Deformation calculation method of pile foundation beside foundation pit considering deformation of enclosure and load on top of pile

Abstract

The application discloses a kind of considering enclosure deformation and pile top load's foundation pit side pile foundation deformation calculation method, including establishing calculation model;Enclosure deformation mode selection;Consider the deformation calculation of foundation pit enclosure of space effect;Foundation pit side wall unloading quantity calculation;Additional stress calculation of pile foundation caused by foundation pit excavation;Adjacent single pile deformation calculation caused by foundation pit excavation These steps.The application considers four typical foundation pit enclosure deformation modes and pile top vertical load effect, fully considers the actual situation, and can quickly and accurately calculate the horizontal displacement and bending moment of adjacent single pile caused by foundation pit excavation.

Description

Technical Field

[0001] This invention belongs to the field of underground engineering, specifically relating to a method for calculating the deformation of pile foundations on the side of a foundation pit, taking into account the deformation of the retaining structure and the load on the pile top. Background Technology

[0002] With the further development of urban underground space, more and more foundation pit projects are located near buildings and urban infrastructure. The excavation and unloading of foundation pits will cause additional internal forces and deformations in the pile foundations of nearby buildings, overpasses, etc. Excessive deformation will threaten the safety of the pile foundation itself and the superstructure. Therefore, studying the impact of foundation pit excavation and unloading on adjacent pile foundations is of great significance.

[0003] Currently, most studies on the impact of foundation pit excavation on adjacent pile foundation deformation first calculate the soil deformation caused by foundation pit excavation based on the image source method, and then apply the soil deformation to the adjacent pile foundation. Zhang Aijun et al. (Zhang Aijun, Mo Haihong, Li Aiguo, et al. Two-stage analysis method for the influence of foundation pit excavation on adjacent pile foundation [J]. Chinese Journal of Rock Mechanics and Engineering, 2013, 32(Supplement 1):2746-2750.) obtained the displacement field of the soil around the foundation pit based on the image source method, and derived the analytical solution of the lateral response of foundation pit excavation to adjacent pile foundation based on the Winkler foundation model; Liang Yunfa et al. (Liang Yunfa, Li Yanchu, Huang Maosong. Simplified analysis method of horizontal pile based on Pasternak two-parameter foundation model [J]. Chinese Journal of Geotechnical Engineering) ,2013,35(Supplement 1):300-304.) Further, the Pasternak two-parameter foundation model was introduced to analyze the horizontally loaded piles, taking into account the shearing effect of the soil and the characteristics of the uneven distribution of soil parameters along the vertical direction; Zhang Zhiguo et al. (Zhang Zhiguo, Zhao Qihua, Xu Chen, et al. Simplified analysis of the influence of foundation pit excavation on adjacent single piles based on image source method [J]. Rock and Soil Mechanics,2016,37(7):2011-2020.) introduced the Kerr foundation model and derived the displacement solution of the pile foundation under the influence of the side foundation pit excavation. However, the image source method assumes the uniformity of soil convergence, while Lin Cungang et al. (Lin Cungang, Xia Tangdai, Liang Rongzhu, et al. Virtual mirror algorithm for ground settlement during shield tunneling [J]. Chinese Journal of Geotechnical Engineering, 2014, 36(8): 1438-1446.) pointed out that the assumption of uniform soil convergence is inconsistent with reality, and the actual soil convergence should be non-uniform. In addition, some studies have obtained the additional stress on the adjacent pile foundation caused by the excavation of the foundation pit based on the stress release method. For example, Yang Tao et al. (Yang Tao, Tong Liyuan, Li Dan. Deformation and stress response of highway bridge pile foundation caused by excavation of foundation pit [J]. Journal of Building Science and Engineering, 2020, 37(5): 214-222.) obtained the additional stress on the adjacent pile foundation caused by the excavation of the foundation pit based on the stress release method, solved the deflection differential equation of the bridge pile foundation under the action of additional stress in the Kerr model, and obtained the deflection curve of the pile foundation. However, the study simply considers the side wall unloading as a triangular distribution, without considering the impact of the deformation of the retaining structure on the additional stress caused by the excavation of the foundation pit; in addition, as a load-bearing component, the pile top generally has a vertical load, but most current theoretical studies on the deformation of piles on the side of the foundation pit do not consider the impact of the vertical load on the pile top on the horizontal displacement of the pile; at present, the cumulative maximum deformation of the retaining structure is the main control index during the construction of the foundation pit, but even if the maximum deformation of the retaining structure is the same, the different deformation modes may lead to differences in the deformation of the surrounding soil or pile foundation. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a method for calculating the deformation of pile foundations on the side of the foundation pit, taking into account the deformation of the retaining structure and the load on the pile top. The specific technical solution is as follows:

[0005] A method for calculating the deformation of pile foundations on the side of an excavation pit, considering the deformation of the retaining structure and the load on the pile top, includes the following steps:

[0006] Step 1: Establish a mechanical model

[0007] A rectangular foundation pit has a single pile on its side. A coordinate system is established at the center o of the foundation pit on the ground. The two vertical directions on the horizontal plane are the x-axis and y-axis, and the depth direction of the foundation pit is the positive z-axis. The excavation depth of the foundation pit is d, the excavation length is L, the width is B, and the length of the retaining structure is H. The diameter of the adjacent single pile is D, the length is l, the distance of the retaining structure parallel to the y-axis from the single pile is s, and the distance of the retaining structure parallel to the x-axis from the single pile is h. All the above parameters are in meters.

[0008] Step 2: Select the deformation mode of the retaining structure based on the on-site support conditions, and calculate the horizontal displacement u(z) of the retaining structure of the foundation pit;

[0009] Step 3: Calculate the deformation at any point of the foundation pit retaining structure:

[0010] u(λ,z)=u(z)·PSR(λ,d)

[0011] In the formula, u(λ, z) represents the deformation of the retaining structure at a distance of λ from the nearest corner of the foundation pit and a depth of z; PSR(λ, d) represents the plane strain ratio PSR of the retaining structure at a distance of λ from the nearest corner of the foundation pit and a depth of z.

[0012]

[0013] Step 4: Calculate the unloading amount of the foundation pit sidewalls. The unloading amount of the foundation pit sidewalls is the difference in earth pressure on the retaining structure before and after soil excavation. The calculation formula is:

[0014]

[0015] In the formula, p c (λ,z) ​​represents the unloading amount on the sidewall at a distance of λ from the nearest corner of the foundation pit and a depth of z; e a (λ,z) ​​represents the active earth pressure at a location λ and z closest to the corner of the foundation pit; u acr This represents the displacement required for the soil to reach its active limit state, and is generally taken as u. acr =0.001H~0.003H; e0(λ,z),e acr (λ, z) represent the static earth pressure and the ultimate active earth pressure at a distance of λ from the corner of the foundation pit and a depth of z, respectively.

[0016] Step 5: Calculate the additional stress on the pile foundation caused by the excavation of the foundation pit.

[0017] Consider a small element dζdη at a point (B / 2, ζ, η) on the foundation pit retaining structure. The unloading effect of this element on the soil is p. c The horizontal additional stress at any point (x1, y1, z1) on the adjacent single pile axis caused by the excavation of the foundation pit is obtained by integral calculation of (L / 2-ζ,η)dζdη in the unloading distribution area of ​​the retaining structure:

[0018]

[0019] In the formula:

[0020] μ is the Poisson's ratio of the soil;

[0021] Step 6: Calculate the deformation of adjacent single piles caused by foundation pit excavation.

[0022] [K t ][w]-[K N [w]+[K s [w] = [Q]

[0023] In the formula, [K t [K] represents the pile foundation displacement stiffness matrix; N [K] represents the vertical load influence matrix; s [w] is the foundation stiffness matrix; [q] is the column vector of pile foundation horizontal displacement; [Q] is the column vector of additional load.

[0024] Where: [Q] = D[q0 q1 q2 ... q n ] T

[0025] [w] = [w0 w1 w2 ... w] n ] T

[0026]

[0027]

[0028]

[0029] In the formula, l' = l / n, where n represents dividing the pile into n equal parts, numbered 0, 1, ..., n-1, n from the pile top to the pile bottom; EI is the equivalent stiffness of the pile foundation; N is the vertical load on the pile top, with downwards being positive; D is the pile diameter; and k is the soil reaction coefficient, calculated using the Vesic formula. Where E0 is the elastic modulus of the foundation soil; q(z1) is the additional load caused by the excavation of the foundation pit, q(z1) = σ x (z1);

[0030] Given the additional load q(z1) and the vertical load N at the top of the pile, the horizontal displacement of the adjacent single pile caused by the excavation of the foundation pit can be solved by combining the above calculation formula.

[0031] Furthermore, the deformation modes of the enclosure structure in step 2 include the following four types:

[0032] (1) Cantilever deformation mode:

[0033] In the formula, u(z) represents the displacement of the sidewall into the pit at depth z; δ max This represents the maximum displacement of the sidewall.

[0034] (2) Kick-type transformation mode

[0035] The deformation curve of the enclosure structure was fitted using a polynomial. Constraints were set to allow the top to be fixed and the bottom to be translational to simulate the deformation mode of the skirting board. The formula for calculating the horizontal displacement of the enclosure structure was obtained as follows:

[0036]

[0037] (3) Convex deformation mode

[0038]

[0039] Where: δ i (z,d i ) represents the deformation value of the retaining structure at depth z caused by the excavation of the i-th layer, and d i δ represents the excavation depth of the i-th layer; max i This represents the maximum deformation value of the retaining structure caused by the excavation of the i-th layer.

[0040] The ratio δ of the cumulative maximum deformation of the retaining structure to the excavation depth. max If / d is used as a control parameter, and the deformation of the retaining structure during each excavation satisfies the control parameter, then the sidewall deformation caused by the excavation of the i-th layer is:

[0041]

[0042] After excavating layer m, the depth of the pit bottom is d. i At that time, the displacement of the sidewall is:

[0043]

[0044] (4) Composite deformation mode:

[0045]

[0046] Furthermore, when the retaining structure is an internally supported type, the internally convex deformation mode or the composite deformation mode is selected; when the retaining structure is inserted relatively shallowly into the soft soil layer, the deformation of the foundation pit retaining structure is a kick-type deformation mode with the largest bottom displacement; when the retaining structure is a cantilever support, the cantilever deformation mode is selected.

[0047] The beneficial effects of this invention are as follows:

[0048] (1) This invention fully combines the actual site conditions, considers the deformation mode of typical foundation pit retaining structures and the vertical load on the pile top, and can quickly calculate the horizontal displacement of adjacent single piles caused by foundation pit excavation, and the calculated value has a small error with the test value.

[0049] (2) By comparing the maximum horizontal displacement of the pile body calculated by the method of the present invention with the design allowable value, the safety of the pile foundation used in the adjacent foundation pit can be effectively assessed. Attached Figure Description

[0050] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0051] Figure 1 This is a schematic diagram of the relative positions of the foundation pit and the adjacent pile foundation in an embodiment of the present invention. (a) is a top view, and (b) is a front view.

[0052] Figure 2 The diagram shows the sidewall deformation calculation model of the typical deformation mode of the enclosure structure in the embodiment of the present invention, where (a) is a cantilever type, (b) is a kickboard type, (c) is an inward convex type, and (d) is a composite type.

[0053] Figure 3 The diagram shows the pile-soil interaction calculation model in this embodiment of the invention; where (a) represents the pile-soil interaction diagram and (b) represents the finite difference diagram.

[0054] Figure 4 The diagram shows the deformation of a single pile under different deformation modes of the retaining structure in Embodiment 1 of the present invention.

[0055] Figure 5 This is a diagram of the bending moment of a single pile under different deformation modes of the retaining structure in Embodiment 1 of the present invention.

[0056] Figure 6 The diagram shows the deformation of a single pile under different deformation modes of the retaining structure in Embodiment 2 of the present invention. Detailed Implementation

[0057] The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. The purpose and effects of the present invention will become clearer. It should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0058] The method for calculating the deformation of pile foundations on the side of the foundation pit, considering the deformation of the retaining structure and the load on the pile top, as described in this embodiment, includes the following steps:

[0059] 1. Establish a mechanical model

[0060] like Figure 1 As shown, a rectangular foundation pit has a single pile beside it. A coordinate system is established at the center o of the foundation pit on the ground. The pit depth is d (m); the excavation length is L (m); the width is B (m); and the length of the retaining structure is H (m). The diameter of the adjacent single pile is D (m); the length is l (m); the distance from the retaining structure parallel to the y-axis to the single pile is s (m); and the distance from the retaining structure parallel to the x-axis to the single pile is h (m).

[0061] 2. Selection of Deformation Mode of Envelope

[0062] like Figure 2 As shown, the deformation mode of the retaining structure is selected based on the on-site support conditions. Generally, the internal support type selects either an inward-convex deformation mode or a composite deformation mode. When the retaining structure is shallowly inserted into the soft soil layer, the deformation of the foundation pit retaining structure exhibits the kick-toe deformation mode with the largest bottom displacement. For cantilever support, the cantilever mode is selected. The calculation methods for the sidewall deformation curves under the four retaining structure deformation modes are as follows:

[0063] Cantilever deformation mode:

[0064] The deformation curve of the side wall piles in the middle of the foundation pit is

[0065]

[0066] In the formula: u(z) is the displacement of the sidewall into the pit at depth z; δ max This represents the maximum displacement of the sidewall.

[0067] Kick-type transformation mode

[0068] The deformation curve of the enclosure structure was fitted using a polynomial. Constraints were set to allow the top to be fixed and the bottom to be translated to simulate the deformation mode of the skirting board. The formula for calculating the horizontal displacement of the enclosure structure was then obtained.

[0069]

[0070] Considering the skirting-type deformation mode, the deformation at the bottom of the enclosure structure reaches its maximum value, i.e., u(H)=δ. max Substituting into equation (2), we get: α=2δ maxTherefore, equation (2) can be rewritten as:

[0071]

[0072] Convex deformation mode

[0073]

[0074] Where: δ max i d represents the maximum deformation of the retaining structure caused by the excavation of the i-th layer; i δ represents the excavation depth of the i-th layer; i (z,d i ) represents the deformation value of the retaining structure at depth z caused by the excavation of the i-th layer.

[0075] The ratio δ of the cumulative maximum deformation of the retaining structure to the excavation depth. max If / d is used as a control parameter, and the deformation of the retaining structure during each excavation satisfies the control parameter, then the sidewall deformation caused by the excavation of the i-th layer is:

[0076]

[0077] After excavating layer m, the depth of the pit bottom is d. i At that time, the displacement of the sidewall is:

[0078]

[0079] Composite Deformation Mode

[0080] Based on measured data from typical deep foundation pit projects, the formula for calculating the lateral deformation curve on the central plane of the retaining structure is as follows:

[0081]

[0082] 3. Deformation calculation of foundation pit retaining structure considering spatial effects

[0083] Due to factors such as differences in support stiffness, the deformation of the retaining structure exhibits a significant spatial effect, with deformation being smaller at the corners of the pit and larger in the central region. The plane strain ratio (PSR) (the ratio of the retaining structure's displacement under three-dimensional simulation conditions to its displacement under plane strain conditions) is used to quantitatively describe the influence of this spatial effect. The fitted formula for calculating PSR is as follows:

[0084]

[0085] In the formula, λ is the horizontal distance from any point on the retaining structure to the nearest corner of the foundation pit.

[0086] When the excavation depth of the foundation pit is d, the deformation calculation formula for any point on the retaining structure is:

[0087] u(λ,z)=u(z)·PSR(λ,d) (9)

[0088] In the formula, u(λ, z) represents the deformation of the retaining structure at a distance of λ from the nearest corner of the foundation pit and a depth of z.

[0089] 4. Calculation of unloading volume of foundation pit sidewalls

[0090] By fitting the relationship between relaxation stress and displacement, a method for calculating active earth pressure that considers displacement is proposed, and its calculation formula is as follows:

[0091]

[0092] In the formula: e a (λ,z) ​​represents the active earth pressure at a location λ and z closest to the corner of the foundation pit; u acr This represents the displacement required for the soil to reach its active limit state, and is generally taken as u. acr =0.001H~0.003H; e0(λ,z),e acr (λ, z) represent the at-rest earth pressure and the ultimate active earth pressure at a distance of λ from the nearest corner of the excavation pit and a depth of z, respectively. The sidewall unloading is the difference in earth pressure on the retaining structure before and after excavation, and its calculation formula is:

[0093]

[0094] In the formula p c (λ,z) ​​represents the unloading amount of the sidewall at a distance of λ from the nearest corner of the foundation pit and a depth of z.

[0095] 5. Calculation of additional stress on pile foundations caused by foundation pit excavation

[0096] Consider a small element dζdη at a point (B / 2, ζ, η) on the foundation pit retaining structure. The unloading effect of this element on the soil is p. c The horizontal additional stress at any point (x1, y1, z1) on the adjacent single pile axis caused by the excavation of the foundation pit is obtained by integral calculation of (L / 2-ζ,η)dζdη in the unloading distribution area of ​​the retaining structure:

[0097]

[0098] In the formula:

[0099] μ is the Poisson's ratio of the soil.

[0100] 6. Calculation of deformation of adjacent single piles caused by foundation pit excavation

[0101] The following basic assumptions are made for the pile-soil interaction model on the Winkler foundation:

[0102] 1) The pile foundation is equivalent to an Euler-Bernoulli beam in the longitudinal direction; 2) The shear effect of the soil is not considered; 3) The deformation of the pile foundation is coordinated with the surrounding soil; 4) The axial force generated by the deflection of the pile is not considered.

[0103] Under the action of the additional load q(z1) and the external load N, the equilibrium differential equation of the horizontal displacement w(z1) of the pile foundation is:

[0104]

[0105] In the formula: EI is the equivalent stiffness of the pile foundation; N is the vertical load on the pile top, with downward being positive; D is the pile diameter; k is the soil reaction coefficient, calculated using the Vesic formula. Where E0 is the elastic modulus of the foundation soil; q(z1) is the additional load caused by the excavation of the foundation pit, q(z1) = σ x (z1) is determined by equation (12) in step 5.

[0106] like Figure 3 As shown, the pile is divided into n equal parts, and the pile top to pile bottom are numbered 0, 1, ..., n-1, n respectively. Two virtual nodes are added to both the pile bottom and the pile top. Equation (13) can be written in difference form as follows:

[0107]

[0108] In the formula: l'=l / n.

[0109] Equation (14) can be written in matrix form as follows:

[0110] [K t ][w]-[K N [w]+[K s [w]=[Q] (15)

[0111] In the formula: [K t [K] represents the pile foundation displacement stiffness matrix; N [K] represents the vertical load influence matrix; s [ ] represents the foundation stiffness matrix; [w] represents the column vector of pile foundation horizontal displacement; [Q] represents the column vector of additional load. Where:

[0112] [Q] = D[q0 q1 q2 ... q] n ] T (16)

[0113] [w] = [w0 w1 w2 ... w] n ] T (17)

[0114]

[0115] If the pile base is fixed, then the boundary condition for the pile top to be free is:

[0116]

[0117]

[0118] w n =0 (21)

[0119]

[0120] Combining equations (19-22), we can obtain:

[0121]

[0122]

[0123] Given the additional load q(z1) and the vertical load N at the pile top, the horizontal displacement of the adjacent single pile caused by the excavation of the foundation pit can be solved by combining equations (14-24). The above calculation process is performed numerically using Matlab programming.

[0124] Two specific embodiments were selected, and the horizontal displacement curves of adjacent single piles caused by foundation pit excavation were calculated using the method of this application. The results were then compared with the corresponding measured values ​​to verify the reliability of the calculation method of this application.

[0125] Example 1

[0126] A foundation pit has a length L = 127.5m, a width B = 20m, and a depth d = 16m, with 6 internal supports. The retaining structure is a 0.8m thick diaphragm wall with a length H = 31m. The adjacent single pile has a diameter D = 1m, a length l = 46m, and a bending stiffness EI = 5 × 10⁻⁶. 4 kN·m 2 The pile head is free, and the distance from the pile axis to the outer side of the diaphragm wall is s = 3m. The Poisson's ratio of the soil is μ = 0.25. In this embodiment, the deformation mode of the foundation pit retaining structure is a composite deformation mode.

[0127] Control parameter δ for the deformation of the enclosure structure in Example 1 max When / d is all taken as 0.12%, the deformation curves of adjacent single piles caused by the four retaining structure deformation modes are as follows: Figure 4 As shown. By Figure 3 It can be seen that the maximum deformation of the pile is 28.3 mm. The pile deformation has not reached the control value and is in a safe state. The deformation of the adjacent single pile caused by the composite deformation mode of the foundation pit retaining structure is in good agreement with the actual measurement.

[0128] Figure 5The diagram shows the bending moment of adjacent single piles under the four deformation modes of the foundation pit retaining structure in Example 1. The bending moment distribution patterns of the piles caused by the convex and composite deformation modes are similar, and the maximum bending moment is the largest among the four deformation modes, followed by the cantilever mode, and the smallest is the kick-toe mode.

[0129] Example 2:

[0130] A foundation pit is located in Yuhuatai District, Nanjing City. It is 120m long, 13m wide, and 10m deep. [8] The soil within the excavation depth range mainly consists of miscellaneous fill, silty clay, and silt. The retaining structure is a diaphragm wall with a depth of H = 19m, and three internal supports are installed within the pit. A separate bored pile with a diameter of D = 0.8m and a length of l = 22m, with a free top, was driven at a distance s = 4m behind the diaphragm wall. The bending stiffness of the pile was taken as EI = 4 × 10⁻⁶. 4 kN·m 2 In this case, the deformation mode of the foundation pit retaining structure is an inward convex mode.

[0131] Control parameter δ for the deformation of the enclosure structure in Example 2 max When / d is all taken as 0.2%, the deformation curves of adjacent single piles caused by the four retaining structure deformation modes are as follows: Figure 6 As shown. By Figure 6 It can be seen that the maximum deformation of the pile is 28.1 mm, and the pile is in a safe state. The deformation of the adjacent single pile caused by the inward convex deformation mode of the foundation pit retaining structure is in good agreement with the actual measurement.

[0132] In actual foundation pit excavation, the deformation of the retaining structure is not uniform; different cross-sections may exhibit different deformation patterns (including cantilever and kick-off). The model of this invention is a comprehensive deformation model that integrates different deformation patterns across various cross-sections. The specific deformation pattern can be selected based on the actual engineering requirements.

[0133] It will be understood by those skilled in the art that the above descriptions are merely preferred examples of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. All modifications and equivalent substitutions made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A method for calculating the deformation of pile foundations on the side of an excavation pit, considering the deformation of the retaining structure and the load on the pile top, characterized in that, Includes the following steps: Step 1: Establish a mechanical model A rectangular foundation pit has a single pile on its side. A coordinate system is established at the center o of the foundation pit on the ground. The two vertical directions on the horizontal plane are the x-axis and y-axis, and the depth direction of the foundation pit is the positive z-axis. The excavation depth of the foundation pit is d, the excavation length is L, the width is B, and the length of the retaining structure is H. The diameter of the adjacent single pile is D, the length is l, the distance of the retaining structure parallel to the y-axis from the single pile is s, and the distance of the retaining structure parallel to the x-axis from the single pile is h. All the above parameters are in meters. Step 2: Select the deformation mode of the retaining structure based on the on-site support conditions, and calculate the horizontal displacement u(z) of the retaining structure of the foundation pit; Step 3: Calculate the deformation at any point of the foundation pit retaining structure: u(λ,z)=u(z)·PSR(λ,d) In the formula, u(λ, z) represents the deformation of the retaining structure at a distance of λ from the nearest corner of the foundation pit and a depth of z; PSR(λ, d) represents the plane strain ratio PSR of the retaining structure at a distance of λ from the nearest corner of the foundation pit and a depth of z. Step 4: Calculate the unloading amount of the foundation pit sidewalls. The unloading amount of the foundation pit sidewalls is the difference in earth pressure on the retaining structure before and after soil excavation. The calculation formula is: In the formula, p c (λ,z) ​​represents the unloading amount on the sidewall at a distance of λ from the nearest corner of the foundation pit and a depth of z; e a (λ,z) ​​represents the active earth pressure at a location λ and z closest to the corner of the foundation pit; u acr This represents the displacement required for the soil to reach its active limit state, and is generally taken as u. acr =0.001H~0.003H; e0(λ,z),e acr (λ, z) represent the static earth pressure and the ultimate active earth pressure at a distance of λ from the corner of the foundation pit and a depth of z, respectively. Step 5: Calculate the additional stress on the pile foundation caused by the excavation of the foundation pit. Consider a small element dζdη at a point (B / 2, ζ, η) on the foundation pit retaining structure. The unloading effect of this element on the soil is p. c The horizontal additional stress at any point (x1, y1, z1) on the adjacent single pile axis caused by the excavation of the foundation pit is obtained by integral calculation of (L / 2-ζ,η)dζdη in the unloading distribution area of ​​the retaining structure: In the formula: μ is the Poisson's ratio of the soil; Step 6: Calculate the deformation of adjacent single piles caused by foundation pit excavation. [K t ][w]-[K N ][w]+[K s ][w]=[Q] In the formula, [K t [K] represents the pile foundation displacement stiffness matrix; N [K] represents the vertical load influence matrix; s [w] is the foundation stiffness matrix; [q] is the column vector of pile foundation horizontal displacement; [Q] is the column vector of additional load. Where: [Q] = D[q0 q1 q2 ... q n ] T [in]=[in0 in1 in2 ... in n ] T In the formula, l' = l / n, where n represents dividing the pile into n equal parts, numbered 0, 1, ..., n-1, n from the pile top to the pile bottom; EI is the equivalent stiffness of the pile foundation; N is the vertical load on the pile top, with downwards being positive; D is the pile diameter; and k is the soil reaction coefficient, calculated using the Vesic formula. Where E0 is the elastic modulus of the foundation soil; q(z1) is the additional load caused by the excavation of the foundation pit, q(z1) = σ x (z1); Given the additional load q(z1) and the vertical load N at the top of the pile, the horizontal displacement of the adjacent single pile caused by the excavation of the foundation pit can be solved by combining the above calculation formula.

2. The method for calculating the deformation of pile foundations on the side of the foundation pit considering the deformation of the retaining structure and the load on the pile top, as described in claim 1, is characterized in that... The deformation modes of the enclosure structure in step 2 include the following four: (1) Cantilever deformation mode: In the formula, u(z) represents the displacement of the sidewall into the pit at depth z; δ max This represents the maximum displacement of the sidewall. (2) Kick-type transformation mode The deformation curve of the enclosure structure was fitted using a polynomial. Constraints were set to allow the top to be fixed and the bottom to be translational to simulate the deformation mode of the skirting board. The formula for calculating the horizontal displacement of the enclosure structure was obtained as follows: (3) Convex deformation mode Where: δ i (z,d i ) represents the deformation value of the retaining structure at depth z caused by the excavation of the i-th layer, and d i δ represents the excavation depth of the i-th layer; maxi This represents the maximum deformation value of the retaining structure caused by the excavation of the i-th layer. The ratio δ of the cumulative maximum deformation of the retaining structure to the excavation depth. max If / d is used as a control parameter, and the deformation of the retaining structure during each excavation satisfies the control parameter, then the sidewall deformation caused by the excavation of the i-th layer is: After excavating layer m, the depth of the pit bottom is d. i At that time, the displacement of the sidewall is: (4) Composite Deformation Mode 3. The method for calculating the deformation of pile foundations on the side of the foundation pit considering the deformation of the retaining structure and the pile top load according to claim 2, characterized in that, When the retaining structure is internally supported, choose the convex deformation mode or the composite deformation mode; when the retaining structure is shallowly inserted into the soft soil layer, the deformation of the foundation pit retaining structure is the kick-type deformation mode with the largest bottom displacement; when the retaining structure is cantilever support, choose the cantilever deformation mode.

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