Design Method of Cantilever Rigid Retaining Structure for Sand Foundation Pit under Non-Limit State

Abstract

The present invention discloses a cantilever rigid retaining structure and design method for a sand foundation pit under a non-limit state, comprising the following steps: (1) determining the profile parameters of the foundation pit retaining structure and the physical and mechanical parameters of the soil; (2) determining the inclination angle of the active side sliding crack surface of the foundation pit and the allowable displacement of the top of the retaining structure; (3) calculating the friction angle at a distance z from the ground under a non-limit state based on the relationship between the friction angle and the horizontal displacement of the retaining wall; (4) calculating the active side earth pressure based on the oblique differential unit method, and calculating the passive side earth pressure using the Coulomb theory; (5) calculating the maximum bending moment and maximum shear force of the retaining structure, and determining the material and reinforcement of the retaining structure according to the maximum bending moment and the maximum shear force, and taking the final design result after verification. The present invention overcomes the defect that the non-limit state of the soil cannot be considered in the classical foundation pit design method, and can provide more accurate and reasonable guidance for the design and calculation of the retaining structure. The calculation method is simple and feasible, and has the value of popularization and application.

Description

Technical Field

[0001] The invention discloses a design method for a cantilever rigid retaining structure of a sand foundation pit under a non-limit state, and belongs to the technical field of geotechnical engineering. Background Art

[0002] With the rapid development of underground space development and construction in my country, the number of newly built foundation pits has increased accordingly. The existing retaining structure design methods are often designed based on the classical limit state earth pressure theory. However, in actual projects, due to the large stiffness of the retaining structure and the small deformation of the retaining structure, the rear soil is often in a state between the static state and the limit state, which is called the non-limit state.

[0003] At present, the design method of cantilever foundation pit retaining structure stipulated in the current Technical Code for Building Foundation Pit Support (JGJ 120-2012) is still based on the classical earth pressure theory. However, the actual situation that the active earth pressure on the retaining structure is too large and the passive earth pressure is too small is not considered, resulting in increased engineering risks on the active side during structural design and waste of construction costs on the passive side. During the construction process, the allowable displacement of the retaining structure required by the code is small, and the soil on both sides is mostly in a non-limit state. The classical earth pressure theory in the code cannot calculate the earth pressure on the retaining structure under this state.

[0004] To sum up, considering the actual situation of the project, it is a technical issue with great engineering application value to reasonably calculate the earth pressure on the cantilever rigid retaining structure of the sandy soil layer under non-limit state, so as to reasonably design the retaining structure, save investment and construction volume, and prevent engineering risks. Summary of the invention

[0005] The purpose of the present invention is to provide a design calculation method for a cantilever rigid retaining structure of a foundation pit in a sandy soil stratum under a non-limit state in response to the problems existing in the above-mentioned prior art, which can provide a design reference for the design of a cantilever rigid retaining structure of a foundation pit in a sandy soil stratum under a non-limit state.

[0006] To achieve the above object, the technical solution of the present invention is:

[0007] In a first aspect, the present invention provides a method for designing a cantilever rigid retaining structure for a sand foundation pit under a non-limit state, the method comprising the following steps:

[0008] S1. Obtain the profile parameters of the foundation pit retaining structure and the physical and mechanical parameters of the soil; the profile parameters include the excavation depth H of the foundation pit, the length L of the retaining structure and the allowable displacement [S] of the top of the retaining structure; the physical and mechanical parameters of the soil include the friction angle δ between the foundation pit retaining structure and the soil, the internal friction angle and soil weight γ;

[0009] S2, obtain the inclination angle α of the active side sliding crack surface of the foundation pit and the allowable displacement [S] of the top of the retaining structure;

[0010] S3. According to the relationship between the friction angle and the horizontal displacement of the retaining wall, the friction angles at different depths of the retaining structure under non-limiting conditions are calculated for the active side and the passive side respectively:

[0011]

[0012] The subscript x of each parameter is used to distinguish the side where the parameter is located. When the side where the parameter is located is the active side, x=a; when the side where the parameter is located is the passive side, x=p;

[0013] Parameter K on the x side x The calculation formula is:

[0014]

[0015] The parameter z represents the depth distance between the enclosure structure and the ground; and δ are the internal friction angle of soil and the wall-soil friction angle, and δ mx (z) is the value of the internal friction angle of the soil and the wall-soil friction angle at a distance z from the ground on the x side of the retaining structure under non-limiting conditions; and δ0 are the initial soil internal friction angle and the initial wall-soil friction angle; S zx S is the horizontal displacement of the x-side of the enclosure structure from the ground at z; x is the horizontal displacement of the soil on the x side of the retaining structure when it reaches the limit state. For the active side, S a =0.003L, for the passive side Sp = 0.03L;

[0016] S4. Discretize the soil wedge on the active side of the retaining structure into oblique differential units parallel to the sliding surface, and establish the static equilibrium equations of the oblique differential units in the horizontal and vertical directions:

[0017]

[0018] Where: N m is the normal force acting on the side interface of the oblique differential unit enclosure structure; T m is the tangential force acting on the side interface of the oblique differential unit enclosure structure; N p is the normal force acting on the oblique edge of the oblique differential unit; T p is the tangential force acting on the oblique edge of the oblique differential unit; dG is the gravity of the oblique differential unit body;

[0019] The active lateral earth pressure of the retaining structure is calculated by the static equilibrium equations:

[0020]

[0021] Where: p a (z) is the active lateral earth pressure of the retaining structure at a distance z from the ground;

[0022] At the same time, the passive side earth pressure of the retaining structure at different depths from the ground is calculated by Coulomb's passive earth pressure theory;

[0023] S5. According to the length of the retaining structure and the active and passive side earth pressures acting on the retaining structure, the maximum bending moment and maximum shear force of the retaining structure are calculated to determine the material and reinforcement of the retaining structure. After verification, these parameters are used as the final design parameters of the material and reinforcement of the retaining structure.

[0024] Preferably, the soil surfaces on both sides of the foundation pit are horizontal and have no overlying load.

[0025] Preferably, the displacement mode of the enclosure structure is that the cantilever rigid enclosure structure rotates around the bottom of the enclosure structure, and its maximum displacement is located at the top of the enclosure structure.

[0026] Preferably, the inclination angle α of the sliding surface of the active side soil of the retaining structure is determined according to the following formula:

[0027]

[0028] Preferably, the horizontal displacement S of the enclosure structure at side x from the ground z is z Calculated according to the linear relationship:

[0029]

[0030] Preferably, the earth pressure on the active side of the retaining structure is solved according to the static equilibrium equation of the oblique differential unit, and the earth pressure on the passive side is solved according to the Coulomb passive earth pressure theory.

[0031] Preferably, the profile parameters of the foundation pit retaining structure and the physical and mechanical parameters of the soil are determined based on the exploration and design data of the foundation pit retaining structure, and the exploration and design data at least include an engineering geological report and a construction plan.

[0032] As a preferred option, if the soil on the side of the foundation pit maintenance structure is multi-layer soil, the internal friction angle of the soil is The soil weight γ is obtained by weighted average according to the thickness of different soil layers.

[0033] As a preference, the initial soil internal friction angle The initial wall-soil friction angle δ0 is related to the type of retaining structure:

[0034] For buried enclosure structures, δ0 = 0;

[0035] For layered fill or squeeze-in retaining structures,

[0036] For normally consolidated soil, Determine by the following formula:

[0037]

[0038]

[0039] As a preference, when verifying the calculation solutions of the materials and reinforcement of the retaining structure, it is necessary to conduct overall stability verification, anti-overturning verification and anti-uplift verification of the retaining structure in accordance with the current standard "Technical Code for Building Foundation Pit Support" (JGJ 120-2012).

[0040] In a second aspect, the present invention provides a cantilever rigid retaining structure for a non-limit state sand foundation pit, wherein the material and reinforcement of the retaining structure are designed by the design method described in any scheme in the first aspect.

[0041] The beneficial effects of the present invention are as follows: the present invention utilizes the oblique differential unit method and the law of friction angle following the retaining structure to reasonably solve the earth pressure on the retaining structure under the non-limit state, overcomes the defect that the non-limit state of the soil cannot be considered in the classical foundation pit design method, can provide guidance for the design and calculation of the retaining structure more accurately and reasonably, the calculation method is simple and feasible, can reduce the construction cost under the premise of ensuring the safety of the foundation pit retaining structure, and has a good value for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a flow chart of the design calculation method provided by the implementation of the present invention;

[0043] Figure 2 It is a cross-sectional view of a sand foundation pit retaining structure under a non-limiting state provided by the implementation of the present invention;

[0044] Figure 3 It is a force analysis diagram of the active side soil oblique differential unit provided by the implementation of the present invention;

[0045] Figure 4 It is a simplified diagram of the force analysis of the enclosure structure provided by the present invention;

[0046] Figure 5 It is a calculation result diagram of active lateral earth pressure of the retaining structure provided by the present invention;

[0047] Figure 6 It is a calculation result diagram of the passive side earth pressure of the enclosure structure provided by the present invention;

[0048] In the figure: 1 is the ground, 2 is the retaining structure, 3 is the displacement mode of the retaining structure, and 4 is the bottom of the foundation pit. DETAILED DESCRIPTION

[0049] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0050] The present invention provides a basic step flow of a method for designing a cantilever rigid retaining structure for a sand foundation pit under a non-limit state, and the implementation process thereof is described in detail below.

[0051] S1. Obtain the profile parameters of the foundation pit retaining structure and the physical and mechanical parameters of the soil; the profile parameters include the excavation depth H of the foundation pit, the length L of the retaining structure, and the allowable displacement [S] of the top of the retaining structure; the physical and mechanical parameters of the soil include the friction angle between the foundation pit retaining structure and the soil (i.e., the wall-soil friction angle) δ, the internal friction angle of the soil And soil weight γ.

[0052] It should be noted that if the soil on the side of the foundation pit maintenance structure is multi-layered, the internal friction angle of the soil The soil weight γ is obtained by weighted average according to the thickness of different soil layers. The thicker the soil layer, the greater the weight value.

[0053] As a specific implementation of the present invention, the profile parameters of the foundation pit retaining structure and the physical and mechanical parameters of the soil can be determined based on the exploration and design data of the foundation pit retaining structure. The exploration and design data include but are not limited to engineering geological reports and construction plans.

[0054] The foundation pit designed in the present invention should keep the soil surface on both sides level and without overlying load. At the same time, the displacement mode of the retaining structure is that the cantilever rigid retaining structure rotates around the bottom of the retaining structure, and its maximum displacement is located at the top of the retaining structure.

[0055] S2. Obtain the inclination angle α of the active side sliding crack surface of the foundation pit and the allowable displacement [S] of the top of the retaining structure.

[0056] As a specific implementation of the present invention, the inclination angle α of the sliding surface of the active side soil of the enclosure structure is determined according to the following formula:

[0057]

[0058] Right now:

[0059] As a specific implementation of the present invention, when determining the allowable displacement [S] of the top of the enclosure structure, the displacement S at a depth z from the ground is z It can be calculated according to the linear relationship:

[0060]

[0061] S3. According to the relationship between the friction angle and the horizontal displacement of the retaining wall, the friction angle at any depth of the retaining structure under non-limit state is calculated for the active side and the passive side respectively:

[0062]

[0063] The subscript x of each parameter is used to distinguish the side where the parameter is located. When the side where the parameter is located is the active side, x=a; when the side where the parameter is located is the passive side, x=p.

[0064] Parameter K on the x side x The calculation formula is:

[0065]

[0066] The parameter z represents the depth distance between the enclosure structure and the ground; and δ are the internal friction angle of soil and the wall-soil friction angle, and δ mx (z) is the value of the internal friction angle of the soil and the wall-soil friction angle at a distance z from the ground on the x side of the retaining structure under non-limiting conditions; and δ0 are the initial soil internal friction angle and the initial wall-soil friction angle; S zx S is the horizontal displacement of the x-side of the enclosure structure from the ground at z; x is the horizontal displacement of the soil on the x side of the retaining structure when it reaches the limit state, S a and S p are the horizontal displacements when the soil reaches the active limit state and the passive limit state at a certain depth, respectively. For the active side, S a =0.003L, for the passive side S p =0.03L.

[0067] It should be noted that the parameter δ mx (z), S zx , S x , K x It is necessary to distinguish the side where the parameters are located, that is, the x in these parameters needs to be a and p respectively according to whether the side is active or passive. For the active side, the parameters are δ ma (z), S za , S a , K a , for the passive side, the parameters are δ mp (z), S zp , S p , K p .

[0068] As a specific implementation of the present invention, when the allowable displacement of the top of the enclosure structure is [S], the horizontal displacement S of the enclosure structure at the distance from the ground z to the x side is z Calculated according to the linear relationship:

[0069]

[0070] As a specific implementation of the present invention, the initial soil internal friction angle The initial wall-soil friction angle δ0 is related to the type of retaining structure:

[0071] For buried enclosure structures, δ0 = 0;

[0072] For layered fill or squeeze-in retaining structures,

[0073] For normally consolidated soil, Determine by the following formula:

[0074]

[0075]

[0076] S4. Discretize the active side soil wedge of the retaining structure into numerous oblique differential units parallel to the sliding surface, and establish the static equilibrium equations of the oblique differential units in the horizontal and vertical directions:

[0077]

[0078] Where: N m is the normal force acting on the side interface of the oblique differential unit enclosure structure; T m is the tangential force acting on the side interface of the oblique differential unit enclosure structure; N p is the normal force acting on the oblique edge of the oblique differential unit; T p is the tangential force acting on the oblique edge of the oblique differential unit; dG is the gravity of the oblique differential unit body;

[0079] The active lateral earth pressure of the retaining structure is calculated by the static equilibrium equations:

[0080]

[0081] Where: p a (z) is the active lateral earth pressure of the retaining structure at a distance z from the ground;

[0082] At the same time, the passive side earth pressure of the retaining structure at different depths from the ground is calculated by Coulomb's passive earth pressure theory.

[0083] In the above design process, the earth pressure on the active side of the retaining structure is solved according to the static equilibrium equation of the oblique differential unit, and the passive side is solved according to the Coulomb passive earth pressure theory.

[0084] S5. According to the length of the retaining structure and the active and passive side earth pressures acting on the retaining structure, the maximum bending moment and maximum shear force of the retaining structure are calculated to determine the material and reinforcement of the retaining structure. After verification, these parameters are used as the final design parameters of the material and reinforcement of the retaining structure.

[0085] It should be noted that the material and reinforcement of the enclosure structure can be determined based on the maximum bending moment and maximum shear force of the enclosure structure according to relevant structural calculations, which belongs to the existing technology and will not be described in detail. The calculated results can be used as calculation solutions, which need to be verified before they can be used as the final design results. The specific verification method can be adjusted according to actual conditions.

[0086] As a specific implementation method of the present invention, when verifying the calculation solution of the material and reinforcement of the retaining structure, it is necessary to perform the overall stability verification, anti-overturning verification and anti-uplift verification of the retaining structure according to the current standard "Technical Code for Building Foundation Pit Support" (JGJ 120-2012).

[0087] The design method of the cantilever rigid retaining structure of the sand foundation pit under the non-limit state shown in S1 to S5 above is applied to a specific example to demonstrate its specific implementation effect.

[0088] Example

[0089] In this embodiment, Figure 2 As shown in the figure, the foundation pit is excavated from the ground 1, and the retaining structure 2 is set around the foundation pit. The retaining structure can be a retaining wall. The top of the retaining structure 2 is flush with the ground 1, and the bottom is driven into the bearing layer below the bottom surface 4 of the foundation pit. The displacement mode 3 of the retaining structure is that the cantilever rigid retaining structure rotates around the bottom of the retaining structure, so its maximum displacement is located at the top of the retaining structure. Figure 1 The specific design steps in this embodiment are as follows:

[0090] (1) Determine the profile parameters of the foundation pit support and the physical and mechanical parameters of the soil.

[0091] The excavation depth H of the foundation pit is 6.0m, and the length of the support structure L is 10m. The physical and mechanical parameters of the soil are shown in Table 1.

[0092] Table 1 Soil parameters

[0093]

[0094] (2) Determine the inclination angle α of the active side sliding crack surface of the foundation pit and the allowable displacement [S] of the top of the retaining structure, where:

[0095]

[0096] The allowable horizontal displacement [S] of the top of the retaining structure is 0.002m.

[0097] (3) According to the relationship between the friction angle and the horizontal displacement of the retaining wall, the friction angle at any depth z of the retaining structure under the non-limit state is calculated for the active side and the passive side respectively. and δ mx (z), is calculated as follows:

[0098] (3.1) Calculation of friction angle on active side

[0099] Horizontal displacement S of the active side of the enclosure structure at the distance from the ground at the point z under non-limit state za The sizes are as follows:

[0100]

[0101] Assuming that the relationship between the friction angle and the horizontal displacement of the retaining wall is as follows, the friction angle of the active side soil at the distance z from the ground under the non-limit state can be obtained:

[0102]

[0103]

[0104] The parameter z represents the depth distance between the enclosure structure and the ground; and δ are the internal friction angle of soil and the wall-soil friction angle, and δ ma (z) is the value of the internal friction angle of the soil and the wall-soil friction angle at a distance z from the ground on the active side of the retaining structure under non-limit state; and δ0 are the initial soil internal friction angle and the initial wall-soil friction angle; S za S is the horizontal displacement of the active side of the enclosure structure at the distance from the ground at z; a S is the horizontal displacement of the soil on the active side of the retaining structure when it reaches the limit state. a =0.003L.

[0105] Since the passive side soil under the non-limit state only exists in the area from the bottom of the foundation pit to the bottom of the retaining structure, when calculating the soil pressure on the passive side under the non-limit state, the allowable displacement [S] of the top of the retaining structure wall should be converted into the horizontal displacement at the bottom of the pit. The horizontal displacement at the bottom of the pit is represented by a lowercase s instead of the uppercase S in [S], denoted as [s]:

[0106]

[0107] (3.2) Calculation of friction angle on passive side

[0108] Horizontal displacement S of the passive side of the enclosure structure at the distance from the ground z (z ≥ H) under non-limit state zp The sizes are as follows:

[0109]

[0110] The friction angle between the passive side soil and the pit bottom at the non-limit state is:

[0111]

[0112]

[0113] Where: and δ mp (z) is the value of the internal friction angle of the soil and the wall-soil friction angle at a distance z from the ground on the passive side of the enclosure structure under non-limit state; S zp S is the horizontal displacement of the passive side of the enclosure structure at the distance from the ground; p S is the horizontal displacement of the soil on the passive side of the enclosure structure when it reaches the limit state. p =0.03L.

[0114] (4) The soil wedge on the active side of the structure is discretized into numerous oblique differential units parallel to the slip surface, and the static equilibrium equations of the oblique differential units in the horizontal and vertical directions are established:

[0115]

[0116] Where: N m is the normal force acting on the side interface of the oblique differential unit enclosure structure; T m is the tangential force acting on the side interface of the oblique differential unit enclosure structure; N p is the normal force acting on the oblique edge of the oblique differential unit; T p is the tangential force acting on the hypotenuse of the oblique differential unit; dG is the gravity of the oblique differential unit body.

[0117] The active lateral earth pressure of the retaining structure is calculated by the static equilibrium equations:

[0118]

[0119] Where: p a (z) The magnitude of the active lateral earth pressure of the retaining structure at a distance z from the ground.

[0120] In this embodiment, the active lateral earth pressure p of the retaining structure at different depths is obtained. a Distribution Figure 5 shown.

[0121] The passive lateral earth pressure is calculated according to the Coulomb passive earth pressure formula:

[0122]

[0123] Where: p p (z) The magnitude of the passive side earth pressure of the retaining structure at a distance z from the ground.

[0124] In this embodiment, the passive side earth pressure p of the retaining structure at different depths is obtained. p Distribution Figure 6 shown.

[0125] (5) Based on the length of the retaining structure and the soil pressures on the active and passive sides of the retaining structure, calculate the maximum bending moment and maximum shear force of the retaining structure to determine the material and reinforcement of the retaining structure.

[0126] (6) For the solution obtained in step (5), the overall stability and anti-overturning calculation of the retaining structure are verified according to the current standard "Technical Code for Building Foundation Pit Support" (JGJ120-2012). After passing the calculation, it is used as the final design parameters of the retaining structure materials and reinforcement; if the calculation fails, the calculation parameters need to be readjusted.

[0127] In summary, the design calculation method provided in this embodiment can reasonably solve the non-limit earth pressure on the cantilever rigid retaining structure rotating around the bottom of the retaining structure. On this basis, it can provide guidance and assistance for the actual design of the retaining structure.

[0128] The above is only a preferred embodiment of the present invention. Although the present invention has been disclosed as a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the above disclosed methods and technical contents without departing from the scope of the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

Claims

1. A design method for a cantilever rigid retaining structure for a sand foundation pit under non-limiting conditions, characterized in that: The method comprises the following steps: S1. Obtain the cross-sectional parameters of the foundation pit retaining structure and the physical and mechanical parameters of the soil; the cross-sectional parameters include the excavation depth H of the foundation pit, the length L of the retaining structure, and the allowable displacement [S] of the top of the retaining structure; the physical and mechanical parameters of the soil include the friction angle δ between the foundation pit retaining structure and the soil, the internal friction angle δ of the soil, and the relative humidity. and soil weight γ; S2. Obtain the inclination angle α of the active side sliding crack surface of the foundation pit and the allowable displacement [S] of the top of the retaining structure; S3. Based on the relationship between the friction angle and the horizontal displacement of the retaining wall, calculate the friction angle at different depths of the retaining structure under non-limiting conditions for the active and passive sides respectively: The subscript x of each parameter is used to distinguish the side where the parameter is located. When the side where the parameter is located is the active side, x=a; when the side where the parameter is located is the passive side, x=p; Parameter K on the x side x The calculation formula is: Parameter z represents the depth distance between the enclosure structure and the ground; and δ are the internal friction angle of soil and the wall-soil friction angle, and δ mx (z) is the value of the internal friction angle of the soil and the wall-soil friction angle at a distance z from the ground on the x side of the retaining structure under the non-limiting state; and δ0 are the initial soil internal friction angle and the initial wall soil friction angle; S zx S is the horizontal displacement of the x-side of the enclosure structure from the ground at point z; x is the horizontal displacement of the soil on the x side of the retaining structure when it reaches the limit state. For the active side, S a =0.003L, for the passive side S p =0.03L; S4. Discretize the soil wedge on the active side of the retaining structure into oblique differential units parallel to the sliding surface, and establish the static equilibrium equations of the oblique differential units in the horizontal and vertical directions: Where: N m is the normal force acting on the side interface of the oblique differential unit enclosure structure; T m is the tangential force acting on the side interface of the oblique differential unit enclosure structure; N p is the normal force acting on the oblique side of the oblique differential unit; T p is the tangential force acting on the oblique side of the oblique differential unit; dG is the gravity of the oblique differential unit body; The active side earth pressure of the retaining structure is calculated by the static equilibrium equations: Where: p a (z) is the active side earth pressure of the retaining structure at a distance z from the ground; At the same time, the passive side earth pressure of the retaining structure at different depths from the ground is calculated using Coulomb's passive earth pressure theory; S5. Based on the length of the retaining structure and the active and passive side earth pressures acting on the retaining structure, calculate the maximum bending moment and maximum shear force of the retaining structure, thereby determining the material and reinforcement of the retaining structure. After verification, these parameters are used as the final design parameters of the retaining structure material and reinforcement.

2. The design method of cantilever rigid retaining structure for sand foundation pit under non-limit state according to claim 1 is characterized in that: The soil surfaces on both sides of the foundation pit are horizontal and have no overlying load.

3. The design method of cantilever rigid retaining structure for sand foundation pit under non-limit state according to claim 1 is characterized in that: The displacement mode of the enclosure structure is that the cantilever rigid enclosure structure rotates around the bottom of the enclosure structure, and its maximum displacement is located at the top of the enclosure structure.

4. The design method of cantilever rigid retaining structure for sand foundation pit under non-limit state according to claim 1 is characterized in that: The inclination angle α of the sliding surface of the active side soil of the retaining structure is determined according to the following formula:

5. The design method of cantilever rigid retaining structure for sand foundation pit under non-limit state according to claim 1 is characterized in that: The horizontal displacement S of the enclosure structure at side x from the ground at point z z Calculated according to the linear relationship:

6. The method for designing a cantilever rigid retaining structure for a sand foundation pit under non-limiting conditions according to claim 1 is characterized in that: The earth pressure on the active side of the retaining structure is solved according to the static equilibrium equation of the oblique differential unit, and the earth pressure on the passive side is solved according to the Coulomb passive earth pressure theory.

7. The design method of cantilever rigid retaining structure for sand foundation pit under non-limit state according to claim 1 is characterized in that: The cross-sectional parameters of the foundation pit retaining structure and the physical and mechanical parameters of the soil are determined based on the exploration and design data of the foundation pit retaining structure, which at least includes an engineering geological report and a construction plan. If the soil on the side of the foundation pit retaining structure is multi-layered, the internal friction angle of the soil is The soil weight γ is obtained by weighted average according to the thickness of different soil layers.

8. The method for designing a cantilever rigid retaining structure for a sand foundation pit under non-limiting conditions according to claim 1 is characterized in that: The initial soil internal friction angle The initial wall-soil friction angle δ0 is related to the type of retaining structure: For buried enclosure structures, δ0 = 0; For layered fill or squeeze-in enclosure structures, take For normally consolidated soil, Determine as follows:

9. The method for designing a cantilever rigid retaining structure for a sand foundation pit under non-limiting conditions according to claim 1 is characterized in that: When verifying the calculation solutions of the materials and reinforcement of the retaining structure, it is necessary to conduct overall stability verification, anti-overturning verification and anti-uplift verification of the retaining structure in accordance with the current standard "Technical Code for Building Foundation Pit Support" (JGJ 120-2012).

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