wooden board, steel plate, or precast concrete slab. In this embodiment, a precast concrete slab is selected. The counterweight plate 26 is located above the capping reinforcement 42 and is fixed to the pit retaining wall 1 by a corbel. The branch vertical pipe 25 is fixed to the pit retaining wall 1 by a support structure 5. The support structure 5 can be a concrete beam, concrete slab, or steel support. In this embodiment, a concrete beam is selected. A limiting hole 51 is reserved on the support structure 5.

[0045] A monitoring device is installed on the retaining wall 1 of the foundation pit. The monitoring device includes an inclinometer and an earth pressure gauge. The inclinometer is arranged inside the structure of the retaining wall 1, and the earth pressure gauge is installed on the outer wall of the retaining wall 1 on the outer side of the foundation pit.

[0046] A construction method for a system for actively controlling the deformation of a foundation pit includes the following steps:

[0047] (1) Set up an inclinometer inside the steel cage of the foundation pit retaining wall 1, and set up an earth pressure gauge on the outer wall of the steel cage of the foundation pit retaining wall 1 located outside the foundation pit.

[0048] (2) Construct a barrier reinforcement 4 and anti-lateral displacement piles 3 inside the foundation pit;

[0049] (3) Set the early warning value S for the horizontal deformation of the foundation pit retaining wall;

[0050] (4) Excavation of the foundation pit: a support structure 5 is constructed immediately after each layer of soil is excavated. During the excavation, the horizontal deformation of the foundation pit retaining wall 1 is observed using an inclinometer, and the earth pressure P on the outer wall side of the pit is obtained using an earth pressure gauge. w ;

[0051] (5) When the horizontal deformation of the foundation pit retaining wall 1 reaches the warning value S, install the grouting device 2, install the grouting machine 21, main pipe 22, multi-port pipe 23 and flow control valve 24 on the ground outside the pit, install the branch vertical pipe 25 along the outer wall of the foundation pit retaining wall 1 located inside the foundation pit, the branch vertical pipe 25 passes through the limiting hole 51 on the support structure 5 and is inserted into the soil below the excavation surface until the gap enclosed by the foundation pit retaining wall 1 and the back reinforcement 41, install the counter pressure plate 26 on the top reinforcement 42, and fix the counter pressure plate 26 to the foundation pit retaining wall 1 by the corbel;

[0052] (6) Start grouting, grouting pressure P z It should be greater than P w The grout is injected into the space enclosed by the foundation pit retaining wall 1 and the barrier reinforcement 4. The grout exerts outward pressure on the foundation pit retaining wall 1, thereby reducing the horizontal deformation of the foundation pit retaining wall 1.

[0053] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A system for actively controlling the deformation of a foundation pit, characterized in that, The system includes a foundation pit retaining wall (1), a grouting device (2), anti-lateral displacement piles (3), and a barrier reinforcement body (4). The grouting device (2) is installed on the foundation pit retaining wall (1). The foundation pit retaining wall (1) is located on the outside of the foundation pit. The barrier reinforcement body (4) is located on the inside of the foundation pit. The anti-lateral displacement piles (3) pass through the barrier reinforcement body (4) and are inserted into the soil layer below the barrier reinforcement body (4). The barrier reinforcement (4) is made of cement soil and includes back reinforcement (41) and top reinforcement (42). There is a gap between the back reinforcement (41) and the foundation pit retaining wall (1). The top reinforcement (42) connects the foundation pit retaining wall (1) and the back reinforcement (41). The grouting device (2) includes a grouting machine (21), a grouting pipe and a counter-pressure plate (26). The grouting pipe includes a main pipe (22), a multi-port pipe (23), and branch vertical pipes (25) that are interconnected. The main pipe (22) is connected to the grouting machine (21). The branch vertical pipes (25) are arranged along the outer wall of the pit retaining wall (1) inside the pit and inserted into the gap between the pit retaining wall (1) and the back reinforcement (41). A flow control valve (24) is installed on the branch vertical pipes (25).

2. The system for actively controlling the deformation of a foundation pit according to claim 1, characterized in that, The branch vertical pipe (25) is fixed to the pit retaining wall (1) by the support structure (5). The support structure (5) has a reserved limiting hole (51). The support structure (5) is made of concrete beam, concrete slab or steel support.

3. The system for actively controlling the deformation of a foundation pit according to claim 1, characterized in that, The counter-pressure plate (26) is made of wood, steel or precast concrete and is placed above the capping reinforcement (42) and fixed to the pit retaining wall (1).

4. The system for actively controlling the deformation of a foundation pit according to claim 1, characterized in that, The anti-lateral displacement pile (3) is made of cast-in-place pile or steel section, passes through the back reinforcement (41), and is inserted into the soil layer below the back reinforcement (41).

5. The system for actively controlling the deformation of a foundation pit according to claim 1, characterized in that, The foundation pit retaining wall (1) is made of underground continuous wall, cast-in-place pile or cement-soil mixing wall.

6. The system for actively controlling the deformation of a foundation pit according to claim 1, characterized in that, A monitoring device is installed on the foundation pit retaining wall (1). The monitoring device includes an inclinometer and an earth pressure gauge. The inclinometer is arranged inside the structure of the foundation pit retaining wall (1), and the earth pressure gauge is installed on the outer wall of the foundation pit retaining wall (1) located outside the foundation pit.

7. A construction method for a system for actively controlling the deformation of a foundation pit as described in any one of claims 1 to 6, characterized in that, The construction method includes the following steps: (1) Set up an inclinometer inside the steel cage of the retaining wall (1) of the foundation pit, and set up an earth pressure gauge on the outer wall of the retaining wall (1) of the foundation pit outside the foundation pit. (2) Construct a barrier reinforcement (4) and anti-lateral displacement piles (3) inside the foundation pit; (3) Set the horizontal deformation warning value of the foundation pit retaining wall (1); (4) Excavation of the foundation pit: a support structure shall be constructed immediately after each layer of earth is excavated (5). (5) When the horizontal deformation of the foundation pit retaining wall (1) reaches the warning value, install the grouting device (2), install the grouting machine (21), main pipe (22), multi-port pipe (23) and flow control valve (24) on the ground outside the pit, install the branch vertical pipe (25) along the outer wall of the foundation pit retaining wall (1) located inside the foundation pit, the branch vertical pipe (25) passes through the limiting hole (51) on the support structure (5) and is inserted into the soil below the excavation surface until the gap between the foundation pit retaining wall (1) and the back reinforcement (41) is enclosed, install the counter pressure plate (26) on the top reinforcement (42), and fix the counter pressure plate (26) on the foundation pit retaining wall (1); (6) Start grouting and inject grout into the space enclosed by the foundation pit retaining wall (1) and the barrier reinforcement body (4).

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