阅读说明：本技术 零位移基坑工程施工方法及其所用的基坑支护结构 (Zero-displacement foundation pit engineering construction method and foundation pit supporting structure used by same ) 是由 张继红 于 2020-08-03 设计创作，主要内容包括：本发明涉及土木工程领域,特别是涉及基坑支护工程领域中的一种零位移基坑工程施工方法及所用的基坑支护结构,该方法主要包括以下步骤：b)在挡土构件(6)与被保护对象(4)之间置入袋子(2)；c)在袋子(2)内盛装流体(3)；d)通过袋子(2)内的流体(3)对袋子(2)外侧的土体施加应力,补偿因基坑(5)施工产生的应力损失；e)通过被保护对象(4)一侧土体应力损失的补偿,控制被保护对象(4)的位移,本发明可对被保护对象(4)的位移进行实时控制,可减消基坑(5)施工影响,且施工造价低,质量可控,安全度、可靠度高。(The invention relates to the field of civil engineering, in particular to a zero-displacement foundation pit engineering construction method and a used foundation pit supporting structure in the field of foundation pit supporting engineering, and the method mainly comprises the following steps: b) placing the bag (2) between the retaining member (6) and the object (4) to be protected; c) the bag (2) is filled with fluid (3); d) applying stress to soil on the outer side of the bag (2) through the fluid (3) in the bag (2) to compensate the stress loss generated by the construction of the foundation pit (5); e) the invention can control the displacement of the protected object (4) in real time by compensating the stress loss of the soil body on one side of the protected object (4), can reduce the construction influence of the foundation pit (5), and has the advantages of low construction cost, controllable quality, high safety and reliability.)

1. A construction method of zero displacement foundation pit engineering comprises the following steps:

a) determining the positions of the excavation surface of the foundation pit (5) and the protected object (4);

b) a bag (2) with the function of containing fluid is arranged between the excavation surface of the foundation pit (5) and the protected object (4);

c) the bag (2) is filled with fluid (3);

d) applying stress to soil on the outer side of the bag (2) through the fluid (3) in the bag (2) to compensate the stress loss of the soil on one side of the protected object (4) caused by the construction of the foundation pit (5);

e) the displacement of the protected object (4) is controlled by compensating the stress loss of the soil body on one side of the protected object (4).

2. The construction method of zero displacement foundation pit engineering according to claim 1, wherein the fluid (3) in the steps b), c) and d) is one or more of liquid, gas or colloid.

3. The construction method of zero displacement foundation pit according to claim 1, wherein in step b), one or two or more bags (2) with the same or different depths of penetration are arranged between the excavation surface of the foundation pit (5) and the protected object (4).

4. A zero displacement foundation pit engineering construction method according to claim 1, characterized in that in step b) one or two or more bags (2) are arranged at different depths in the same plane.

5. The construction method of zero displacement foundation pit according to claim 1, wherein in the step b), one or two or more bags (2) are provided and the bags (2) are communicated with the ground surface.

6. A method as claimed in claim 1, wherein in step c) the bag (2) is filled with solids.

7. A method according to claim 1, wherein in step c) the bags (2) are filled with granular solids, and the granular solids are filled into the bags (2) with a desired consistency by one or a combination of gravity, vibration or fluid flow.

8. The construction method of zero displacement foundation pit according to claim 1, wherein in step d), the bag (2) is sealed and filled with liquid or gas, and the stress is added to the soil outside the bag by pressurizing the gas or liquid in the bag (2).

9. The construction method of zero displacement foundation pit engineering according to claim 1, wherein in the step d), the magnitude and distribution of the stress applied to the soil outside the bag (2) is adjusted in real time by adjusting the pressure of the fluid in the bag (2) in real time, and the stress applied to the soil outside the bag (2) is not less than or less than the stress loss caused by the construction of the foundation pit (5) locally or completely.

10. The construction method of a zero displacement foundation pit according to claim 1, wherein the construction of the foundation pit (5) in the step d) is one or a combination of two or more of the construction of a foundation pit enclosure structure, the construction of foundation pit excavation, the construction of foundation pit support replacement, the construction of foundation pit dewatering, the construction of an underground structure and the construction of foundation pit backfill.

11. A foundation pit supporting structure used in the zero displacement foundation pit engineering construction method according to claim 1, characterized by comprising five parts of a soil retaining member (6), an inner support (7), a bag (2), a fluid (3) and a fluid pressure control device (8), wherein the soil retaining member (6) is a supporting and blocking type structural vertical member which is arranged on the side wall of the foundation pit and embedded in the bottom surface of the foundation pit, the inner support (7) is a structural component which is arranged in the foundation pit and is composed of reinforced concrete or steel members and used for supporting the soil retaining member (6), the bag (2) is a flexible component with a fluid containing function, the bag (2) is positioned between the soil retaining member (6) and the soil body outside the soil retaining member (6) or in the soil body outside the excavation surface of the foundation pit, the fluid (3) is one or a combination of a plurality of gases, liquids or colloids with flowing performance, the fluid (3) is contained in the bag (2), the fluid pressure control device (8) is a device with the function of adjusting the fluid pressure contained in the bag (2), and the fluid pressure control device (8) is connected with the bag (2).

12. A construction method of zero displacement foundation pit engineering comprises the following steps:

a) determining the positions of the excavation surface of the foundation pit (5) and the protected object (4);

b) constructing a steel pipe pile (9) on the side wall of the foundation pit to serve as a soil retaining member, and arranging a bag (2) with a fluid containing function on the outer surface of one side, close to a protected object (4), of the steel pipe pile (9);

c) the bag (2) is filled with fluid (3), and a fluid pressure control device (8) is arranged to form a foundation pit soil retaining device;

d) applying stress to soil on the outer side of the bag (2) through the fluid (3) in the bag (2) to compensate the stress loss of the soil on one side of the protected object (4) caused by the construction of the foundation pit (5);

e) the displacement of the protected object (4) is controlled by compensating the stress loss of the soil body on one side of the protected object (4).

f) And after the foundation pit is backfilled, reducing the frictional resistance of the outer surface of the steel pipe pile (9) through the bag (2), and pulling out the steel pipe pile (9).

13. The method as claimed in claim 12, wherein in the step b), the double or multi-layered bag (2) is formed on the outer surface of the steel pipe pile (9).

14. The method as claimed in claim 12, wherein in step f), the pile pulling resistance is reduced by applying a lubricant to the outer surface of the steel pipe pile (9) and between the bags (2), or by providing two or more layers of the bags (2), or by using the fluid (3) in the bags (2).

15. The construction method of zero displacement foundation pit according to claim 12, wherein in step f), the steel pipe pile (9) is pulled out by earth plug compensation.

16. A soil retaining device for the construction method of zero displacement foundation pit according to claim 12, characterized in that the soil retaining device comprises four parts, namely a steel pipe pile (9), a bag (2), a fluid (3) and a bag connector (10), wherein the steel pipe pile (9) is a soil retaining member in foundation pit support, the bag (2) is a flexible component with a function of containing the fluid, the bag (2) is located at an outer surface position of the steel pipe pile (9), the bag (2) is a component with a function of providing positive pressure between the steel pipe pile (9) and a soil body, the fluid (3) is one or a combination of several of gas, liquid or colloid with fluidity contained in the bag (2), the bag connector (10) is a component for firmly connecting the bag (2) and the steel pipe pile (9), and the bag connector (10) is located near the bottom of the bag (2).

17. A soil retaining device according to claim 16, wherein the bag (2) is a flexible member having a property of gradually separating from the bottom to the top when the steel pipe pile (9) is pulled out.

18. A soil retaining device according to claim 16, wherein a lubricant having a function of reducing friction is provided between the bag (2) and the outer surface of the steel pipe pile (9).

19. Soil retaining device according to claim 16, characterized in that the said bag (2) is a bag placed in two or more superimposed layers.

Technical Field

The invention relates to the field of foundation pit supporting engineering in the field of civil engineering.

Background

The development of underground space by excavation of foundation pit is the most applied construction form of underground engineering, the construction of subway stations in subway tunnel engineering is usually realized by excavation of foundation pit, and the construction of other underground engineering such as pipe jacking and the like also relates to foundation pit construction engineering. In the foundation pit construction and enclosure engineering, a large number of buildings (structures) needing protection, such as built buildings, underground pipelines, subway tunnels and the like, are often encountered near the foundation pit. Especially, when a house, a subway line, a high-speed rail line and magnetic suspension are distributed near a foundation pit, the protection requirement is very high, and when a precise equipment instrument is met, the harsh protection requirement of zero displacement is sometimes provided. At present, the main technical means for solving the problems is to greatly enhance the strength and rigidity of the foundation pit enclosure structure, so that the construction cost of the foundation pit enclosure construction is very high. The foundation pit enclosure system provides bearing capacity through deformation, so that deformation and displacement of the protected object are still inevitable in the foundation pit construction process no matter how much cost is added on the foundation pit enclosure. In recent years, in a section where deformation control of a protected object is very strict, a servo system has been used to reduce deformation caused by foundation pit construction. However, the biggest problem of the servo system is that concentrated force can only be applied to a supporting position, loading is difficult to be carried out near or below an excavation surface, and loading cannot be carried out before supporting construction and under working conditions of support removal, support replacement, precipitation and the like. The deformation control capability of the protected object is limited. Moreover, for a large amount of used reinforced concrete building envelopes and supporting systems, great deformation is also generated along with the construction and concrete curing period, which are difficult problems which cannot be solved by the prior art.

Disclosure of Invention

The first purpose of the invention is to provide a zero-displacement foundation pit engineering construction method, which applies distributed stress in a soil body, controls the displacement (including horizontal displacement and vertical displacement) of a protected object accompanied by the foundation pit construction process in real time, releases the soil body stress accompanied by the foundation pit construction in real time for compensation, and can eliminate the influence of the foundation pit engineering construction on the protected object.

The first zero-displacement foundation pit engineering construction method comprises the following steps:

a) determining the positions of a foundation pit excavation surface and a protected object;

b) placing a bag with a fluid containing function between the excavation surface of the foundation pit and the protected object;

c) containing a fluid in the bag;

d) applying stress to the soil body outside the bag through the fluid in the bag to compensate the stress loss of the soil body on one side of the protected object caused by the construction of the foundation pit engineering;

e) and controlling the displacement of the protected object by compensating the stress loss of the soil body on one side of the protected object.

In the first zero-displacement foundation pit engineering construction method, the fluid in the step b), the step c) and the step d) may be one or a combination of several of liquid, gas or colloid.

In the first zero-displacement foundation pit engineering construction method, one or more bags with the same or different soil penetration depths may be arranged between the excavation surface of the foundation pit and the protected object in the step b).

In the first zero-displacement foundation pit engineering construction method, one or two or more bags may be arranged at different depths in the same plane position in the step b).

In the first zero-displacement foundation pit construction method, one or two or more bags may be provided in the step b) and the bags may be communicated with the ground surface.

In the first zero-displacement excavation construction method, the bag may be filled with a solid in the step c).

In the first zero-displacement foundation pit construction method, in the step c), the granular solid may be filled in the bag, and the granular solid may be filled in the bag with a required compactness by one or a combination of gravity, vibration or fluid flow.

In the first zero displacement foundation pit construction method, in the step d), the bag is sealed and filled with the fluid, and the fluid in the bag is pressurized to apply stress to the soil outside the bag.

In the first zero-displacement foundation pit engineering construction method, in the step d), the magnitude and distribution of the stress applied to the soil body outside the bag can be adjusted in real time by adjusting the pressure of the fluid in the bag in real time, and the stress applied to the soil body outside the bag is not less than or less than the stress loss generated by foundation pit construction locally or completely.

In the first construction method of the zero-displacement foundation pit, the foundation pit construction in the step d) is one or a combination of more of foundation pit support structure construction, foundation pit excavation construction, foundation pit support replacement construction, foundation pit dewatering construction, underground structure construction and foundation pit backfill construction.

In the first zero-displacement foundation pit engineering construction method, in the step d), the magnitude and distribution of stress applied to the soil mass outside the bag can be adjusted in real time by adjusting the pressure intensity of the fluid in the bag in real time according to different working conditions and time of foundation pit construction.

The second purpose of the invention is to provide a foundation pit supporting structure used in the first zero-displacement foundation pit engineering construction method, which can smoothly realize the first zero-displacement foundation pit engineering construction method and has high safety, high construction speed and low construction cost.

The foundation pit supporting structure comprises five parts, namely a soil retaining member, an inner support, a bag, fluid and a fluid pressure control device, wherein the soil retaining member is a retaining type structural vertical member which is arranged on the side wall of a foundation pit and embedded into the bottom surface of the foundation pit, the inner support is a structural component which is arranged in the foundation pit and is composed of reinforced concrete or steel members and used for supporting the soil retaining member, the bag is a flexible component with a fluid containing function, the bag is positioned between the soil retaining member and the soil body on the outer side of the soil retaining member or in the soil body on the outer side of an excavation surface of the foundation pit, the fluid is one or a combination of a plurality of gases, liquids or colloids with flowing performance, the fluid is contained in the bag, the fluid pressure control device is a device with a function of adjusting the fluid pressure contained in the bag, and the fluid pressure control.

The third purpose of the invention is to provide a second zero-displacement foundation pit engineering construction method, which combines a soil retaining member with bagged fluid, controls the displacement (including horizontal displacement and vertical displacement) of a protected object in real time in the foundation pit construction process by applying distributed stress in the soil body, compensates the soil body stress release in real time in the foundation pit construction process, and can reduce the influence of the foundation pit engineering construction on the protected object.

The second zero-displacement foundation pit engineering construction method comprises the following steps:

a) determining the positions of a foundation pit excavation surface and a protected object;

b) constructing a steel pipe pile on the side wall of the foundation pit to serve as a soil retaining member, and arranging a bag with a fluid containing function on the outer surface of one side, adjacent to a protected object, of the steel pipe pile;

c) filling fluid in the bag, and installing a fluid pressure control device to form a foundation pit soil retaining device;

d) applying stress to the soil body outside the bag through the fluid in the bag to compensate the stress loss of the soil body on one side of the protected object caused by foundation pit construction;

e) and controlling the displacement of the protected object by compensating the stress loss of the soil body on one side of the protected object.

f) And after the foundation pit is backfilled, reducing the frictional resistance of the outer surface of the steel pipe pile through the bag, and pulling out the steel pipe pile.

In the second zero-displacement foundation pit construction method, in the step b), a double-layer or multi-layer bag may be provided on the outer surface of the steel pipe pile.

In the second zero-displacement foundation pit construction method, in the step f), the pile pulling resistance may be reduced by applying a lubricant to the outer surface of the steel pipe pile or between the bags, by providing two or more layers of multi-layered bags, or by using a fluid in the bags.

In the second zero-displacement foundation pit engineering construction method, in the step f), the steel pipe pile may be pulled out by using a soil plug compensation method.

The fourth object of the present invention is to provide a soil guard device for use in the second zero displacement foundation pit engineering construction method, which can smoothly implement the second zero displacement foundation pit engineering construction method of the present invention, can be fully recycled or partially recycled, and has a low cost.

The soil retaining device comprises a steel pipe pile, a bag, fluid and a bag connection part, wherein the steel pipe pile is a soil retaining component in foundation pit support, the bag is a flexible part with a fluid containing function, the bag is located on the outer surface of the steel pipe pile, the bag is a part with a function of providing positive pressure between the steel pipe pile and a soil body and reducing friction force, the fluid is one or a combination of a plurality of gases, liquids or colloids with flowing performance contained in the bag, the bag connection part is a part for firmly connecting the bag and the steel pipe pile, and the bag connection part is located near the bottom of the bag.

In the soil guard device, the bag is a flexible member having an ability to gradually come off the soil from the bottom toward the top when the steel pipe pile is pulled out.

In the soil guard device, a lubricant having a function of reducing friction is provided between the bag and the outer surface of the steel pipe pile.

In the soil retaining device, the bag is formed by two or more layers of bags stacked one on another.

The zero displacement foundation pit engineering construction method and the foundation pit supporting structure thereof take the general balance of the soil stress in a certain range outside the foundation pit as a starting point, can achieve the real-time control of the soil on one side of the protected object and the displacement of the protected object by controlling the stress boundary condition of the soil, can reduce and eliminate the influence of the foundation pit construction on the protected object, and aims to realize the zero displacement foundation pit construction, so that the existing building protection technology of the civil engineering under the foundation pit construction condition reaches the best, and the construction cost is low, the quality is controllable, and the safety and the reliability are high.

Drawings

Fig. 1 is a schematic plan view of a first isolation region layout for a first embodiment of the present invention;

fig. 2 is a schematic plan view of a second isolation region layout for use in the first embodiment of the present invention;

fig. 3 is a plan view of a third isolation region used in the first embodiment of the present invention;

FIG. 4 is a schematic cross-sectional view of a retaining structure of a foundation pit used in a zero-displacement foundation pit engineering construction method according to a first embodiment of the present invention;

FIG. 5 is a schematic cross-sectional view of a soil guard for a zero displacement pit engineering method according to a second embodiment of the present invention;

fig. 6 is a schematic cross-sectional view illustrating a soil guard for use in a zero displacement pit engineering method according to a second embodiment of the present invention.

Detailed Description

As a first embodiment of the present invention, the principle and implementation method of the first zero-displacement foundation pit engineering construction method of the present invention and a foundation pit supporting structure used thereby will be described with reference to fig. 1 to 4. First, a specific embodiment of the first zero-displacement foundation pit engineering construction method of the present invention is described. In the first step of the embodiment, the positions of the excavation surface of the foundation pit (5) and the protected object (4) are determined. For the convenience of expression, an isolation area (1) is divided between the excavation surface of the foundation pit (5) and the protected object (4). In the step, the distribution of different protected objects (4) and the relative position relation between the protected objects and the foundation pit (5) are fully known, and the isolation area (1) is divided according to different displacement control requirements. For example, for a linear protected object (4) such as a subway, a high-speed rail, a magnetic levitation, a raw water pipe, etc., the isolation area (1) may be defined along one side of the foundation pit (5) adjacent to the linear protected object (4) and appropriately extended at both sides of the foundation pit (5) approximately perpendicular to the linear protected object (4), as shown in fig. 1. In this step, if the protected object (4) is a building with a limited length such as a house, an isolation area (1) can be defined on the side of the foundation pit (5) adjacent to the protected object (4) and appropriately extended at both ends, as shown in fig. 2. In this step, if the protected object (4) is a point-shaped building and the occupied area is small, if the protected object (4) is a cultural relic such as a ancient tower, an isolation area (1) can be arranged around the protected object (4) under the condition of permission of land use, as shown in fig. 3. The main purpose of the step is to enable the position and the range of the isolation region (1) to be adaptive to the position of the protected object (4) and the protected requirement, establish a model, perform calculation analysis through a finite element method or by utilizing an elastoplasticity mechanics calculation theory, establish a reasonable isolation region (1), enable subsequent work to be economical, feasible and efficient, and meet the displacement control requirement of the protected object (4). The first step of this embodiment is completed and the process proceeds to the second step. In the step, a bag (2) with the function of containing fluid is arranged in the soil body of the isolation area (1). Because the bag (2) is of an elastic structure and can not contain the fluid (3) before being placed, the bag is small in size before being placed into a soil body and is easy to place. The bag (2) can be placed into the soil body by one or a combination of a static method, a hammering method and a vibration method. For example, the bag (2) may be temporarily fixed to a strip structure which is inserted into the soil mass while the bag (2) is inserted into the soil mass. The strip-shaped structure can be recycled. The bag (2) has the function of containing the fluid (3), and in order to improve the effect, the bag (2) has a better function of bearing certain pressure. In the step, holes can be drilled in the soil body, and the bag (2) is folded and placed into the soil body. In the step, one or more bags (2) with the same or different soil penetration depth can be arranged in the isolation area (1). The depth and the size of each bag (2) can be determined through calculation analysis or empirical judgment according to the excavation depth and the size of the foundation pit (5), the structural form of the enclosure of the foundation pit (5) and the displacement control requirement of the protected object (4). In the step, one or more bags (2) can be arranged at the same plane position and different depths, and the bags (2) are communicated with the ground. The main purpose is to provide more displacement control operation segments. Thereby completing the second step of this embodiment and proceeding to the third step. The main operation of the step is to contain the fluid (3) in the bag (2). The method for realizing the step is that the fluid (3) is directly filled through the communicating port between the bag (2) and the ground. The injected fluid (3) can be one or a combination of gases, liquids or colloids. In practice it may be water, air or slurry, etc. In this step, the bag (2) can be filled with solid or granular solid to reduce the dosage of the fluid (3) and prevent the displacement mutation which can be generated by the loss of the fluid (3) to ensure the safety of the control process. The third step of the embodiment is completed, and the fourth step is entered. The method comprises the following steps of applying stress to the soil body on the outer side of the bag (2) through the fluid (3) in the bag (2) and compensating the stress loss of the soil body on one side of the protected object (4) due to the construction of the foundation pit (5). According to the Pascal law, because the fluid (3) is filled in the bag (2) and the bag (2) is elastic, the fluid pressure stress in the bag (2) is transferred to the soil body outside the bag (2). In the excavation process of the foundation pit (5), stress release of an in-situ soil body can be generated in soil body excavation, the stress loss of the soil body on one side of the protected object (4) is compensated through the fluid (3) of the bag (2), and meanwhile, the reaction force of the compensated stress is transmitted to the enclosure structure of the foundation pit (5). In this step, the bag (2) may be sealed and filled with a liquid or gas, and the soil outside the bag (2) is stressed by pressurizing the gas or liquid inside the bag (2). In the step, the stress applied to the soil body outside the bag (2) can be partially or totally more than or less than the stress loss generated by the construction of the foundation pit (5), and the displacement of the protected object (4) is controlled by the superposition effect of stress compensation. In the step, the magnitude and the distribution of stress applied to the soil body on the outer side of the bag (2) can be adjusted in real time by adjusting the pressure of the fluid (3) in the bag (2) in real time according to different working conditions and time of excavation of the foundation pit (5). The fourth step of the present embodiment is completed, and the fifth step is entered. In the step, the displacement of the protected object (4) is controlled by compensating the stress loss of the soil body on one side of the protected object (4). In the step, the stress state of the soil body of the isolation area (1) between the protected object (4) and the foundation pit (5) is adjusted, so that the stability of the stress boundary condition of the soil body in the isolation area (1) is generally maintained, and the displacement of the protected object (4) is controlled. In the concrete implementation, the zero displacement target of the protected object (4) in the excavation process of the foundation pit (5) can be realized by the calculation means such as a finite element method and the like, the arrangement of the isolation region (1), the distribution, the quantity and the depth of the bags (2) and the real-time regulation and control of the pressure of the fluid (3) in the bags (2). In the implementation process, the precision of a calculation means is improved by combining with an observation result, and the expected displacement control target is finally met. The fluid (3) in this embodiment may be one or a combination of liquids, gases, and colloids, and may have a flowing property, for example, slurry may be used as the fluid (3). In this embodiment, the foundation pit construction is one or a combination of several of foundation pit support structure construction, foundation pit excavation construction, foundation pit support replacement construction, foundation pit dewatering construction, underground structure construction, and foundation pit backfill construction. The following section of this embodiment will mainly describe the supporting structure of the foundation pit used in this embodiment. The zero-displacement foundation pit engineering construction method introduced in this embodiment may adopt a foundation pit supporting structure as shown in fig. 4, where the foundation pit supporting structure includes five parts, namely, a soil-blocking member (6), an inner support (7), a bag (2), a fluid (3), and a fluid pressure control device (8), where the soil-blocking member (6) is a vertical member of a retaining structure that is disposed on a side wall of a foundation pit and embedded in a bottom surface of the foundation pit, and may be a vertical steel structure or a reinforced concrete structure, such as a cast-in-situ bored pile, an underground continuous wall, a pile of an SMW method, a steel pipe pile, a prefabricated reinforced concrete pile, and the. The inner support (7) is a structural component which is arranged in the foundation pit and is composed of reinforced concrete or steel components and used for supporting the soil retaining component (6), and when the inner support (7) is long, a vertical upright post is arranged in the foundation pit to ensure the vertical stability of the inner support (7). The bag (2) is a flexible part with a fluid containing function, the bag (2) is positioned between the soil retaining member (6) and soil on the outer side of the soil retaining member or in soil on the outer side of an excavation surface of a foundation pit, the fluid (3) is one or a combination of a plurality of gas, liquid or colloid with fluidity, the fluid (3) is contained in the bag (2), the fluid pressure control device (8) is a device with a function of adjusting the fluid pressure contained in the bag (2), the fluid pressure control device (8) is connected with the bag (2), and the fluid pressure control device (8) can be a combination of a fluid input device such as a water pump and a water pipe or a combination of a water tower and the water pipe. In the zero displacement foundation pit engineering, the load required to be considered in the design of a foundation pit supporting structure is larger than the load value selected by the design of a normal foundation pit, and the self-weight load of a soil body can be selected as the soil pressure acting on the soil retaining member (6). The effect of the fluid pressure in the bag (2) is preferably approximately equivalent to the static soil pressure and is preferably not greater than the passive soil pressure. The displacement control caused by the excavation of the foundation pit is controlled in real time, the soil body is difficult to recover once the displacement is generated, the displacement caused by the excavation of the foundation pit can be effectively controlled by controlling the fluid pressure in the bag (2) in real time in the whole process, and the ideal control target of the zero displacement of the foundation pit engineering can be realized by accurate regulation and strict construction operation.

As a second embodiment of the present invention, a second zero-displacement foundation pit construction method and a soil retaining device used in the method are described with reference to fig. 5 and 6. The second zero-displacement foundation pit construction method is similar to the first embodiment, and is different from the first embodiment in that a steel pipe pile (9) is adopted as a soil retaining member (6), and a bag (2) with a function of containing fluid (3) is arranged on the soil facing outer surface (13) of the side, close to a protected object, of the steel pipe pile (9). The outer surface of the steel pipe pile (9) can be provided with double-layer or multi-layer bags (2). After the foundation pit is backfilled, the frictional resistance of the outer surface of the steel pipe pile (9) is reduced through the bag (2), the steel pipe pile (9) is pulled out, and the steel pipe pile is recycled. The friction resistance of the outer surface of the steel pipe pile (9) when the steel pipe pile (9) is pulled out can be reduced by coating a lubricant on the outer surface of the steel pipe pile (9), or between each layer of bags (2), or by arranging two or more layers of bags (2), or by using the fluid (3) in the bags (2). In the steel pipe pile (9) pulling-out construction, the steel pipe pile (9) can be pulled out by adopting a soil plug compensation method, so that the influence of the pulled pile with soil is reduced. The following part of this embodiment, with reference to fig. 5 and 6, describes a soil guard device used in the second zero displacement foundation pit engineering construction method, the soil retaining device comprises four parts of a steel pipe pile (9), a bag (2), fluid (3) and a bag connection part (10), the steel pipe pile (9) is a soil retaining component (6) in foundation pit support, the bag (2) is a flexible part with a fluid containing function, the bag (2) is located on the outer surface of the steel pipe pile (9), the bag (2) is a part with functions of providing positive pressure between the steel pipe pile (9) and a soil body and reducing friction force, the fluid (3) is one or a combination of a plurality of gases, liquids or colloids with flowing performance and contained in the bag (2), the bag connection (10) is a part for firmly connecting the bag (2) and the steel pipe pile (9), and the bag connection (10) is located near the bottom of the bag (2). In this embodiment, the bag (2) may be a flexible member having a function of gradually separating from the bottom to the top when the steel pipe pile (9) is pulled out. The bag (2) is firmly connected with the steel pipe pile (9), and the construction of the bag (2) can be completed while the steel pipe pile (9) is placed. The bag (2) can be arranged only on the outer side of the excavation surface (11) of the foundation pit as shown in fig. 5 and 6, namely the position of the outer surface (13) of the steel pipe pile facing the soil, and if necessary, the bag (2) can be arranged on the outer surface (12) of the back soil of the steel pipe pile (9) positioned on the inner side of the excavation surface (11) of the foundation pit below the bottom surface of the foundation pit.

This patent includes, but is not limited to, other construction methods that may be substituted by those skilled in the art.