Calculation method of soil pressure of foundation pit considering stress transfer near existing underground structure

Abstract

The application discloses a kind of foundation pit earth pressure calculation method considering the stress transmission of approaching existing underground structure, first according to actual engineering project, relevant stratum parameters are collected as basic parameters.Then determine the position parameters of existing structure and newly-built foundation pit, determine the stratum fracture surface of foundation pit construction, calculate the additional stress transmission of existing structure, in this process, relevant stratum parameters collected and corresponding soil slip surface failure angle, internal friction angle etc. are needed.Then the calculation formula of earth pressure is deduced by thin layer element method, finally the calculation formula deduced is used to calculate earth pressure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of foundation pit support, in particular to a foundation pit earth pressure calculation method considering stress transmission of adjacent existing underground structure. BACKGROUND

[0002] With the acceleration of urbanization, underground engineering development and utilization are increasing, and the construction environment is more complex. Open excavation foundation pit engineering becomes an important part of foundation and underground engineering construction. During the excavation of adjacent lateral open foundation pit, the form considering the influence of additional stress of existing structure is considered, the earth pressure becomes complex, which is related to the safety of the foundation pit itself, the safety of adjacent buildings and the normal operation of nearby traffic. Earth pressure is the basis for safety evaluation. In the patent CN113128061A, a method for obtaining earth pressure of adjacent underground engineering non-synchronous construction is disclosed, but the influence of additional stress of existing structure is not considered, which is different from the actual situation. Therefore, it is particularly important to calculate the earth pressure of adjacent lateral open foundation pit, especially considering the influence of additional stress of existing structure on new foundation pit during foundation pit excavation. SUMMARY

[0003] To solve the above technical problems, the present application provides a complete technical solution, a foundation pit earth pressure calculation method considering stress transmission of adjacent existing underground structure. During the foundation pit excavation process, when the existing station and the enclosure structure have a certain distance, the stress of the enclosure structure will be affected by the existing structure when the failure mode is the failure mode of the present application. The stress of the enclosure structure during the foundation pit excavation process should consider the additional stress influence of the existing structure. According to this failure mode, the earth pressure formula is derived, and the corresponding earth pressure is obtained.

[0004] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0005] The present application proposes a foundation pit earth pressure calculation method considering stress transmission of adjacent existing underground structure, as follows:

[0006] Step 1: Obtain the stratum parameters;

[0007] Step 2: Obtain the position parameters of the existing structure and the new foundation pit structure;

[0008] Step 3: Determine the foundation pit construction stratum fracture surface and each sliding block according to the position parameters of the existing structure and the new foundation pit structure;

[0009] Step 4: Determine the additional stress transmission of the existing structure;

[0010] Step 5: Calculate the earth pressure of each sliding block.

[0011] As a further technical solution, in step 3, the determination method of the foundation pit construction stratum rupture surface is as follows:

[0012] The soil slip failure angle θ generated when the station is destroyed, the distance h from the ground to the upper surface of the station j , the station height h0, the distance h s from the lower surface of the station to the pile bottom, and the distance b from the left edge of the station to the right edge of the pile in the horizontal direction are used as the basis to determine the rupture surface generated by the foundation pit construction stratum; wherein The soil friction angle is φ.

[0013] As a further technical solution, according to the foundation pit construction stratum rupture surface, three slip blocks are determined, the first slip block is the slip block at the top of the existing structure; the second slip block is the slip block formed by the side of the existing structure and the side of the newly built foundation pit; and the third slip block is the slip block at the bottom of the existing structure.

[0014] As a further technical solution, the slip surface of the first slip block is a point on the upper part of the existing structure extending to the ground along the failure angle θ.

[0015] As a further technical solution, the slip surface of the third slip block is the slip surface of the slip block formed by the slip surface of the pile bottom of the enclosure pile to a point on the lower part of the existing structure along the rupture angle θ.

[0016] As a further technical solution, in step 4, the additional stress transmitted by the existing structure is:

[0017]

[0018] Wherein, β1 is the stress loss rate of the foundation pit enclosure structure, K0 is the static earth pressure coefficient The internal friction angle is φ, the soil bulk density is γ, f is the distance from the center of the foundation pit to the center of the existing station, B1 is the width of the newly built foundation pit, μ is the Poisson's ratio of the soil, d is the excavation depth of the foundation pit, τ is the shear stress, and L is the length of the foundation pit. Wherein, the coordinates of a point of the foundation pit are (f, y0, z0).

[0019] As a further technical solution, the reaction force caused by the additional stress transmitted by the existing structure is: F1=K x w; wherein, K x is the spring stiffness, β2 is the characteristic coefficient; A1, B2, C1, D1 are related coefficients of the general solution of the four-order constant coefficient non-homogeneous linear equation; and σ c is the additional stress.

[0020] ​As a further technical solution, the earth pressure σ1 of the first sliding body is:

[0021]

[0022] Where: when z = 0, σ Z When q is equal, m1 can be obtained. K a Rankine's active earth pressure coefficient q represents the ground overload, b represents the horizontal distance from the left edge of the station to the right edge of the pile, hj represents the distance from the ground to the upper surface of the station, θ represents the soil slip surface failure angle, and z represents the soil depth, with z ranging from 0 to h. j γ is the soil weight.

[0023]

[0024]

[0025] As a further technical solution, the earth pressure σ2 of the second sliding body is:

[0026]

[0027] in,

[0028]

[0029] K a Rankine's active earth pressure coefficient z represents the depth of the soil mass, and the range of values ​​for Z is h. j ~h j +h0+h s -btanθ; γ is the soil weight, F1 is the foundation reaction force generated by the additional stress of the existing structure, F1 = K x w is the friction angle δ1 between the soil and the retaining structure, δ2 is the friction angle δ2 between the soil and the existing station, b is the horizontal distance from the left edge of the station to the right edge of the pile, and h is the distance from the ground to the upper surface of the station. j θ is the failure angle of the soil slip surface.

[0030] As a further technical solution, the earth pressure σ3 of the third sliding body is:

[0031]

[0032] in,

[0033]

[0034] K a Rankine's active earth pressure coefficient H is the foundation pit depth, P is the distance from the bottom of the foundation pit to the bottom of the pile, z is the depth of the soil, the value range of z is h j +h0+h s -btantheta~h j +h0+h s ; gamma is the specific gravity of the soil, b is the distance from the left edge of the station to the right edge of the pile, the distance from the ground to the upper surface of the station is h j , the distance from the lower surface of the station to the bottom of the pile is hs, and the failure angle of the soil slip surface is theta.

[0035] The present application firstly collects relevant stratum parameters as basic parameters according to actual engineering projects. Then the position parameters of the existing structure and the newly-built foundation pit are determined, the stratum rupture surface of the foundation pit construction is determined, the additional stress transmitted by the existing structure is calculated, and in this process, the relevant stratum parameters and the corresponding soil slip surface failure angle, internal friction angle and the like are needed. Then the calculation formula of the earth pressure is derived through the thin layer element method, and finally the earth pressure is calculated by using the derived calculation formula.

[0036] The beneficial effects of the present application are as follows:

[0037] The present application can more specifically and accurately calculate the soil pressure condition and safety reserve condition of a point on the supporting side wall of the newly-built foundation pit. The previous calculation only considered the calculation of the earth pressure by the thin layer element, and then the force of the enclosure structure was obtained. The present application considers the influence of the additional stress generated by the foundation pit excavation on the existing structure, so that the existing structure will generate a corresponding ground reaction force. On the basis of the calculation of the thin layer element method, the calculation of the additional stress is more refined, and the key innovative step is to use the superposition operation of the two in the calculation step of the influence area of the existing structure. Unlike the previous additional stress influence generated by the existing structure, the present application more accurately calculates the size of the earth pressure of the newly-built foundation pit, is more in line with the actual stress condition, and improves the safety of the newly-built foundation pit. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is a schematic diagram of the overall technical scheme;

[0039] Figure 2 is the structure parameter of the existing structure and the newly-built foundation pit;

[0040] Figure 3 is a schematic diagram of the stratum rupture surface of the foundation pit construction;

[0041] Figure 4 is a schematic diagram of the Mindlin solution under the action of the concentrated force;

[0042] Figure 5 is a schematic diagram of the stratum of the foundation pit construction;

[0043] Figure 6is a schematic diagram of a thin layer unit analysis model;

[0044] Figure 7 is a schematic diagram of earth pressure calculation;

[0045] In the figure: 1. enclosure structure, 2. new foundation pit, 3. existing structure, 4. soil, 5. slip body ABCD, 6. ground overload, 7. slip body BEG'C', 8. slip body EFG, 9. support structure, 10. additional stress. DETAILED DESCRIPTION

[0046] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0047] It should be noted that the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit exemplary embodiments according to the present application. As used herein, the singular form is intended to include the plural form unless the context clearly indicates otherwise, and it should be understood that when the terms "comprise" and / or "include" are used in the specification, they indicate the presence of the features, steps, operations, devices, components and / or combinations thereof;

[0048] To solve the above technical problems, the embodiment provides a complete technical solution for calculating the earth pressure of a foundation pit near an existing underground structure. First, collect relevant stratum parameters as basic parameters according to actual engineering projects. Then determine the position parameters of the existing structure and the new foundation pit, determine the stratum fracture surface of the foundation pit construction, calculate the additional stress transmitted by the existing structure, and in this process, use the collected relevant stratum parameters and the corresponding soil slip surface failure angle, internal friction angle, etc. Then, through the thin layer element method, the calculation formula of the earth pressure is derived, and finally the earth pressure is calculated using the derived calculation formula.

[0049] The specific overall technical solution is shown in Figure 1 The specific process is as follows:

[0050] Step 1: Collect stratum parameters

[0051] Conduct site geological exploration for actual engineering projects to collect relevant stratum parameters, including the internal friction angle of the stratum soil and the specific gravity of the soil.

[0052] Step 2: Determine the structure parameters of the existing structure and the new foundation pit

[0053] The structure parameters of the existing structure and the new foundation pit are shown in Figure 2 The distance from the ground to the upper surface of the station h j, the distance between the lower surface of the station and the bottom of the pile h s , the distance between the left edge of the station and the right edge of the pile b, the length of the station b s , the depth of the foundation pit H, the distance between the bottom of the foundation pit and the bottom of the pile P.

[0054] Step 3: Determine the rupture surface of the foundation pit construction stratum

[0055] The determination of the rupture surface is based on the soil slip failure angle θ generated when the station is destroyed, where is the friction angle of the soil, and the distance between the ground and the upper surface of the station h j , the height of the station h0, the distance between the lower surface of the station and the bottom of the pile h s , the distance between the left edge of the station and the right edge of the pile b, the length of the station b When the conditions are met, the rupture surface of the foundation pit construction stratum is studied. The upper part of the existing structure extends along the failure angle θ to the ground, forming the slip surface of the slip body ABCD (a trapezoid), and the bottom of the retaining pile extends along the rupture angle θ to the lower part of the existing structure, forming the slip surface of the slip body EFG, where the slip body BEG'C' needs to consider the influence of additional stress, and the specific rupture surface is as follows Figure 3 The rupture surface of the foundation pit construction stratum is shown.

[0056] Step 4: Determine the additional stress transmitted by the existing structure

[0057] During the excavation of the foundation pit, the stress of the retaining structure will be affected by the additional stress generated by the existing structure. The additional stress of the existing structure will generate a certain foundation reaction on the newly built foundation pit, and the size of the earth pressure of the newly built foundation pit will be affected. Therefore, it is necessary to consider the additional stress generated by the existing structure, such as Figure 4 The Mindlin solution under concentrated force is shown in the figure. When a concentrated force Pv acts on a point (0, 0, -c) in the semi-infinite body, the additional principal stress at any point (x, y, z) in the semi-infinite body is:

[0058]

[0059] The horizontal unloading static earth pressure N = βK0γd and the basic stress solution of Mindlin load, R3, R4 are the distances from point (B1 / 2, η, τ) and point (B1 / 2, η, -τ) to the axis of the foundation pit (f, y0, z0). β1 is the stress loss rate of the foundation pit retaining structure, which is referred to the research of Jiang Zhaohua, and its value β1 = 0.75, K0 is the static earth pressure coefficient is the internal friction angle, γ is the specific weight of soil, f is the distance from the center of the existing station to the center of the new foundation pit, B1 is the width of the new foundation pit, μ is the Poisson's ratio of soil, d is the depth of the foundation pit, τ is the shear stress, L is the length of the foundation pit, and by integration, the horizontal additional stress of a point (f, y0, z0) of the foundation pit caused by the unit force βK0γπdηdτ of a point (η, τ) of the side wall of the foundation pit near the existing station is as follows:

[0060]

[0061] wherein The expression of the relationship between the deflection of the station and the horizontal additional stress is as follows:

[0062]

[0063] wherein:

[0064] E1 is the elastic modulus of the existing station (kN / m 2 ); I is the moment of inertia of the existing station (m 4 ); w is the deflection of the existing station (m); K x is the spring stiffness, which is an important parameter reflecting the interaction between soil and the existing station. w I is the horizontal bending stiffness of the retaining wall, h is the average vertical spacing of the support, γ w is the specific weight of water, and in order to further solve, the formula can be rewritten as follows:

[0065]

[0066] In order to simplify the formula, the parameters in the formula are as follows: wherein β2 is a characteristic coefficient, the dimension is m -1 ; E1 is the elastic modulus of the existing station (kN / m 2 ); I is the moment of inertia of the existing station (m 4 ); w is the deflection of the existing station (m); K x is the spring stiffness of each part, which is an important parameter reflecting the interaction between soil and the existing station. β2 is a comprehensive index related to the elastic properties of the beam and foundation, which can affect the stress and strain characteristics of the elastic foundation beam. A1, B2, C1 and D1 are related coefficients of the general solution of the fourth-order constant coefficient non-homogeneous linear equation, and after the characteristic coefficient is raised to the fourth power and substituted into the formula, the basic differential equation of the elastic foundation beam changes into the following form:

[0067]

[0068] The above formula is a fourth-order constant coefficient non-homogeneous linear equation, and its general solution can be obtained by solving:

[0069] ​

[0070] The ground reaction force caused by additional stress is:

[0071] F1 = K x w

[0072] Step 5: Calculate the earth pressure

[0073] The micro-element analysis is performed on the sliding body ABCD, as shown in Figure 5 , Figure 6 The internal friction angle of the soil is The specific weight of the soil is γ, the thickness of the thin layer micro-element is dz, the width of the upper surface of the thin layer micro-element is bs, the interface friction angle between the soil and the enclosure structure is δ1, the interface friction angle between the soil and the existing station is δ2, the vertical normal stress on the upper surface of the thin layer micro-element is σ z , the vertical normal stress increment on the lower surface of the thin layer micro-element is σz+dσ, σ x1 and τ1 are the horizontal normal stress and shear stress of the enclosure structure on the thin layer micro-element, respectively, and the shear stress value is σ x1 .tanδ1, T and τ are the normal stress and shear stress on the sliding surface, respectively, and the shear stress value is τ = c + T·tanθ, c is the cohesion of the soil, the self-weight of the thin layer micro-element is w, which is γ.A, A2 is the area of the micro-element, and q is the ground overload. a K is the Rankine active earth pressure coefficient. According to Figure Six The stress characteristics of the thin layer element are established by the thin layer element method, and the horizontal direction balance equation and the vertical balance equation are respectively:

[0074]

[0075] wherein: σ x1 = K a σ z , T = a1σ z +a2, By combining, we get: As shown in Figure 5 The ground stratum during the foundation pit construction, for the analysis of the sliding body ABCD, the depth of the sliding body ABCD is in the range of 0~h j , and the corresponding earth pressure σ1 is:

[0076]

[0077] wherein: when z = 0, σ Z =q, m1 is obtained, K a is the Rankine active earth pressure coefficient q is the ground overload, b is the distance from the left edge of the station to the right edge of the pile in the horizontal direction, h jh is the distance from ground to the upper surface of the station, θ is the failure angle of the soil slip surface, z is the depth of any point, γ is the unit weight of the soil, a1, a2, a3, a4 are the process coefficients required in the calculation process, and the above is solved.

[0078] For the analysis of the slip body BEG'C', the range of Z is h j ~ h j +h0+h s -btanθ, since the existing structure influences the soil slip, the additional stress of the existing structure will affect the earth pressure of the newly built foundation pit, and the additional stress of the existing structure will cause the ground reaction force of the soil on one side of the enclosure structure, so the additional stress of the structure should be considered in the calculation of the slip body BEG'C', and the influence of the newly built foundation pit should be calculated, so that σ2 is calculated as:

[0079]

[0080] wherein:

[0081]

[0082] K a is the Rankine active earth pressure coefficient z is the depth of the soil, γ is the unit weight of the soil, F1 is the ground reaction force caused by the additional stress of the existing structure F1=K x w, the friction angle δ1 between the soil and the enclosure structure, the friction angle δ2 between the soil and the existing station, b is the distance from the left edge of the station to the right edge of the pile in the horizontal direction, and h is the distance from the ground to the upper surface of the station j , the failure angle θ of the soil slip surface, a1, a2, a3, a4, a5 are the process coefficients required in the calculation process.

[0083] For the analysis of the slip body EFG, the range of z is h j +h0+h s -btanθ~h j +h0+h s , the stress σ3 can be obtained as:

[0084]

[0085] wherein:

[0086]

[0087] K a is the Rankine active earth pressure coefficient H is the depth of the foundation pit, P is the distance from the bottom of the foundation pit to the bottom of the pile, z is the depth of the soil, γ is the unit weight of the soil, b is the distance from the left edge of the station to the right edge of the pile in the horizontal direction, and h is the distance from the ground to the upper surface of the station j, the distance from the station lower surface to the pile bottom hs, the soil slip surface failure angle θ, a1a2a3a4a5 are process coefficients required in the calculation process, and the above is solved.

[0088] Example verification:

[0089] Taking a project as an example, the size of an existing station is 120*20*15m, the distance from the ground to the upper surface of the station h j＝ 13.14m, the distance from the left edge of the station to the right edge of the pile b=29.8m, the stratum is a silty clay stratum, the Poisson's ratio μ=0.35, the soil bulk density γ=17kN / m3, the foundation pit excavation height H=40m, the foundation pit length is 150m, the foundation pit width is 24m. The distance from the center of the foundation pit to the center of the existing station f=51.8m, the distance from the foundation pit ground to the pile bottom P=10m, the soil cohesion c=8kPa, the soil slip surface failure angle θ=51°, the soil and the surrounding structure interface friction angle δ1 is 15°, the internal friction angle Without ground overloading, the soil and the existing station interface friction angle δ2 is 20°, the stress loss rate of the foundation pit support structure β1=0.75, the elastic modulus of the existing station E1=2000MPa, the inertia moment of the existing station I=1*10 12 mm 4 , the horizontal bending stiffness of the support wall E w I=10000kN / m 2 , the vertical average spacing of the support is h=8m, the water bulk density is γ w =9.8kN / m3, and the calculation is as follows Figure 7 The soil pressure calculation is shown.

[0090] The present application determines the lateral open cut foundation pit excavation near the underground structure, determines the foundation pit construction stratum fracture surface, analyzes the additional stress influence generated by the existing structure, derives the corresponding soil pressure formula according to the thin layer element method, and considers the foundation reaction generated by the additional stress to calculate the soil pressure of the corresponding foundation pit construction stratum fracture surface.

[0091] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for calculating earth pressure of a foundation pit considering stress transmission near an existing underground structure, characterized by, As follows: Step 1 obtaining stratum parameters; Step 2 obtaining position parameters of existing structure and new foundation pit structure; Step 3 determining foundation pit construction stratum rupture surface and three sliding blocks according to position parameters of existing structure and new foundation pit structure and sliding failure angle; wherein: The earth pressure of the first sliding body Is: ； wherein: when , m1 is obtained, wherein m1 is an undetermined coefficient, , is the Rankine active earth pressure coefficient , q is the ground overload, b is the distance from the left edge of the station to the right edge of the pile in the horizontal direction, h j is the distance from the ground to the upper surface of the station, θ is the failure angle of the sliding surface of the soil, z is the depth of the soil at any point, is the unit weight of the soil, is the internal friction angle of the soil; c is the cohesion. ； ； ； ; Soil pressure of the second sliding body is: wherein m2 is a coefficient to be determined; is the Rankine active earth pressure coefficient ; z is in the range of ; is the unit weight of soil, F1 is the reaction force of the ground generated by the additional stress of the existing structure, wherein , is the friction angle between the soil and the enclosure structure, is the friction angle between the soil and the existing station, b is the distance from the left edge of the station to the right edge of the pile in the horizontal direction, h j is the distance from the ground to the upper surface of the station, θ is the failure angle of the soil slip surface; Soil pressure of third sliding body Is: wherein m3 is a coefficient to be determined; is the Rankine active earth pressure coefficient , H is the depth of the foundation pit, P is the distance from the bottom of the foundation pit to the bottom of the pile, and z is in the range of ; is the bulk density of the soil; b is the distance from the left edge of the station to the right edge of the pile in the horizontal direction, h j is the distance from the ground to the upper surface of the station, h s is the distance from the lower surface of the station to the bottom of the pile, θ is the failure angle of the soil slip surface; h0 is the height of the station; Step 4 determining additional stress transmitted by existing structure; Step 5 calculating soil pressure of each sliding block.

2. The method of claim 1, wherein the method is characterized by, In step 3, the determination method of the foundation pit construction stratum rupture surface is as follows: a slip failure angle of a soil mass generated when a station is destroyed θ , a distance h from the ground to an upper surface of the station j , a station height h0, a distance h s from a lower surface of the station to a pile bottom , a distance b from a left edge of the station in a horizontal direction to a right edge of the pile, when a condition of θ is satisfied, to determine a rupture surface generated in a stratum of a foundation pit construction; wherein , is an internal friction angle of the soil mass.

3. The method of claim 2, wherein the method is characterized by, According to the foundation pit construction stratum rupture surface, three sliding blocks are determined, the first sliding block is a sliding block at the top of the existing structure; the second sliding block is a sliding block formed between the side of the existing structure and the new foundation pit, and the third sliding block is a sliding block at the bottom of the existing structure.

4. The method of claim 3, wherein the method is characterized by, The sliding surface of the first sliding block is a point on the upper part of the existing structure extending to the ground surface along the failure angle θ.

5. The method of claim 3, wherein the method is characterized by, The sliding surface of the third sliding block is the bottom of the enclosure pile extending to a point on the lower part of the existing structure along the rupture angle θ, forming the sliding surface of the sliding block.

6. The method of claim 1, wherein the method is characterized by, In step 4, the additional stress transmitted by the existing structure is: wherein, is the stress loss rate of the foundation pit retaining structure, is the static earth pressure coefficient , is the internal friction angle, γ is the specific weight of the soil, f is the distance from the center of the foundation pit to the center of the existing station, B1 is the width of the newly built foundation pit, μ is the Poisson's ratio of the soil, d is the excavation depth of the foundation pit, τ is the shear stress, and L is the length of the foundation pit. ； ； Wherein, the coordinates of a point in the foundation pit are (f, y0, z0); the coordinates of a point near the side wall of the existing station foundation pit are (η, τ).

7. The method of claim 6, wherein the method is characterized by, The counterforce caused by the additional stress transmitted by the existing structure is: ; wherein, ; is the spring stiffness, is the characteristic coefficient; A1, B2, C1, D1 are the related coefficients of the general solution of the four-order non-homogeneous linear equation; is the additional stress; wherein x represents the deflection value of the existing station.

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