Foundation anti-seismic liquefaction evaluation method based on long and large underground structure

Abstract

The invention provides a foundation anti-seismic liquefaction evaluation method based on a long and large underground structure, and belongs to the technical field of geotechnical engineering and pile foundations, and the method comprises the following steps: S1, constructing a three-dimensional free field finite element model; s2, calculating response parameters of the soil layer under the earthquake action; s3, extracting displacement time history data of the cross section of the underground structure by using the response parameters of the soil layer under the earthquake action; s4, constructing a shell-spring model of the long and large underground structure; s5, taking the extracted displacement time history data as boundary conditions of the shell-spring model; s6, solving a dynamic balance equation of the shell-spring model, and calculating dynamic response parameters of the long and large underground structure under the earthquake action; s7, the liquefaction degree of the foundation of the long and large underground structure is evaluated; and S8, corresponding anti-seismic reinforcement measures are put forward. According to the foundation anti-seismic liquefaction evaluation method based on the long and large underground structure, accurate evaluation of the foundation liquefaction phenomenon can be achieved, and anti-seismic design and construction of the long and large underground structure are guided.

Description

Technical Field

[0001] The invention relates to the field of geotechnical engineering and pile foundation technology, and in particular to a foundation seismic liquefaction assessment method based on a long and large underground structure. Background Art

[0002] Earthquakes are sudden and destructive natural disasters with wide and far-reaching impacts. Earthquakes not only cause a large number of casualties, but also cause huge property losses. Especially in urban areas, with the widespread application of long underground structures, the seismic performance assessment of long underground structures such as subways and underground integrated pipelines is particularly important.

[0003] In the prior art, most of the research focuses on the seismic performance of above-ground structures, but relatively few studies have been conducted on the impact of earthquakes on underground structures. Under the action of earthquakes, the foundation of underground structures is very susceptible to liquefaction, that is, the foundation soil loses its original strength and stability under the action of seismic waves and forms a liquid-like state, which leads to a sharp drop in the bearing capacity of the foundation and further causes the destruction of underground structures. The liquefaction of foundation soil is not only affected by inherent factors such as geological age and clay content, but also by external conditions such as groundwater level, earthquake magnitude and duration.

[0004] For long underground structures, the foundation conditions are more complex, and the propagation law of seismic waves is significantly different from that of traditional ground structures. In addition, existing assessment methods often have problems such as complex calculations and insufficient accuracy. In addition, existing studies mostly consider soil conditions, drainage conditions, static conditions, and dynamic conditions, which is not comprehensive. Therefore, seismic liquefaction assessment of the foundation of long underground structures is an important measure to ensure the safety of underground structures. Summary of the invention

[0005] The purpose of the present invention is to provide a foundation seismic liquefaction assessment method based on a long and large underground structure. By combining the three-dimensional free-field nonlinear seismic effect analysis with the longitudinal shell-spring model seismic analysis of the underground structure, the sand liquefaction constitutive method is used to assign values ​​to the soil layer material parameters, so as to achieve an accurate assessment of the foundation liquefaction phenomenon and guide the seismic design and construction of the long and large underground structure.

[0006] To achieve the above object, the present invention provides a method for evaluating the seismic liquefaction of a foundation based on a long underground structure, comprising the following steps:

[0007] S1. Construct a three-dimensional free-field finite element model;

[0008] S2. Apply the seismic wave time history curve as the boundary condition at the bottom boundary of the three-dimensional free-field finite element model to calculate the response parameters of the soil layer under the earthquake action;

[0009] S3, extracting displacement time history data of the cross section of the underground structure using the response parameters of the soil layer under the earthquake action calculated in step S2;

[0010] S4. According to the geometric dimensions and material properties of the long underground structure, a shell-spring model of the long underground structure is constructed, wherein the shell unit simulates the main part of the long underground structure, and the spring unit simulates the interaction between the soil layer and the long underground structure;

[0011] S5, using the displacement time history data extracted in step S3 as the boundary condition of the shell-spring model;

[0012] S6. Solve the dynamic equilibrium equation of the shell-spring model and calculate the dynamic response parameters of the long underground structure under earthquake action;

[0013] S7. According to the dynamic response parameters of the long underground structure and the preset liquefaction evaluation index, the liquefaction degree of the foundation of the long underground structure is evaluated, and the seismic performance of the foundation of the long underground structure is analyzed;

[0014] S8. According to the analysis results of step S7, corresponding earthquake-resistant reinforcement measures are proposed.

[0015] Preferably, in step S1, constructing a three-dimensional free-field finite element model includes the following sub-steps:

[0016] S11. Establish a database of foundation liquefaction assessment indicators and liquefaction influencing factors for long and large underground structures;

[0017] S12. Using finite element software, according to the database established in step S11, construct a three-dimensional free-field finite element model of a large underground structure, and then perform meshing (the meshing should take into account the balance between calculation accuracy and calculation efficiency. For soil layer areas where liquefaction may occur, the mesh should be appropriately encrypted to improve calculation accuracy), and then perform soil layer material assignment (according to the physical and mechanical properties of the soil, assign corresponding material parameters to the soil layer materials in the model, such as density, elastic modulus, Poisson's ratio, etc. For soil layers that may liquefy, special consideration should be given to their liquefaction characteristics, such as liquefaction potential, liquefaction strength, etc.).

[0018] S13. Apply boundary conditions to the constructed three-dimensional free-field finite element model.

[0019] Preferably, in step S11, the liquefaction evaluation index is a liquefaction index, and the calculation formula is as follows:

[0020]

[0021] Among them, I LE is the liquefaction index; d i is the soil layer thickness; ω iis the weight factor; N is the number of soil layers; i is the starting value of the soil layer.

[0022] Preferably, in step S11, the liquefaction influencing factors include geological survey data, historical earthquake data, meteorological data, large and large underground structure data and external loads; wherein the geological survey data include geological structure, soil layer distribution, groundwater level and soil physical properties; the historical earthquake data include earthquake acceleration, magnitude, waveform, direction and frequency; the meteorological data is precipitation; the large and large underground structure data include the geometric dimensions, material properties and burial depth of the underground structure; the external loads include building loads and vibration loads (long-term traffic vibration and mechanical vibration) located above the large and large underground structure.

[0023] Preferably, in step S12, in the three-dimensional free-field finite element model, a sand liquefaction constitutive model is used to assign values ​​to the soil layer material. The sand liquefaction constitutive model is based on the nested yield surface hardening rule and introduces an optimized equivalent shear strain algorithm to ensure the accuracy of simulating the soil layer liquefaction process.

[0024] Preferably, the yield surface equation of the sand liquefaction constitutive model is as follows:

[0025] f=32[s-(p+p 0 )α]:[s-(p+p 0 )α]-M 2 (p+p 0 ) 2

[0026] Where f is the yield state; s is the deviatoric stress tensor; p is the effective mean normal stress; p 0 is the residual strength corresponding to the initial liquefaction of saturated sand; α is the coordinate of the center point of the yield surface on the deviatoric stress plane; in is the internal friction angle of saturated sand.

[0027] Preferably, the calculation formula of the optimized equivalent shear strain algorithm is as follows:

[0028]

[0029] Among them, γ eq is the equivalent shear strain; ij is the strain tensor; M ij is the weight factor.

[0030] Preferably, in step S13, a fixed constraint is applied to the bottom of the three-dimensional free-field finite element model, and a rolling constraint is applied to the side of the three-dimensional free-field finite element model.

[0031] Preferably, in step S3, the displacement time history data includes: time information, displacement value, displacement direction and node number.

[0032] Time information: record the time point or time step corresponding to each displacement data point.

[0033] Displacement value: includes the displacement components of each node or unit on the cross section in the three directions of X, Y, and Z (or directions determined according to actual conditions). The displacement components reflect the deformation of the structure in different directions.

[0034] Displacement direction: Since displacement is a vector, each displacement value contains two pieces of information: magnitude and direction.

[0035] Node or element number: To distinguish the displacement data at different locations on the cross section, a unique number is assigned to each node or element. In the displacement time history data, these numbers are used to identify the displacement values ​​at different locations.

[0036] Preferably, the dynamic equilibrium equation of the shell-spring model is:

[0037] MU+CU+KU=F(t)

[0038] Among them, M, C, K are mass matrix, damping matrix and stiffness matrix respectively; U is the displacement vector; F(t) is the external excitation, that is, the seismic wave.

[0039] Therefore, the present invention adopts the above-mentioned foundation seismic liquefaction assessment method based on a long underground structure, and the beneficial technical effects are as follows:

[0040] (1) The present invention uses a method combining three-dimensional free-field nonlinear seismic effect analysis with longitudinal shell-spring model seismic analysis of long and large underground structures, which can accurately simulate the liquefaction phenomenon of underground structure foundations under earthquake action;

[0041] (2) The present invention improves the calculation efficiency and reduces the calculation cost by optimizing the sandy soil constitutive model and calculation process;

[0042] (3) The present invention discloses that the factors that affect the liquefaction of the foundation of a large underground structure include geological survey data, historical earthquake data, meteorological data, large underground structure data and external loads, which are more comprehensive than those considered in traditional research and are conducive to improving the accuracy of the evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A flow chart of a method for evaluating the seismic liquefaction of a foundation based on a long underground structure according to the present invention;

[0044] Figure 2 The present invention provides a foundation liquefaction influencing factor diagram for a foundation seismic liquefaction assessment method based on a long underground structure. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical scheme and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention are further described in detail in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not intended to limit the embodiments of the present invention. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions.

[0046] It should be noted that the terms "include", "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or server comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or devices.

[0047] Like reference numerals and letters denote similar items in the following drawings, and thus, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0048] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, or are directions or positional relationships in which the product of the invention is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0049] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "setting", "installation" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0050] Embodiment 1

[0051] like Figure 1 FIG. 1 is a flow chart of a method for evaluating the seismic liquefaction of a foundation based on a long underground structure according to the present invention, comprising the following steps:

[0052] S1. Constructing a three-dimensional free-field finite element model, including the following sub-steps:

[0053] S11. Establish a database of foundation liquefaction assessment indicators and liquefaction influencing factors for long and large underground structures;

[0054] The liquefaction assessment indicator is the liquefaction index.

[0055] The liquefaction index calculation formula is as follows:

[0056]

[0057] Among them, I LE is the liquefaction index; d i is the soil layer thickness; ω i is the weight factor; N is the number of soil layers; i is the starting value of the soil layer.

[0058] like Figure 2 As shown, this embodiment takes into account the factors affecting the liquefaction of the foundation of a large underground structure, geological survey data, historical earthquake data, meteorological data, large underground structure data and external loads, and the factors considered are complete;

[0059] Among them, geological survey data include geological structure, soil layer distribution, groundwater level and soil physical properties; historical earthquake data include earthquake acceleration, magnitude, waveform, direction and frequency; meteorological data are precipitation; long and large underground structure data include the geometric dimensions, material properties and burial depth of the underground structure; external loads include building loads and vibration loads located above the long and large underground structure (long-term traffic vibration and mechanical vibration will affect the degree of liquefaction of the foundation of the underground structure).

[0060] S12, using finite element software according to the database established in step S11, constructing a three-dimensional free-field finite element model of a long underground structure; wherein, firstly, defining the nodes and required units on the axis of the long underground structure model (such as a tunnel and a pipe gallery); then defining material properties and interface properties, including parameters such as elastic modulus, Poisson's ratio, and density of the soil; finally, using finite element software (such as ABAQUS) to establish a refined three-dimensional free-field finite element model to simulate the propagation and interaction of seismic waves in the soil layer;

[0061] Then, meshing is performed (the meshing should consider the balance between calculation accuracy and calculation efficiency. For the soil layer area where liquefaction may occur, the mesh should be appropriately encrypted to improve the calculation accuracy), and then the soil layer material is assigned (according to the physical and mechanical properties of the soil, the soil layer materials in the model are assigned corresponding material parameters, such as density, elastic modulus, Poisson's ratio, etc. For the soil layer that may liquefy, its liquefaction characteristics, such as liquefaction potential, liquefaction strength, etc., are specially considered);

[0062] In the three-dimensional free-field finite element model, the sand liquefaction constitutive model is used to assign values ​​to the soil layer materials. The sand liquefaction constitutive model is based on the nested yield surface hardening rule, and an optimized equivalent shear strain algorithm is introduced to ensure the accuracy of simulating the soil liquefaction process.

[0063] The yield surface equation of the sand liquefaction constitutive model is as follows:

[0064] f=32[s-(p+p 0 )α]:[s-(p+p 0 )α]-M 2 (p+p 0 ) 2

[0065] Where f is the yield state; s is the deviatoric stress tensor; p is the effective mean normal stress; p 0 is the residual strength corresponding to the initial liquefaction of saturated sand; α is the coordinate of the center point of the yield surface on the deviatoric stress plane; in is the internal friction angle of saturated sand.

[0066] The calculation formula of the optimized equivalent shear strain algorithm is as follows:

[0067]

[0068] Among them, γ eq is the equivalent shear strain; ij is the strain tensor; M ij is the weight factor. Using the optimized equivalent shear strain algorithm to replace the original shear strain algorithm can improve the calculation accuracy and efficiency of the model.

[0069] S13. Apply boundary conditions to the constructed three-dimensional free-field finite element model.

[0070] Specifically, a fixed constraint is applied to the bottom of the three-dimensional free-field finite element model, and a rolling constraint is applied to the side of the three-dimensional free-field finite element model.

[0071] S2. Apply the seismic wave time history curve as the boundary condition at the bottom boundary of the three-dimensional free-field finite element model to calculate the response parameters of the soil layer under the earthquake action;

[0072] S3, extracting displacement time history data of the cross section of the underground structure using the response parameters of the soil layer under the earthquake action calculated in step S2;

[0073] The displacement time history data includes: time information, displacement value, displacement direction and node number.

[0074] Time information: record the time point or time step corresponding to each displacement data point.

[0075] Displacement value: includes the displacement components of each node or unit on the cross section in the X, Y, and Z directions (or directions determined according to actual conditions).

[0076] Displacement direction: Since displacement is a vector, each displacement value contains two pieces of information: magnitude and direction.

[0077] Node or element number: To distinguish the displacement data at different locations on the cross section, a unique number is assigned to each node or element. In the displacement time history data, these numbers are used to identify the displacement values ​​at different locations.

[0078] S4. According to the geometric dimensions and material properties of the long underground structure, a shell-spring model of the long underground structure is constructed, wherein the shell unit simulates the main part of the long underground structure, and the spring unit simulates the interaction between the soil layer and the long underground structure;

[0079] The dynamic equilibrium equation of the shell-spring model is:

[0080] MU+CU+KU=F(t)

[0081] Among them, M, C, K are mass matrix, damping matrix and stiffness matrix respectively; U is the displacement vector; F(t) is the external excitation, that is, the seismic wave.

[0082] S5, using the displacement time history data extracted in step S3 as the boundary condition of the shell-spring model;

[0083] S6. Solve the dynamic equilibrium equation of the shell-spring model and calculate the dynamic response parameters of the long underground structure under earthquake action;

[0084] S7. According to the dynamic response parameters of the long underground structure and the preset liquefaction evaluation index, the liquefaction degree of the foundation of the long underground structure is evaluated, and the seismic performance of the foundation of the long underground structure is analyzed;

[0085] Dynamic response calculation:

[0086] Run the shell-spring model to calculate the dynamic response parameters (such as displacement, stress, acceleration, etc.) of the underground structure under earthquake action.

[0087] Analyze the deformation of underground structures to determine whether they are unstable or damaged.

[0088] Liquefaction degree assessment:

[0089] The liquefaction degree of foundation soil is evaluated based on the soil layer response calculation results.

[0090] Indicators such as liquefaction index and liquefaction potential are used for quantitative assessment to determine the impact of liquefaction on underground structures.

[0091] Performance analysis and optimization:

[0092] Based on the evaluation results, the seismic performance of the underground structure is analyzed.

[0093] Propose corresponding seismic reinforcement measures or design optimization suggestions to improve the seismic resistance of underground structures.

[0094] S8. According to the analysis results of step S7, corresponding earthquake-resistant reinforcement measures are proposed.

[0095] The evaluation process, results, suggestions and other contents are compiled into an evaluation report. Afterwards, the evaluation report is submitted to the relevant units or departments for reference and decision-making.

[0096] The present invention also provides a foundation seismic liquefaction assessment system for a long underground structure, comprising a three-dimensional free-field finite element model construction module, a sand liquefaction constitutive model assignment module, a seismic effect analysis module, a shell-spring model construction module, a dynamic response calculation module, a liquefaction assessment and performance analysis module, and a report generation module;

[0097] Among them, the three-dimensional free-field finite element model construction module is used to construct a three-dimensional free-field finite element model;

[0098] The sand liquefaction constitutive model assignment module is used to assign values ​​to soil materials using the sand liquefaction constitutive model in a three-dimensional free field model;

[0099] Seismic effect analysis module, used to calculate the response parameters of soil layers under earthquake action and extract displacement time history data;

[0100] Shell-spring model building module, used to build shell-spring models of underground structures;

[0101] Dynamic response calculation module, used to solve the overall dynamic equilibrium equation of the shell-spring model and calculate the dynamic response parameters of the underground structure;

[0102] Liquefaction Assessment and Performance Analysis module, used to assess the liquefaction degree of foundation soil and analyze the seismic performance of underground structures;

[0103] The report generation module is used to generate evaluation reports.

[0104] It is worth noting that the contents not elaborated in detail in the present invention are all prior art and are well known to those skilled in the art.

[0105] Therefore, the present invention adopts the above-mentioned foundation seismic liquefaction assessment method based on long and large underground structures. By combining the three-dimensional free-field nonlinear seismic effect analysis with the longitudinal shell-spring model seismic analysis of the underground structure, the sand liquefaction constitutive method is used to assign values ​​to the soil layer material parameters, thereby achieving an accurate assessment of the foundation liquefaction phenomenon and guiding the seismic design and construction of long and large underground structures.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for evaluating the seismic liquefaction of a long underground structure, characterized in that: The following steps are involved: S1. Construct a three-dimensional free-field finite element model; S2. Apply the seismic wave time history curve as the boundary condition at the bottom boundary of the three-dimensional free-field finite element model to calculate the response parameters of the soil layer under the earthquake action; S3, extracting displacement time history data of the cross section of the underground structure using the response parameters of the soil layer under the earthquake action calculated in step S2; S4. According to the geometric dimensions and material properties of the long underground structure, a shell-spring model of the long underground structure is constructed, wherein the shell unit simulates the main part of the long underground structure, and the spring unit simulates the interaction between the soil layer and the long underground structure; S5, using the displacement time history data extracted in step S3 as the boundary condition of the shell-spring model; S6. Solve the dynamic equilibrium equation of the shell-spring model and calculate the dynamic response parameters of the long underground structure under earthquake action; S7. According to the dynamic response parameters of the long underground structure and the preset liquefaction evaluation index, the liquefaction degree of the foundation of the long underground structure is evaluated, and the seismic performance of the foundation of the long underground structure is analyzed; S8. According to the analysis results of step S7, corresponding earthquake-resistant reinforcement measures are proposed.

2. The method for evaluating seismic liquefaction of a long underground structure according to claim 1, characterized in that: In step S1, a three-dimensional free-field finite element model is constructed, including the following sub-steps: S11. Establish a database of foundation liquefaction assessment indicators and liquefaction influencing factors for long and large underground structures; S12, using finite element software according to the database established in step S11, constructing a three-dimensional free-field finite element model of the long underground structure, then performing meshing, and then assigning soil layer materials; S13. Apply boundary conditions to the constructed three-dimensional free-field finite element model.

3. The method for evaluating the seismic liquefaction of a long underground structure according to claim 2, characterized in that: In step S11, the liquefaction evaluation index is the liquefaction index, and the calculation formula is as follows: Among them, I LE is the liquefaction index; d i is the soil layer thickness; ω i is the weight factor; N is the number of soil layers; i is the starting value of the soil layer.

4. The method for evaluating seismic liquefaction of a long underground structure according to claim 3, characterized in that: In step S11, the liquefaction influencing factors include geological survey data, historical earthquake data, meteorological data, large and large underground structure data and external loads; wherein, the geological survey data include geological structure, soil layer distribution, groundwater level and soil physical properties; the historical earthquake data include earthquake acceleration, magnitude, waveform, direction and frequency; the meteorological data is precipitation; the large and large underground structure data include the geometric dimensions, material properties and burial depth of the underground structure; the external load includes the building load and vibration load located above the large and large underground structure.

5. The method for evaluating the seismic liquefaction of a long underground structure according to claim 4, characterized in that: In step S12, in the three-dimensional free-field finite element model, the sand liquefaction constitutive model is used to assign values ​​to the soil layer material. The sand liquefaction constitutive model is based on the nested yield surface hardening rule and introduces an optimized equivalent shear strain algorithm to ensure the accuracy of simulating the soil liquefaction process.

6. The method for evaluating the seismic liquefaction of a long underground structure according to claim 5, characterized in that: The yield surface equation of the sand liquefaction constitutive model is as follows: f=32[s-(p+p0)α]:[s-(p+p0)α]-M 2 (p+p0) 2 Where f is the yield state; s is the deviatoric stress tensor; p is the effective average normal stress; p0 is the residual strength corresponding to the initial liquefaction of saturated sand; α is the coordinate of the center point of the yield surface on the deviatoric stress plane; in is the internal friction angle of saturated sand.

7. The method for evaluating the seismic liquefaction of a long underground structure according to claim 6, characterized in that: The calculation formula of the optimized equivalent shear strain algorithm is as follows: Among them, γ eq is the equivalent shear strain; ij is the strain tensor; M ij is the weight factor.

8. The method for evaluating the seismic liquefaction of a long underground structure according to claim 7, characterized in that: In step S13, a fixed constraint is applied to the bottom of the three-dimensional free-field finite element model, and a rolling constraint is applied to the side of the three-dimensional free-field finite element model.

9. The method for evaluating seismic liquefaction of a long underground structure according to claim 8, characterized in that: In step S3, the displacement time history data includes: time information, displacement value, displacement direction and node number.

10. A method for evaluating seismic liquefaction of a long underground structure according to claim 9, characterized in that: The dynamic equilibrium equation of the shell-spring model is: MU+CU+KU=F(t) Among them, M, C, K are mass matrix, damping matrix and stiffness matrix respectively; U is the displacement vector; F(t) is the external excitation, that is, the seismic wave.

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