A time-effect analysis method for ground surface settlement induced by foundation pit excavation in soft clay area

Abstract

The present application relates to the field of ground settlement prediction, and provides a time effect analysis method for ground settlement induced by foundation pit excavation in soft clay area, comprising: determining the time required for foundation pit construction under all working conditions and the retaining wall side displacement curve; determining the soil parameters according to the Boltzmann viscoelastic foundation model; obtaining the viscous settlement of all working conditions by using the Boltzmann viscoelastic foundation model; setting t=0 and the boundary condition as the retaining wall side displacement curve of all working conditions to obtain the elastic settlement under different working conditions; setting the boundary condition as the retaining wall side displacement curve when the bottom plate strength is formed to obtain the viscous settlement of the soil outside the pit after the bottom plate strength is formed; and summing the elastic and viscous settlement to obtain the ground settlement of the to-be-solved arbitrary working condition. The present application overcomes the problem that the existing theoretical method cannot consider the time effect of the soil, thereby leading to the problem that the prediction of the ground settlement is not safe, and also considers the ground settlement after the bottom plate strength is formed without depending on the retaining wall side displacement, which is more engineering significant and has good popularization and application value.

Description

Technical Field

[0001] This invention relates to the field of surface settlement prediction, and in particular to a time-dependent analysis method for surface settlement induced by foundation pit excavation in soft clay areas. Background Technology

[0002] With the vigorous development of urban construction activities, the demand for land resources in cities is increasing daily, and more and more foundation pit projects are located adjacent to buildings, subway stations, underground pipelines, etc. Foundation pit construction along subway tunnels is unavoidable. Excavation of foundation pits in soft soil areas with dense buildings and pipelines will inevitably disturb the surrounding environment, causing uneven road surface settlement, deformation of underground pipelines, and in severe cases, even structural cracking and damage. Therefore, accurately analyzing the surface settlement induced by foundation pit excavation is of significant practical importance.

[0003] Regarding theoretical research on surface settlement induced by foundation pit excavation, current technology considers that surface settlement is only related to the form and magnitude of the lateral displacement of the retaining wall, and is independent of the properties of the soil. The maximum surface settlement δ is given as... vm With the maximum lateral displacement δ of the retaining wall hm The relationship between them is δ. vm / δ hm ≈0.4. However, the Shanghai foundation pit code gives δ based on measured data. vm / δ hm The average value is 0.81. This is because the deformation and strength of soft clay change significantly over time, inducing settlement of the soil outside the pit that is independent of the lateral displacement of the retaining wall. However, existing theoretical solutions do not consider the creep of soft clay, i.e., viscous deformation. Therefore, a time-dependent analysis method for surface settlement induced by foundation pit excavation in soft clay areas is essential. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a time-dependent analysis method for surface settlement induced by foundation pit excavation in soft clay areas, addressing the problems in the background art.

[0005] Therefore, the technical solution adopted by the present invention is as follows:

[0006] This invention provides a time-dependent analysis method for surface settlement induced by foundation pit excavation in soft clay areas, the method comprising:

[0007] (1) Determine the time required for foundation pit construction and the lateral displacement curve of retaining wall under all working conditions;

[0008] (2) Determine soil parameters based on the Boltzmann viscoelastic foundation model;

[0009] (3) The viscous settlement under all working conditions was obtained using the Boltzmann viscoelastic foundation model;

[0010] (4) Let t = 0, and the boundary conditions are the retaining wall lateral displacement curves for all working conditions. Then, the elastic settlement under different working conditions is obtained.

[0011] (5) Set the boundary conditions to the lateral displacement curve of the retaining wall when the bottom plate strength is formed, and obtain the cohesive settlement of the soil outside the pit after the bottom plate strength is formed.

[0012] (6) The surface settlement for any working condition is obtained by summing the elastic and viscous settlements.

[0013] Furthermore, in step (1), the construction time required is obtained from the construction log or construction plan;

[0014] The retaining wall lateral displacement curve is the lateral displacement curve when the pit bottom support or the bottom plate has formed strength. It is obtained by using existing formulas (or polynomial fitting) and empirical formulas for the maximum lateral displacement of the retaining wall (or measured lateral displacement of the retaining wall).

[0015] Furthermore, the earthwork excavation and the strength of the support or base slab are summarized into a single working condition.

[0016] Furthermore, the soil parameters include bulk modulus K, shear modulus G. l K-body shear modulus G k and viscosity coefficient η k .

[0017] Furthermore, the bulk modulus K and the bulk shear modulus G l The expression is:

[0018]

[0019] Where E is the elastic modulus of the soil, which can be approximated as 2.5 to 3.5 times the compression modulus of the soil; v is the Poisson's ratio of the soil.

[0020] Furthermore, the shear modulus G of K body k and viscosity coefficient η k Obtained by time-related indoor compression tests, including but not limited to consolidation tests.

[0021] Furthermore, the specific steps of step (3) are as follows:

[0022] The time-dependent solution w for the surface settlement outside the pit induced by the lateral displacement of the retaining wall is derived using the Boltzmann viscoelastic foundation model. The expression is as follows:

[0023]

[0024] Where β=(1-v 2 ) / E;

[0025] v and E are Poisson's ratio and elastic modulus of the soil, respectively; β at different times in the viscoelastic foundation model can be represented by Equation 3.

[0026]

[0027] x is the distance from the point to the retaining wall, β0 is β at t=0; the lateral displacement curve of the retaining wall is divided into i micro-segments, i≥2; f1 is the lateral displacement of the top micro-segment of the wall; H1 is the height of the top micro-segment of the wall; f i For the lateral displacement of the i-th micro-segment; H i and H i-1 , respectively, are the distances from the bottom of the i-th and i-1-th micro-segments to the top of the wall;

[0028] Assume the retaining wall lateral displacement curve at the point where the j-th layer of earthwork excavation is completed and the supports or base slab have reached sufficient strength is f(z). j The time for the excavation, support, or foundation slab of the j-th layer of soil to develop strength is t. j , then t j Surface viscous settlement during the time period w cj The expression is:

[0029]

[0030] When the excavation of the m-th layer of soil is completed and the supports or base slab have reached sufficient strength, the total surface cohesive settlement w c The expression is:

[0031]

[0032] Assuming the total excavation volume of the foundation pit is p layers, let m = p. In this case, the above formula represents the surface cohesive settlement during the entire excavation stage.

[0033] Furthermore, the boundary condition in step (4) is the retaining wall lateral displacement curve when the m-th layer of earthwork excavation is completed and the support or base plate has reached strength. Let t = 0 in the time-dependent solution, and substitute it into Equation 2 to obtain the surface elastic settlement w under different working conditions. e The expression is:

[0034]

[0035] Let m = p, which represents the elastic settlement of the ground surface during the entire excavation stage.

[0036] Furthermore, by setting the boundary condition of the aging solution to the lateral displacement curve of the retaining wall when the base plate reaches its strength, the t value after the base plate reaches its strength is obtained. a Cohesive settlement of soil outside the pit over time w a The expression is:

[0037]

[0038] Furthermore, the surface settlement outside the pit under any working condition during the excavation phase and at any time after the excavation is completed is w. t They are represented as follows:

[0039]

[0040] The beneficial effects of this invention are:

[0041] This invention provides a time-effect analysis method for surface settlement induced by foundation pit excavation in soft clay areas. It overcomes the problem that existing theoretical methods cannot consider the time effect of soil, which leads to unsafe predictions of surface settlement. It also considers surface settlement after the foundation slab has formed, independent of the lateral displacement of the retaining wall, which is more significant in engineering and has great potential for widespread application. Attached Figure Description

[0042] Figure 1 This is a flowchart of the time-effect analysis method of the present invention.

[0043] Figure 2 This is a comparison chart of the fitted value and the measured value of the retaining wall lateral displacement in the embodiment, where s represents the retaining wall lateral displacement.

[0044] Figure 3 This is a schematic diagram of the Boltzmann viscoelastic foundation model.

[0045] Figure 4 A schematic diagram illustrating the equivalent calculation of surface settlement induced by the lateral displacement of a retaining wall segment.

[0046] Figure 5 This is a comparison chart of the calculated and measured values ​​of surface subsidence in the embodiments. Detailed Implementation

[0047] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. It should be noted that the embodiments are only specific descriptions of the present invention and should not be regarded as limitations on the present invention.

[0048] like Figure 1 As shown, this invention provides a time-dependent analysis method for surface settlement induced by foundation pit excavation in soft clay areas. The method includes:

[0049] S1, determine the construction time required for the foundation pit and the lateral displacement curve of the retaining wall under all working conditions; the construction time required is obtained from the construction log or construction plan; the lateral displacement curve of the retaining wall is the lateral displacement curve when the bottom support or bottom slab reaches strength, obtained using existing formulas (or polynomial fitting) and empirical formulas for the maximum lateral displacement of the retaining wall (or measured lateral displacement of the retaining wall). In addition, the earthwork excavation and the strength formation of the support or bottom slab are summarized into one working condition.

[0050] S2, determine soil parameters based on the Boltzmann viscoelastic foundation model;

[0051] The soil parameters include bulk modulus K and shear modulus G. l K-body shear modulus G k and viscosity coefficient η k .

[0052] Bulk modulus K and volume shear modulus G l The expression is:

[0053]

[0054] Where E is the elastic modulus of the soil, which can be approximated as 2.5 to 3.5 times the compression modulus of the soil; v is the Poisson's ratio of the soil.

[0055] K-body shear modulus G k and viscosity coefficient η k Obtained from time-related indoor tests, including but not limited to consolidation tests.

[0056] S3, the viscous settlement for all working conditions was obtained using the Boltzmann viscoelastic foundation model;

[0057] The specific steps are as follows:

[0058] The time-dependent solution w for the surface settlement outside the pit induced by the lateral displacement of the retaining wall is derived using the Boltzmann viscoelastic foundation model. The expression is as follows:

[0059]

[0060] Where β=(1-v 2 ) / E;

[0061] v and E are Poisson's ratio and elastic modulus of the soil, respectively; β at different times in the viscoelastic foundation model can be represented by Equation 3.

[0062]

[0063] x is the distance from the point to the retaining wall, β0 is β at t=0; the lateral displacement curve of the retaining wall is divided into i micro-segments, i≥2; f1 is the lateral displacement of the top micro-segment of the wall; H1 is the height of the top micro-segment of the wall; f i For the lateral displacement of the i-th micro-segment; H i and H i-1 , respectively, are the distances from the bottom of the i-th and i-1-th micro-segments to the top of the wall;

[0064] Assume the retaining wall lateral displacement curve at the point where the j-th layer of earthwork excavation is completed and the supports or base slab have reached sufficient strength is f(z). j The time for the excavation, support, or foundation slab of the j-th layer of soil to develop strength is t. j , then t jSurface viscous settlement during the time period w cj The expression is:

[0065]

[0066] When the excavation of the m-th layer of soil is completed and the supports or base slab have reached sufficient strength, the total surface cohesive settlement w c The expression is:

[0067]

[0068] Assuming the total excavation volume of the foundation pit is p layers, let m = p. In this case, the above formula represents the surface cohesive settlement during the entire excavation stage.

[0069] S4, let t=0, with the boundary conditions being the retaining wall lateral displacement curves for all working conditions, and obtain the elastic settlement w under different working conditions. e ;

[0070] Specifically, let the boundary condition be the retaining wall lateral displacement curve when the m-th layer of earthwork excavation is completed and the support or base plate has reached strength, and let t=0 in the time-dependent solution. Substitute these values ​​into Equation 2 to obtain the elastic settlement w of the ground surface under different working conditions. e The expression is:

[0071]

[0072] Let m = p, which represents the elastic settlement of the ground surface during the entire excavation stage.

[0073] S5, setting the boundary condition to the retaining wall lateral displacement curve at the time of base plate strength formation, obtains the base plate strength formation t. a Cohesive settlement of the soil outside the pit after time w a The expression is:

[0074]

[0075] S6, summing the elastic and viscous settlements yields the surface settlement for any given working condition, including the surface settlement outside the pit w for any working condition during the excavation stage and at any time after excavation. t They are represented as follows:

[0076]

[0077] Example

[0078] S1: The earthwork excavation and the strength formation of the support or base slab are summarized into a working condition, and the time of each working condition is determined by the construction log; in the example, there are six working conditions for the foundation pit, with time periods of 31 days, 37 days, 43 days, 32 days, 31 days and 57 days respectively.

[0079] The lateral displacement curve of the retaining wall is obtained using measured data and existing formulas, and the expression is as follows:

[0080]

[0081] Among them, the maximum lateral displacement f of the retaining wall under six working conditions max The depth H of the retaining wall where the maximum lateral displacement occurred was 9.8, 44.1, 63.8, 89.9, 109.7, and 142.6 mm respectively. m The excavation depths H of the retaining wall under the six working conditions are 11.5, 12.5, 15.5, 20.0, 24.0, and 24.5 m, respectively; the pit excavation depths H are 8.3, 13.8, 17.9, 22.1, 26.3, and 30.2 m, respectively; and the pit embedment depths are 41.7, 36.2, 32.1, 27.9, 23.7, and 19.8 m, respectively. The lateral displacement curves of the retaining wall under these six working conditions can be expressed as f(z). 1～6 ;like Figure 2 The figure shows a comparison between the fitted value and the measured value of the retaining wall lateral displacement in the embodiment. The fitted value and the measured value are basically consistent, which verifies the accuracy of the fitted value of the retaining wall lateral displacement.

[0082] S2: Determine soil parameters based on the Boltzmann viscoelastic foundation model, such as... Figure 3 As shown, the soil parameters include the bulk modulus K and the shear modulus G. l The expression is as follows:

[0083]

[0084] Where E is taken as 3 times the soil compression modulus; after weighted averaging of the soft soil layer parameters, E is 10 MPa and v is 0.4.

[0085] The calculated bulk modulus K is 16.7 MPa, and the bulk shear modulus G is... l It is 3.6 MPa.

[0086] K-body shear modulus G k and viscosity coefficient η k The values ​​are 0.8 MPa and 200 MPa per day, respectively.

[0087] S3: As Figure 4 The diagram shows the equivalent calculation of surface settlement induced by the lateral displacement of a retaining wall segment. The time-dependent solution w for the surface settlement outside the pit induced by the lateral displacement of the retaining wall is derived using the Boltzmann viscoelastic foundation model, as shown below:

[0088]

[0089] in,

[0090]

[0091] x is the distance from the point to the retaining wall, β0 is β at t=0; the lateral displacement curve of the retaining wall is divided into 50 micro-segments of 1m each, f1 is the lateral displacement of the top micro-segment, H1 is the height of the top micro-segment, f i For the lateral displacement of the i-th micro-segment, H i and H i-1 These are the distances from the bottom of the i-th and i-1th micro-segments to the top of the wall, respectively.

[0092] Surface viscous settlement under different working conditions can be expressed as:

[0093]

[0094] The start and end times for the six operating conditions are 0–30, 30–67, 67–110, 110–142, 142–173, and 173–230 days, respectively.

[0095] When the excavation of the m-th layer of soil is completed and the supports or base plate have reached sufficient strength, the total surface cohesive settlement can be expressed as:

[0096]

[0097] S4: Setting t=0 for the time-dependent solution, and using the retaining wall lateral displacement curves at the completion of the m-th layer of earthwork excavation and the formation of strength of the support or base slab as boundary conditions, the elastic settlement of the ground surface under different working conditions can be obtained, as expressed below:

[0098]

[0099] S5: Let the boundary condition of the aging solution be the lateral displacement curve of the retaining wall when the bottom plate strength is formed, and obtain the viscous settlement when the surface settlement outside the pit converges. The expression is as follows:

[0100]

[0101] S6: Surface settlement is the sum of elastic and viscous settlement. The surface settlement outside the pit under any working condition during the excavation stage and at any time after the excavation is completed can be expressed as follows:

[0102]

[0103] like Figure 5 As shown, the comparison between the calculated and measured values ​​of surface settlement in the embodiment shows that the calculated and measured values ​​are in excellent agreement, indicating that the method effectively reflects the actual state of the soil outside the construction pit. This demonstrates that the method presented in this paper can be used for the calculation and analysis of surface settlement induced by the excavation of deep soft clay foundation pits. Furthermore, the method is simple and practical, and has significant engineering implications for evaluating the environmental effects of foundation pits.

[0104] It should be noted that any technical features not described in detail in this invention can be implemented using any existing technology.

[0105] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

Claims

1. A time-dependent analysis method for surface settlement induced by foundation pit excavation in soft clay areas, characterized in that, The method includes: (1) Determine the time required for foundation pit construction and the lateral displacement curve of retaining wall under all working conditions; (2) Determine soil parameters based on the Boltzmann viscoelastic foundation model; the soil parameters include bulk modulus K and shear modulus G. l K-body shear modulus G k and viscosity coefficient η k ; (3) The viscous settlement under all working conditions was obtained using the Boltzmann viscoelastic foundation model; The specific steps are as follows: The time-dependent solution for surface settlement outside the pit induced by retaining wall displacement was derived using the Boltzmann viscoelastic foundation model. The expression is: Formula 2; in, Formula 3 x is the distance from the point to the retaining wall, β0 is β at t=0; divide the lateral displacement curve of the retaining wall into i micro-segments, i≥2; f1 is the lateral displacement of the top micro-segment of the wall; H1 is the height of the top micro-segment of the wall; f i For the lateral displacement of the i-th micro-segment; H i and H i-1 , respectively, are the distances from the bottom of the i-th and i-1-th micro-segments to the top of the wall; Assume the retaining wall lateral displacement curve at the point where the j-th layer of earthwork excavation is completed and the supports or base slab have reached sufficient strength is f(z). j The time for the excavation, support, or foundation slab of the j-th layer of soil to develop strength is t. j , then t j Surface viscous settlement during the time period The expression is: Equation 4; When the excavation of the m-th layer of soil is completed and the supports or base plate have reached sufficient strength, the total surface cohesive settlement... The expression is: Formula 5; Assuming the total excavation volume of the foundation pit is p layers, let m = p. In this case, the above formula represents the surface cohesive settlement during the entire excavation stage. (4) Let t=0, and the boundary conditions are the retaining wall lateral displacement curves for all working conditions. Then, the elastic settlement under different working conditions is obtained. (5) Set the boundary conditions to the lateral displacement curve of the retaining wall when the bottom plate strength is formed, and obtain the cohesive settlement of the soil outside the pit after the bottom plate strength is formed. (6) The surface settlement for any working condition is obtained by summing the elastic and viscous settlements.

2. The time-dependent analysis method for surface settlement induced by foundation pit excavation in soft clay areas according to claim 1, characterized in that, In step (1), the construction time required is obtained from the construction log or construction plan; The lateral displacement curve of the retaining wall is the lateral displacement curve when the pit bottom support or the bottom plate has reached strength.

3. The time-dependent analysis method for surface settlement induced by foundation pit excavation in soft clay areas according to claim 1, characterized in that, The earthwork excavation and the strength of the support or base slab are summarized into one working condition.

4. The time-dependent analysis method for surface settlement induced by foundation pit excavation in soft clay areas according to claim 1, characterized in that, Bulk modulus K and volume shear modulus G l The expression is: Formula 1; Where E is the elastic modulus of the soil; v is the Poisson's ratio of the soil.

5. The time-dependent analysis method for surface settlement induced by foundation pit excavation in soft clay areas according to claim 1, characterized in that, K-body shear modulus G k and viscosity coefficient η k It was obtained from time-related indoor compression tests.

6. The time-dependent analysis method for surface settlement induced by foundation pit excavation in soft clay areas according to claim 1, characterized in that, The boundary condition in step (4) is the retaining wall lateral displacement curve when the m-th layer of earthwork excavation is completed and the support or base plate has reached strength. Let t=0 in the time-dependent solution and substitute it into Equation 2 to obtain the elastic settlement of the ground surface under different working conditions. The expression is: Formula 6; Let m = p, which represents the elastic settlement of the ground surface during the entire excavation stage.

7. The time-dependent analysis method for surface settlement induced by foundation pit excavation in soft clay areas according to claim 6, characterized in that, Let the boundary condition of the aging solution be the lateral displacement curve of the retaining wall when the base plate reaches its strength, and then calculate t after the base plate reaches its strength. a Cohesive settlement of soil outside the pit over time The expression is: Formula 7.

8. The time-dependent analysis method for surface settlement induced by foundation pit excavation in soft clay areas according to claim 7, characterized in that, Ground surface settlement outside the pit under any working condition during the excavation phase and at any time after the excavation is completed. They are represented as follows: Formula 8.

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