Method for calculating and evaluating lateral pressure of support structure considering change of pore pressure

Abstract

This invention provides a method for calculating and evaluating the impact of lateral pressure on a support structure considering pore pressure variations. The calculation method includes the following steps: establishing a coordinate system with a point on the seabed surface as the origin, the direction towards the pit as the positive X-axis, and the vertical upward direction as the positive z-axis; and calculating the lateral pressure σ at any point on the active side of the support structure under wave load based on formulas (1), (2), and (3). t1 (z) and the lateral pressure σ at any point on the passive side of the support structure is calculated based on formula (4). t2 (z); Based on formulas (1) to (3), integration is performed along the depth direction to obtain the active lateral pressure E of the support structure under wave load. a,t Based on formula (4), the passive lateral pressure E of the support structure under wave load is obtained by integrating along the depth direction. p,t .

Description

Technical Field

[0001] This invention belongs to the field of foundation pit engineering technology, and in particular relates to a method for calculating and evaluating the impact of lateral pressure on support structures that takes into account changes in pore pressure. Background Technology

[0002] With the rapid development of underground space, the implementation of major projects such as cross-sea tunnels, cross-sea bridges, large wharves, and cruise ship homeports has led to an increase in the number of foundation pit projects, which are also expanding in size and depth. On the other hand, the rapid development of the national economy and tourism industry has resulted in the continuous emergence of new resorts and hotels along the coast and waterfront, requiring the full utilization and development of underground space. Consequently, a large number of foundation pits near rivers or the sea have also appeared. These foundation pits are often in contact with water or close to water bodies, with complex hydrogeological conditions. They are frequently affected by tides, sediment, and waves, and have ample water supply. The impact of dynamic water seepage on deep and large foundation pits is even more significant.

[0003] Currently, relevant standards and literature only consider lateral soil and water pressure in the stress calculation of foundation pit support structures, without considering the additional effect of changes in soil pore water pressure under water level fluctuations or wave loads on the foundation pit support structure. However, the additional load on foundation pits with large water level fluctuations or direct wave loads cannot be ignored. Therefore, determining whether changes in soil pore water pressure under water level fluctuations or wave loads affect the foundation pit support structure, and accurately calculating the load on the foundation pit support structure under changes in soil pore water pressure, is of great significance for the safety control of foundation pits near rivers and coasts. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art by providing a method for calculating and evaluating the lateral pressure of a support structure that considers changes in pore pressure.

[0005] This invention is achieved through the following technical solution:

[0006] A method for calculating the lateral pressure of a support structure considering pore pressure variations includes the following steps:

[0007] Establish a coordinate system with a point on the seabed surface as the origin, the direction towards the pit as the positive X-axis, and the vertical upward direction as the positive z-axis;

[0008] Calculate the lateral pressure σ at any point on the active side of the support structure under wave load. t1 (z) and the lateral pressure σ at any point on the passive side of the support structure. t2 (z), where the calculation formula is as follows:

[0009]

[0010]

[0011]

[0012]

[0013] In the formula, γ0 is the natural unit weight of the seabed soil cover layer, γ 0sat γ is the saturated unit weight of the seabed soil cap layer, and γ is the natural unit weight of the seabed soil. sat The saturated unit weight of the seabed soil. ω is the wave number, z is the position of the calculation point, h3 is the distance between the top of the support structure and the seabed surface, and b is the thickness from the bottom of the support structure to the bottom of the calculated seabed soil layer.

[0014] Based on equations (1) to (3), integration along the depth direction yields the active lateral pressure E of the support structure under wave load. a，t Based on formula (4), the passive lateral pressure E of the support structure under wave load is obtained by integrating along the depth direction. p，t :

[0015] E a，t =∑σ t1 (z)*h (5)

[0016] E p,t =∑σ t2 (z)*h (6)

[0017] In the formula, h is the thickness at the calculation point.

[0018] This invention also proposes a method for evaluating the lateral pressure influence of support structures considering pore pressure variations, comprising the following steps:

[0019] Using the above-mentioned method for calculating the lateral pressure of the support structure considering pore pressure variation, the active side lateral pressure and passive side lateral pressure of the support structure under wave load are calculated.

[0020] Based on the lateral pressure on the active side of the support structure and the lateral pressure on the passive side of the support structure, a first evaluation index characterizing the impact of wave load on the pressure of the support structure of the foundation pit is calculated. The first ratio is obtained by calculating the ratio of the change amplitude of the difference between the active side lateral pressure and the active side lateral pressure of the support structure to the difference in earth pressure before the wave load. The first evaluation index includes relative active earth pressure and relative passive earth pressure. The relative active earth pressure is the ratio of the change amplitude of the active side lateral pressure of the support structure before and after the wave load to the active side lateral pressure of the support structure before the wave load. The relative passive earth pressure is the ratio of the change amplitude of the passive side lateral pressure of the support structure before and after the wave load to the passive side lateral pressure of the support structure before the wave load.

[0021] Determine the boundary conditions of the theoretical model of the foundation pit;

[0022] Based on boundary conditions, a second evaluation index characterizing the influence of wave load on the change of excess pore pressure in soil is calculated. The second evaluation index includes a second ratio, which is the ratio of the change amplitude of total pore water pressure at the calculation point to the change amplitude of wave water pressure.

[0023] Determine whether both the first evaluation index and the second evaluation index are less than a preset first threshold, and determine whether the first ratio is less than a preset second threshold;

[0024] If yes, then the wave load has no effect on the pressure of the support structure; if no, then the wave load has an effect on the pressure of the foundation pit support structure.

[0025] Furthermore, the steps for determining the boundary conditions of the foundation pit theoretical model include:

[0026] (1) Determine the bottom boundary conditions. When the seabed depth is finite, the bottom of the theoretical model is an impermeable boundary, satisfying:

[0027]

[0028] In the formula, z represents the depth below the seabed surface, and P t (z) represents the total pore water pressure at time t;

[0029] (2) Determine the right-side boundary conditions. The right-side boundary is the central axis of symmetry of the foundation pit and is assumed to be an impermeable boundary, satisfying the following:

[0030]

[0031] In the formula, P t (z) represents the total pore water pressure caused by wave action at time t;

[0032] (3) Determine the left boundary conditions. When the calculation point is in the seabed soil, it satisfies formula (9). When the calculation point is in the water, it satisfies formula (10).

[0033]

[0034]

[0035] In the formula, γ w Where is the specific weight of water, and H is the wave height. ω is the wave number, d is the still water level depth, k is the soil permeability coefficient, and z is the bottom of the foundation pit.

[0036] (4) Determine the boundary conditions at the bottom of the foundation pit. Assume the water level is at the bottom of the foundation pit and satisfies the following conditions:

[0037] Pc t (z)=0 (11)

[0038] In the formula, Pc t (z) represents the excess pore water pressure at time t;

[0039] (5) Determine the boundary conditions of the water-stop curtain. Assume that the water-stop curtain is impermeable and satisfies the following:

[0040]

[0041] (6) Determine the seabed surface boundary conditions, where the groundwater level fluctuation is directly applied to the horizontal surface of the soil layer at z = d via pore pressure, satisfying:

[0042]

[0043] In the formula, Pc t (z) represents the excess pore water pressure at any point t on the seabed surface;

[0044] The wave pressure applied to the surface of the seabed soil is:

[0045]

[0046] In the formula, p b This represents the maximum wave pressure acting on the surface of the seabed soil.

[0047] Furthermore, based on boundary conditions, the steps for calculating the second evaluation index characterizing the influence of wave load on soil excess pore pressure variation include:

[0048] If the calculation point is below the seabed, the second evaluation index is calculated using formula (15); if the calculation point is above the seabed, the second evaluation index is calculated using formula (16).

[0049]

[0050]

[0051] In the formula, P t，max (z) represents the maximum value of the total pore water pressure under the boundary conditions. γ is the average of all total pore water pressures under the boundary conditions. w It is the density of water.

[0052] Furthermore, based on the active and passive lateral pressures of the support structure, the steps for calculating the first evaluation index characterizing the impact of wave loads on the pressure of the support structure in the foundation pit include:

[0053] Calculate the relative active earth pressure δE using the following formula. a and relative passive earth pressure δE p :

[0054]

[0055]

[0056] In the formula, △E a E represents the amplitude of the change in lateral pressure on the active side of the support structure before and after wave loading. a，tmax E represents the maximum value of the active lateral pressure on the support structure after wave loading. a，tmin E represents the minimum lateral pressure on the active side of the support structure after wave loading. a,0 The active lateral pressure on the support structure before wave load is applied, ΔE p E represents the amplitude of the change in passive lateral pressure on the support structure before and after wave loading. p，tmax The maximum value of the passive lateral pressure on the support structure after wave loading, E p，tmin The minimum passive lateral pressure on the support structure after wave loading, E p，0 The passive lateral pressure on the support structure before wave load.

[0057] Further, the steps to calculate the first ratio by comparing the change in the difference between the active lateral pressure and the passive lateral pressure of the support structure with the difference in earth pressure before the wave load are applied include:

[0058] The first ratio is calculated using the following formula:

[0059]

[0060] △E a-p =max{|(E a，t -E p，t ) max -(Ea，t -E p，t )0|,|(E a，t -E p，t ) min -(E a，t -E p，t )0|}(18)

[0061] In the formula, △E a-p E represents the amplitude of the difference between the lateral pressure on the active side and the lateral pressure on the passive side of the support structure after wave loading. a，t -E p，t )0 represents the difference between the lateral pressure on the active side and the lateral pressure on the passive side of the support structure before wave loading. Ex ，t E represents the active lateral pressure on the support structure after wave load application. p，t The passive lateral pressure on the support structure after wave load.

[0062] Furthermore, the preset first threshold is 10%, and the preset second threshold is 5%.

[0063] Compared with existing technologies, the beneficial effects of this invention are as follows: It proposes a method for calculating and evaluating the degree of influence of the lateral pressure on the active side and the passive side of the support structure caused by changes in soil pore water pressure under water level fluctuations or wave loads. This solves the problem of the lack of methods for determining the value of external dynamic water load under river and coastal conditions in the current field of foundation pit support structure design, improves the design theory of foundation pit support structures, and is of great significance for the rational design and safety control of deep foundation pits. Attached Figure Description

[0064] Figure 1 The flowchart illustrates the steps of the method for calculating the lateral pressure of a support structure considering pore pressure variations according to the present invention.

[0065] Figure 2 This is a schematic diagram of the calculation section for the lateral pressure calculation method of the support structure considering pore pressure variation according to the present invention.

[0066] Figure 3 This is a flowchart illustrating the steps of the method for evaluating the lateral pressure influence of support structures considering pore pressure variations, as presented in this invention.

[0067] In the diagram, 1-seabed, 2-foundation pit, 3-support structure, 4-water Detailed Implementation

[0068] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0069] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0070] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0071] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0072] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed when in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0073] Please see Figure 1 and Figure 2 , Figure 1 This is a flowchart illustrating the steps of the method for calculating the lateral pressure of a support structure considering pore pressure variations according to the present invention. Figure 2 This is a schematic cross-sectional view of the calculation method for the lateral pressure of a support structure considering pore pressure variations according to the present invention. A method for calculating the lateral pressure of a support structure considering pore pressure variations includes the following steps:

[0074] S11. Establish a coordinate system with a point on the seabed surface as the origin, the direction towards the pit as the positive x-axis, and the vertical upward direction as the positive z-axis.

[0075] S12. Calculate the lateral pressure σ at any point on the active side of the support structure under wave load. t1 (z) and the lateral pressure σ at any point on the passive side of the support structure. t2 (z), where the calculation formula is as follows:

[0076]

[0077]

[0078]

[0079]

[0080] In the formula, γ0 is the natural unit weight of the seabed soil cover layer, γ 0sat γ is the saturated unit weight of the seabed soil cap layer, and γ is the natural unit weight of the seabed soil. sat The saturated unit weight of the seabed soil. ω is the wave number, z is the position of the calculation point, h3 is the distance between the top of the support structure and the seabed surface, and b is the thickness from the bottom of the support structure to the bottom of the calculated seabed soil layer.

[0081] S13. Based on formulas (1) to (3), integrate along the depth direction to obtain the active lateral pressure E of the support structure under wave load. a，t Based on formula (4), the passive lateral pressure E of the support structure under wave load is obtained by integrating along the depth direction. p，t :

[0082] E a，t =∑σ t1 (z)*h (5)

[0083] E p，t =∑σ t2 (z)*h (6)

[0084] In the formula, h is the thickness at the calculation point.

[0085] In step S11 above, the coordinate system XOZ is established as follows: Figure 2 As shown, in Figure 2In the diagram, point d on the seabed surface is taken as the origin, the vertical upward direction is the positive z-axis, and the rightward direction (towards the excavation pit) is the positive x-axis. d represents the water depth outside the excavation pit, h1 represents the calculated thickness of the seabed soil, h2 represents the thickness of the remaining soil after the excavation pit, h3 represents the thickness of the support structure above the seabed surface, b represents the thickness from the bottom of the support structure to the bottom of the calculated seabed soil layer, a1 represents the width of the calculated soil layer outside the pit, and a2 represents the width of the calculated soil layer inside the pit.

[0086] In step S12 above, the active side of the support structure is the outer side of the support structure, that is, the side of the support structure away from the foundation pit, and the passive side of the support structure is the inner side of the support structure, that is, the side of the support structure facing the center of the foundation pit. Since the active side of the support structure is in contact with the water and soil, and because waves cause water level fluctuations, the lateral pressure on different parts of the active side of the support structure will be different. On the active side of the support structure, if the calculation point is within the range from the top of the support structure to the water surface, i.e. Then, formula (1) is used to calculate the lateral pressure at the calculation point. If the calculation point is located between the water surface and the seabed surface, i.e. The lateral pressure at the calculation point is calculated using formula (2). If the calculation point is located between the seabed surface and the bottom of the support structure, i.e., -(h1-b)≤z≤0, then the lateral pressure at the calculation point is calculated using formula (3). The bottom of the seabed soil is used as the bottom of the calculation model, which can be determined based on the influence range of the foundation pit excavation. For foundation pits exceeding the influence range of the foundation pit excavation, the influence range is generally more than 3 times the depth of the foundation pit, based on experience. The passive side of the support structure is only in contact with the soil. Therefore, on the passive side of the support structure, if the calculation point is located between the bottom of the foundation pit and the bottom of the support structure, i.e., -(h1-b)≤z≤(h2-h1), then the lateral pressure at the calculation point is calculated using formula (4).

[0087] In step S13 above, the lateral pressure on the active side of the support structure is the pressure from the top of the pit to the bottom of the support structure on the outside of the pit, and the lateral pressure on the passive side of the support structure is the pressure from the bottom of the pit to the bottom of the support structure on the inside of the pit. Therefore, based on the lateral pressure σ at any point on the active side of the support structure under wave load calculated in step S2, t1 (z) and the lateral pressure σ at any point on the passive side of the support structure. t2 (z), the active lateral pressure E of the support structure under wave load can be obtained by integrating along the depth direction using formulas (1), (2) and (3). a，t The thickness h at the calculation point is generally taken as 1m and calculated in layers; and the passive lateral pressure E of the support structure under wave load can be obtained by integrating along the depth direction using formula (4). p，t The calculated lateral pressure E on the active side of the support structure. a，t and passive lateral pressure E of the support structurep，t The impact of changes in soil pore water pressure under water level fluctuations or wave loads on the foundation pit support structure is considered, which is of great significance for the safety control of foundation pits near rivers and coasts.

[0088] Furthermore, although the lateral pressure E of the support structure calculated by the method of considering pore pressure variation in this invention is obtained from the active side lateral pressure of the support structure... a，t and passive lateral pressure E of the support structure p，t The impact of soil pore water pressure changes under water level fluctuations or wave loads on the foundation pit support structure is considered. However, changes in soil pore water pressure under water level fluctuations or wave loads may not necessarily affect the foundation pit support structure. Therefore, to more accurately calculate the active and passive lateral pressures of the foundation pit support structure, the impact of soil pore water pressure changes under water level fluctuations or wave loads on the foundation pit support structure can be evaluated before the calculation. Based on this, the present invention also provides a method for evaluating the impact of pore pressure changes on the lateral pressure of the support structure, including the following steps:

[0089] S21. Using the above-mentioned method for calculating the lateral pressure of the support structure considering the pore pressure variation, calculate the active side lateral pressure and passive side lateral pressure of the support structure under wave load.

[0090] S22. Based on the lateral pressure on the active side of the support structure and the lateral pressure on the passive side of the support structure, calculate the first evaluation index characterizing the impact of wave load on the pressure of the support structure of the foundation pit, and calculate the ratio of the change amplitude of the difference between the lateral pressure on the active side of the support structure and the difference in earth pressure before the wave load, to obtain the first ratio. The first evaluation index includes relative active earth pressure and relative passive earth pressure. The relative active earth pressure is the ratio of the change amplitude of the lateral pressure on the active side of the support structure before and after the wave load to the lateral pressure on the active side of the support structure before the wave load. The relative passive earth pressure is the ratio of the change amplitude of the lateral pressure on the passive side of the support structure before and after the wave load to the lateral pressure on the passive side of the support structure before the wave load.

[0091] S23. Determine the boundary conditions of the theoretical model of the foundation pit;

[0092] S24. Based on boundary conditions, calculate a second evaluation index characterizing the influence of wave load on the change of excess pore pressure in soil. The second evaluation index includes a second ratio, which is the ratio of the change amplitude of total pore water pressure at the calculation point to the change amplitude of wave water pressure.

[0093] S25. Determine whether both the first evaluation index and the second evaluation index are less than a preset first threshold, and determine whether the first ratio is less than a preset second threshold.

[0094] S26. If yes, then the wave load has no effect on the pressure of the support structure; if no, then the wave load has an effect on the pressure of the foundation pit support structure.

[0095] In step S21 above, the specific calculation process is the same as in steps S11 to S13, and will not be repeated here.

[0096] In step S22 above, the step of calculating the first evaluation index characterizing the impact of wave load on the pressure of the support structure on the foundation pit, based on the active side lateral pressure and the passive side lateral pressure of the support structure, includes:

[0097] S221. Calculate the relative active earth pressure δE according to the following formula. a and relative passive earth pressure δE p :

[0098]

[0099]

[0100] In the formula, △E a E represents the amplitude of the change in lateral pressure on the active side of the support structure before and after wave loading. a，t，max E represents the maximum value of the active lateral pressure on the support structure after wave loading. a，t，min E represents the minimum lateral pressure on the active side of the support structure after wave loading. a，0 The active lateral pressure on the support structure before wave load is applied, ΔE p E represents the amplitude of the change in passive lateral pressure on the support structure before and after wave loading. p，t，max E represents the maximum passive lateral pressure on the support structure after wave loading. p，t，min The minimum passive lateral pressure on the support structure after wave loading, E p，0 The passive lateral pressure on the support structure before wave load.

[0101] In step S221 above, the relative active earth pressure δE a and relative passive earth pressure δE p All parameters are normalized. Since the lateral pressure on the active side and the passive side of the support structure changes continuously under wave load, the maximum value (wave peak) E of the lateral pressure on the active side of the support structure under wave load is taken. a，tmax and minimum value (trough) E a，t，min The lateral pressure E of the support structure without wave load is respectively compared with the active side pressure E. a，0 Subtract the two values ​​and take the larger absolute value of the difference as the amplitude ΔE of the change in lateral pressure on the active side of the support structure. a , where, according to Ea，t =∑σ t1 (z)*h, calculated based on the peak value, is E. a，t，max When calculated based on the trough, it is E. a，t，min The active lateral pressure E of the support structure without wave load. a，0 Calculations can be performed according to relevant standards; this is existing technology and will not be elaborated upon here. Similarly, the maximum value (wave crest) of the passive lateral pressure on the support structure under wave load is taken as E. p，t，max and minimum value (trough) E p，t，min The passive lateral pressure E of the support structure without wave load is respectively compared with that of the support structure without wave load. p，0 Subtract the two values ​​and take the larger absolute value of the difference as the amplitude of the change in lateral pressure on the passive side of the support structure, ΔE. p , where, according to E p，t =∑σ t2 (z)*h, calculated based on the peak value, is E. a，t，max When calculated based on the trough, it is E. a，t，min The passive lateral pressure E of the support structure without wave load. p，0 Calculations can be performed according to relevant standards; this is existing technology and will not be elaborated upon here.

[0102] In step S22 above, the first ratio is used to evaluate the degree of change in the total stress of the support structure caused by waves. Further, the steps of calculating the first ratio by dividing the change in the difference between the active side lateral pressure and the active side lateral pressure of the support structure by the difference in earth pressure before the wave load are included:

[0103] S222. The first ratio is calculated using the following formula:

[0104]

[0105] △E a-p =max{|(E a，t -E p，t ) max -(E a，t -E p，t )0|,|(E a，t -E p，t ) min -(E a，t -E p，t )0|}(18)

[0106] In the formula, △E a-p E represents the amplitude of the difference between the lateral pressure on the active side and the lateral pressure on the passive side of the support structure after wave loading. a，t -E p，t)0 represents the difference between the lateral pressure on the active side and the lateral pressure on the passive side of the support structure before wave load application. The subscript 0 indicates the value when there is no wave load application. (E) a，t -E p，t 0 = E a，0 -E p,0 E a，t E represents the active lateral pressure on the support structure after wave load application. p，t The passive lateral pressure on the support structure after wave load.

[0107] In step S222 above, since wave pressure has crests and troughs, it will cause the active side pressure of the foundation pit to increase or decrease. Here, the absolute value of the change is taken. Therefore, the difference between the pressure difference of the wave load at the crest (max) and the trough (min) is subtracted from the difference in soil pressure before the wave load is applied to represent the range of change of the difference.

[0108] In step S23 above, a theoretical analysis method is used to establish a theoretical model for foundation pit calculation, and then the boundary conditions of the theoretical model are determined. The boundary conditions include the total pore water pressure or excess pore water pressure of each boundary of the foundation pit. Each boundary includes the bottom boundary, left boundary, right boundary, bottom boundary of the foundation pit, water-stop curtain boundary, and seabed surface boundary.

[0109] Furthermore, in step S23, the step of determining the boundary conditions of the foundation pit theoretical model includes:

[0110] (1) Determine the bottom boundary conditions. When the seabed depth is finite and the bottom of the theoretical model is an impermeable boundary, the rate of change of pore water pressure along the depth direction at the boundary is 0, satisfying:

[0111]

[0112] In the formula, z is the depth below the seabed surface, i.e., the depth of the seabed soil, z = -h1, P t (z) represents the total pore water pressure at time t. The total pore water pressure is equal to the position water pressure plus the excess pore pressure, which is caused by waves or other effects.

[0113] (2) Determine the right boundary conditions. Since the foundation pit is symmetrical on both sides, take half of the foundation pit along the axis of symmetry in the middle of the pit for calculation and analysis. Then the right boundary is the axis of symmetry of the center of the foundation pit. Assuming it is an impermeable boundary, the derivative of the total pore water pressure along the depth direction at the boundary x = a1 + a2 is 0, which satisfies:

[0114]

[0115] In the formula, P t (z) represents the total pore water pressure and excess pore water pressure caused by wave action at time t;

[0116] (3) Determine the left boundary conditions. When -h1≤z≤0, the calculation point is in the seabed soil, satisfying formula (9). When 0≤z≤d, the calculation point is in the water, satisfying formula (10).

[0117]

[0118]

[0119] In the formula, P t (z) represents the total pore water pressure at time t, γ w Where is the specific weight of water, and H is the wave height. ω is the wave number, d is the still water level depth, k is the soil permeability coefficient, and z is the calculation depth, i.e. the bottom of the foundation pit, along the depth z direction;

[0120] (4) Determine the boundary conditions of the foundation pit bottom. Due to the need for excavation construction at the bottom of the foundation pit, the water head will be lowered to the excavation surface to ensure dry construction inside the foundation pit. Since this is a free surface, there is no excess pore water pressure. Assuming the water level is at the bottom of the foundation pit, x > a1, z = -(h1 - h2), indicating that the calculation point is at the bottom of the foundation pit, satisfying:

[0121] Pc t (z)=0 (11)

[0122] In the formula, Pc t (z) represents the excess pore water pressure at time t;

[0123] (5) Determine the boundary conditions of the water-stop curtain. Assume the water-stop curtain is impermeable, x = a1, z ≥ -(h1-b), indicating that the calculation point is inside the water-stop curtain. Since the inside of the water-stop curtain is impermeable, the following conditions are met:

[0124]

[0125] (6) Determine the seabed surface boundary conditions, where the groundwater level fluctuation is directly applied to the horizontal surface of the soil layer at z = d via pore pressure, satisfying:

[0126]

[0127] In the formula, P t (z) represents the excess pore water pressure at any point t on the seabed surface; z = d represents the calculation point on the seabed surface, simply indicating a point on the seabed surface;

[0128] The wave pressure applied to the surface of the seabed soil is:

[0129]

[0130] In the formula, p b This represents the maximum wave pressure acting on the surface of the seabed soil.

[0131] In step S24 above, the step of calculating the second evaluation index characterizing the influence of wave load on the change of soil excess pore pressure based on boundary conditions includes:

[0132] S241. If the calculation point is below the seabed, the second evaluation index shall be calculated using formula (15); if the calculation point is above the seabed, the second evaluation index shall be calculated using formula (16).

[0133]

[0134]

[0135] In the formula, P t，max (z) represents the maximum value of the total pore water pressure under the boundary conditions. γ is the average of all total pore water pressures under the boundary conditions. w It is the density of water.

[0136] In step S241 above, the second evaluation index is a normalized parameter used to evaluate the degree of change in soil excess pore pressure caused by waves.

[0137] In steps S25 and S26 above, the influence of pore water pressure on the support structure is evaluated based on the calculated first evaluation index, second evaluation index, and first ratio. Specifically, the relative active earth pressure δE is determined. a Relative passive earth pressure δE p The second ratio δp1, the second ratio δp2, and the first ratio δE a-p Does it satisfy the following formula (19)?

[0138]

[0139] If the conditions are met, the pore water pressure in the soil caused by wave loads has no effect on the support structure. In this case, existing standard methods can be used to calculate the active and passive lateral pressures of the support structure. If the conditions are not met, the pore water pressure in the soil caused by wave loads does affect the support structure. In this case, the active lateral pressure E of the support structure, calculated using the lateral pressure calculation method of this invention that considers pore pressure changes, can be used to calculate the lateral pressure E of the support structure. a，t and passive lateral pressure E of the support structure p，t This allows for the evaluation of the impact of pore water pressure in the soil caused by wave loads on the support structure. Different calculation methods can be used to calculate the active and passive lateral pressures on the support structure, enabling accurate calculation of the load on the foundation pit support structure under the action of soil pore water pressure changes. This is of great significance for the safety control of foundation pits near rivers and coasts.

[0140] Compared with existing technologies, the beneficial effects of this invention are as follows: It proposes a method for calculating and evaluating the degree of influence of the lateral pressure on the active side and the passive side of the support structure caused by changes in soil pore water pressure under water level fluctuations or wave loads. This solves the problem of the lack of methods for determining the value of external dynamic water load under river and coastal conditions in the current field of foundation pit support structure design, improves the design theory of foundation pit support structures, and is of great significance for the rational design and safety control of deep foundation pits.

[0141] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for calculating the lateral pressure of a support structure considering pore pressure variations, characterized in that, Includes the following steps: Establish a coordinate system with a point on the seabed surface as the origin, the direction towards the pit as the positive X-axis, and the vertical upward direction as the positive z-axis; Calculate the lateral pressure at any point on the active side of the support structure under wave load. Lateral pressure at any point on the passive side of the support structure The calculation formula is as follows: （1） （2） （3） （4） In the formula, The natural density of the seabed soil cover layer. The natural density of the seabed soil. The saturated unit weight of the seabed soil. For wave number, Let z be the wave angular frequency, and z be the depth below the seabed. denoted as , where is the distance between the top of the support structure and the seabed surface, and 'b' is the thickness from the bottom of the support structure to the bottom of the calculated seabed soil layer. The specific gravity of water; Based on formulas (1) to (3), integration along the depth direction yields the active lateral pressure of the support structure under wave load. Based on formula (4), the passive lateral pressure of the support structure under wave load is obtained by integrating along the depth direction. : （5） （6） In the formula, h is the thickness at the calculation point.

2. A method for evaluating the lateral pressure influence of a support structure considering pore pressure variations, characterized in that, Includes the following steps: Using the lateral pressure calculation method for the support structure considering pore pressure variation as described in claim 1, the active side lateral pressure and passive side lateral pressure of the support structure under wave load are calculated. Based on the lateral pressure on the active side of the support structure and the lateral pressure on the passive side of the support structure, a first evaluation index characterizing the impact of wave load on the pressure of the support structure of the foundation pit is calculated. The first ratio is obtained by calculating the ratio of the change amplitude of the difference between the active and passive lateral pressures of the support structure to the difference in earth pressure before the wave load. The first evaluation index includes relative active earth pressure and relative passive earth pressure. The relative active earth pressure is the ratio of the change amplitude of the active lateral pressure of the support structure before and after the wave load to the active lateral pressure of the support structure before the wave load. The relative passive earth pressure is the ratio of the change amplitude of the passive lateral pressure of the support structure before and after the wave load to the passive lateral pressure of the support structure before the wave load. Determine the boundary conditions of the theoretical model of the foundation pit; Based on boundary conditions, a second evaluation index characterizing the influence of wave load on the change of excess pore pressure in soil is calculated. The second evaluation index includes a second ratio, which is the ratio of the change amplitude of total pore water pressure at the calculation point to the change amplitude of wave water pressure. Determine whether both the first evaluation index and the second evaluation index are less than a preset first threshold, and determine whether the first ratio is less than a preset second threshold; If yes, then the wave load has no effect on the pressure of the support structure; if no, then the wave load has an effect on the pressure of the foundation pit support structure.

3. The method for evaluating the lateral pressure influence of support structures considering pore pressure variations according to claim 2, characterized in that, The steps for determining the boundary conditions of the foundation pit theoretical model include: (1) Determine the bottom boundary conditions. When the seabed depth is finite, the bottom of the theoretical model is an impermeable boundary, satisfying: （7） In the formula, z represents the depth below the seabed surface. The total pore water pressure at time t; (2) Determine the right-side boundary conditions. The right-side boundary is the central axis of symmetry of the foundation pit and is assumed to be an impermeable boundary, satisfying: （8） In the formula, Let t be the total pore water pressure caused by wave action at time t; (3) Determine the left boundary conditions. When the calculation point is in the seabed soil, it satisfies formula (9). When the calculation point is in the water, it satisfies formula (10). （9） （10） In the formula, The density of water, H is the wave height. For wave number, denoted as wave angular frequency, d as still water depth, k as soil permeability coefficient, and z as depth below the seabed surface. (4) Determine the boundary conditions at the bottom of the foundation pit. Assume the water level is at the bottom of the foundation pit and satisfies: （11） In the formula, Let be the excess pore water pressure at time t; (5) Determine the boundary conditions of the water-stop curtain. Assume that the water-stop curtain is impermeable and satisfies the following conditions: （12） (6) Determine the seabed surface boundary conditions, and apply the groundwater level fluctuation directly to the seabed using pore pressure. On the horizontal surface of the soil layer, the following conditions are met: （13） In the formula, Let t be the excess pore water pressure at any point on the seabed at time t; The wave pressure applied to the surface of the seabed soil is: （14） In the formula, This represents the maximum wave pressure acting on the surface of the seabed soil.

4. The method for evaluating the lateral pressure influence of support structures considering pore pressure variations according to claim 3, characterized in that, The steps for calculating the second evaluation index characterizing the influence of wave load on soil excess pore pressure based on boundary conditions include: If the calculation point is below the seabed, the second evaluation index is calculated using formula (15); if the calculation point is above the seabed, the second evaluation index is calculated using formula (16). （15） （16） In the formula, This represents the maximum total pore water pressure under the boundary conditions. This represents the average total pore water pressure under the boundary conditions. It is the density of water.

5. The method for evaluating the lateral pressure influence of support structures considering pore pressure variations according to claim 2, characterized in that, The steps for calculating the first evaluation index characterizing the impact of wave loads on the pressure of the support structure of the foundation pit, based on the active side lateral pressure and the passive side lateral pressure of the support structure, include: Calculate the relative active earth pressure using the following formula. and relative passive earth pressure : （15） （16） In the formula, This represents the amplitude of the change in lateral pressure on the support structure before and after wave loading. This represents the maximum value of the active lateral pressure on the support structure after wave loading. This represents the minimum lateral pressure on the active side of the support structure after wave loading. The active lateral pressure on the support structure before wave load is applied. This represents the amplitude of the change in passive lateral pressure on the support structure before and after wave loading. The maximum value of the passive lateral pressure on the support structure after wave loading. Minimum passive lateral pressure on the support structure after wave loading. The passive lateral pressure on the support structure before wave load.

6. The method for evaluating the lateral pressure influence of support structures considering pore pressure variations according to claim 2, characterized in that, The step of calculating the ratio of the change amplitude of the difference between the active side lateral pressure and the passive side lateral pressure of the support structure to the difference in earth pressure before the wave load, to obtain the first ratio, includes: The first ratio is calculated using the following formula: （17） （18） In the formula, This represents the magnitude of the difference between the lateral pressure on the active side and the lateral pressure on the passive side of the support structure after wave loading. This represents the difference between the lateral pressure on the active side and the lateral pressure on the passive side of the support structure before wave loading. The active lateral pressure on the support structure after wave load is applied. The passive lateral pressure on the support structure after wave load.

7. The method for evaluating the lateral pressure influence of support structures considering pore pressure variations according to claim 2, characterized in that, The preset first threshold is 10%, and the preset second threshold is 5%.

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