Earth and rockfill dam foundation seismic liquefaction partition discrimination method

Abstract

The invention discloses an earth and rockfill dam foundation seismic liquefaction partition discrimination method. The method comprises the following steps: performing an indoor test on a target dam foundation soil body to obtain basic physical performance parameters; according to the basic physical performance parameters, modeling considering anti-seepage measures is conducted on the dam foundation of the target dam body, and dam foundation stress field distribution is obtained through static finite element analysis; the dam foundation is subjected to corresponding preliminary static parameter partitioning; carrying out a soil body dynamic strength test according to a numerical simulation result so as to obtain the anti-liquefaction strength of the test soil body; dynamic analysis is conducted, the dynamic load and earthquake acceleration response distribution rule borne by soil bodies of all parts of the dam foundation is obtained, and then dynamic parameter re-partitioning is conducted on the dam foundation; and the seismic liquefaction safety is correspondingly and jointly analyzed by static and dynamic parameter partitions. According to the method, the influence of anti-seepage measures and various working conditions on the dam foundation stress field is considered, full-section and whole-process evaluation of dam foundation liquefaction safety is improved, the anti-liquefaction measures are more targeted and regional, and concise suggestions can be provided for engineering construction.

Description

Technical Field

[0001] The present invention belongs to the technical field of seismic resistance of geotechnical structures in geotechnical earthquake engineering, and specifically relates to a method for discriminating seismic liquefaction zoning of the dam foundation of an earth-rock dam. Background Technique

[0002] The proposed water conservancy structures (constructions) usually have huge geometric dimensions, and their overall spatial distribution has a certain depth (generally up to 2 km along the river direction). The mechanical conditions of the soil on both sides of the upstream and downstream of the dam body will show differences, the seismic responses will be different, and the anti-liquefaction strengths under seismic action will also be different. There is a possibility of seismic liquefaction, and seismic liquefaction discrimination is required. After building the dam, the stress field and seepage field of the dam foundation will change further, and the seismic liquefaction discrimination of the dam foundation needs to be improved accordingly for this change.

[0003] Existing codes and engineering methods often make judgments based on in-situ test data of natural sites, and the depth range is generally about 20 m. There is also little involvement in safety evaluation during the service period, and it cannot fully meet the liquefaction safety assessment of earth-rock dam foundations with similar huge geometric dimensions and depth. There is an urgent need to develop a new method that can consider the analysis of the anti-liquefaction performance of the dam foundation. Liquefaction of saturated soil refers to the fact that under dynamic loads such as earthquakes, the soil skeleton has a tendency to shear and contract, which in turn leads to an increase in the excess pore water pressure of the saturated soil and a decrease in the effective stress, causing the soil to partially or completely lose its shear strength and become like "liquid". Finite Element Method (FEM) calculation and analysis is one of the important scientific means for dealing with complex engineering problems at present. FEM transforms the problem of continuous physical and mechanical differential or partial differential equations into a discrete problem that is convenient for computer calculation and solution through numerical approximation methods, so as to realize the solution of differential or partial differential equations. Through the simulation of geotechnical related projects such as earth-rock dam projects by the finite element method, the stress state or deformation of the earth-rock dam under various working conditions can be obtained relatively accurately and conveniently. The unit test of soil in geotechnical engineering is used to study the characteristics of the soil unit at the scale level. The unit test represented by the indoor dynamic triaxial test mainly aims at the evaluation of the anti-liquefaction ability of saturated sand, and the dynamic strength curve of the sand can be obtained, so as to provide a basis for liquefaction discrimination. The existing technology lacks a means to combine finite element calculation and analysis to identify the differences in the initial mechanical state and seismic response of the upstream and downstream of the earth-rock dam and the dam foundation under the dam body, and lacks a unit test method for these differences, so as to make a reliable seismic liquefaction discrimination of the dam foundation. Summary of the Invention

[0004] In order to solve the problems in the background technique, the purpose of the present invention is to provide a method for discriminating seismic liquefaction zoning of the dam foundation of an earth-rock dam.

[0005] The technical solution adopted by the present invention is as follows, including the following steps:

[0006] Step S1. First, conduct indoor tests on the soil of the target earth-rock dam foundation, and at the same time, combine relevant geological exploration reports to obtain the basic physical property parameters of the foundation soil; the basic physical property parameters of the foundation soil include the specific gravity, maximum void ratio, minimum void ratio, permeability coefficient, and internal friction angle of the foundation soil;

[0007] Step S2. Based on the basic physical property parameters of the foundation soil, model the entire target earth-rock dam to obtain a finite element model of the target earth-rock dam. Then, conduct a static finite element analysis on the finite element model to obtain the stress field distribution of the earth-rock dam foundation under different working conditions;

[0008] Step S3. According to the stress field distribution of the earth-rock dam foundation, conduct a preliminary static partition of the earth-rock dam foundation;

[0009] Step S4. Then, conduct soil element tests on the soil of the earth-rock dam foundation to obtain the overburden stress influence coefficient and static shear stress influence coefficient of the soil element under different effective overburden stresses and static shear stress ratios;

[0010] Step S5. Next, update the parameters of the finite element model of the earth-rock dam according to the overburden stress influence coefficient and static shear stress influence coefficient in Step S4, conduct a dynamic analysis on the finite element model with updated parameters, and re-partition the earth-rock dam foundation according to the dynamic analysis results;

[0011] Step S6. Conduct liquefaction discrimination on the earth-rock dam foundation according to the partition result obtained in Step S5 to obtain the liquefaction discrimination result of the target earth-rock dam foundation.

[0012] In the above Step S2, the modeling process of the finite element model corresponding to the target earth-rock dam is as follows:

[0013] Step S2.1. First, construct a finite element model in proportion according to the actual size of the on-site site, and simultaneously model the anti-seepage measures in the on-site site. At the same time, set the parameters of the finite element model with the basic physical property parameters of the foundation soil obtained in Step S1;

[0014] The anti-seepage measures include concrete cut-off walls, composite geomembranes, etc.

[0015] Step S22. Use different water levels to simulate the load conditions of the target earth-rock dam under different working conditions. The working conditions of the target earth-rock dam include the construction period and the service period, and the service period includes the normal water storage period and the flood period. By changing the water level corresponding to the finite element model, obtain the stress field distribution of the finite element model of the target earth-rock dam during the construction period and the service period.

[0016] The specific content of the above Step S3 is:

[0017] Step S31: First, according to the stress field distribution of the earth-rock dam foundation, obtain the static shear stress ratio α of each soil element in the foundation:

[0018]

[0019] where τ s is the static shear stress of the soil element; σ is the overlying effective stress of the soil element;

[0020] Step S32: Next, conduct a preliminary static force zoning for the earth-rock dam foundation. The earth-rock dam foundation is divided into three regions: the upstream water storage area U, the central weight area C, and the downstream seepage area D. The upstream water storage area and the downstream seepage area are located on both sides of the central weight area respectively, and the upstream water storage area and the downstream seepage area are located in the upstream and downstream regions of the earth-rock dam respectively. The zoning method of the earth-rock dam foundation is determined as follows:

[0021] Compare the static shear stress ratio of each soil element in the foundation with a preset static shear stress ratio threshold:

[0022] If the static shear stress ratio of the soil element under all working conditions is less than the static shear stress ratio threshold, it indicates that the soil element is less affected by the static shear stress, and the soil element is classified into the central weight area;

[0023] Otherwise, it indicates that the soil element is more affected by the static shear stress, and the soil element is classified into the upstream water storage area or the downstream seepage area according to the water level line where the soil element is located.

[0024] In step S3, for a horizontal site with an earth-rock dam, different from a shallow free horizontal site, due to the influence of initial static shear stress and overlying stress, there are soil elements with different initial stress states in different regions under the dam foundation, and its initial stress state is complex. At the same time, due to the actual situations such as water storage in the dam reservoir area and the design of cut-off walls, a stable seepage field will be formed inside the dam foundation soil, which further changes the initial stress state of the dam foundation soil area. The initial stress state is specifically characterized by the overlying effective stress and the initial static shear stress, and the distinction of the regional initial stress state is based on different combinations of the overlying effective stress and the initial static shear stress ratio.

[0025] The zoning basis is the difference in the combination and change of the overlying effective stress and the initial shear stress in the region. It is mainly reflected in that due to the influence of dam construction, the dam foundation, which was originally a horizontal site, has initial static shear stress in the regions on both sides of the dam body, while the dam foundation region directly under the dam body has a larger overlying effective stress than that on both sides. The influence of the seepage field during service makes the change of the initial static shear stress upstream and downstream also show differences, so the above zoning is made.

[0026] The specific content of the described step S4 is as follows:

[0027] Step S41: First, conduct soil element tests on the soil of the earth-rock dam foundation under different overlying effective stresses σ, obtain the liquefaction resistance strength of the soil element under different overlying effective stresses and static shear stress ratios, and obtain the overlying stress influence coefficient K of the soil element under different overlying effective stresses σ according to the following formula σ :

[0028]

[0029] In the formula, K σ represents the overlying stress influence coefficient under the overlying effective stress σ; CRR σ，α＝0 represents the liquefaction resistance strength of the soil under the overlying effective stress σ when the static shear stress ratio α obtained from the soil element test is 0; CRR σ＝100kPa，α＝0 represents the liquefaction resistance strength of the soil when the static shear stress ratio α obtained from the soil element test is 0 and the overlying effective stress σ is 100 kPa;

[0030] Step S42: Then, conduct soil element tests on the soil of the earth-rock dam foundation under different static shear stress ratios α, and obtain the static shear stress influence coefficient K of the soil element under different static shear stress ratios α by processing according to the following formula α :

[0031]

[0032] In the formula, K α represents the static shear stress influence coefficient under the static shear stress ratio α; CRR σ,α represents the liquefaction resistance strength of the soil under the static shear stress ratio α and the overlying effective stress σ obtained from the soil element test.

[0033] The specific content of the above-mentioned step S5 is as follows:

[0034] Step S51: First, set the parameters of the finite element model of the earth-rock dam according to the overlying stress influence coefficient and static shear stress influence coefficient obtained in step S4;

[0035] The overlying stress influence coefficient K σ is used to set the parameters of the central weight area C of the preliminary static force partition, and the static shear stress influence coefficient K α is used to set the parameters of the upstream water storage area U and the downstream seepage area D of the preliminary static force partition;

[0036] Step S52: Then, input the seismic wave for seismic liquefaction dynamic analysis into the finite element model after updating the parameters. The seismic wave adopts an equal-amplitude sine wave, and the maximum acceleration amplitude of the seismic wave adopts the actual maximum acceleration amplitude of the on-site site;

[0037] Step S53: Next, perform seismic liquefaction dynamic analysis on the finite element model of the input seismic wave to obtain the overlying effective stress σ' of the finite element model under the action of the seismic wave v and the dynamic shear stress τ av , and process according to the following formula to obtain the dynamic shear stress ratio CSR of each soil element in the dam foundation:

[0038]

[0039] where τ av is the dynamic shear stress of the soil element; σ' v is the overlying effective stress of the soil element;

[0040] Step S54: Then, re - perform dynamic zoning on the dam foundation of the rock - fill dam according to the dynamic shear stress ratio CSR of the soil element. The dynamic zoning method of the dam foundation of the rock - fill dam is determined as follows:

[0041] Compare the dynamic shear stress ratio of each soil element in the dam foundation with a preset dynamic shear stress ratio threshold:

[0042] If the dynamic shear stress ratio of the soil element under all working conditions is less than the dynamic shear stress ratio threshold, it indicates that the soil element is less affected by the dynamic shear stress, and this soil element is classified into the central weight - loading area;

[0043] Otherwise, it indicates that the soil element is more affected by the dynamic shear stress, and this soil element is classified into the upstream water - storage area or the downstream seepage area according to the water level line where the soil element is located.

[0044] Adjust the static zoning result according to the finite - element simulation result. If the dynamic shear stress ratio is small, the whole part of the soil body is regarded as the area only controlled by the overlying stress, and the whole part of the soil body is adjusted to the central weight - loading area. Otherwise, it is classified into the upstream water - storage area or the downstream seepage area. Supplement the overlying stress influence coefficient and static shear stress influence coefficient obtained from the soil element test into the finite - element parameters and perform dynamic analysis. Output the dynamic shear stress ratio and acceleration results and distinguish them into the central area and its two - side areas.

[0045] The specific content of step S6 is as follows:

[0046] Step S61: First, according to the overlying stress influence coefficient K σ and the static shear stress influence coefficient K α , modify the liquefaction resistance strength of the soil under a specific stress state in the finite - element dynamic analysis according to the following formula to obtain the modified liquefaction resistance strength of the soil:

[0047] CRR' σ，α＝0 =K σ *CRR σ＝100kPa，α＝0

[0048] CRR' σ,α = K α * CRR σ,α＝0

[0049] Wherein, CRR' σ，α＝0 represents the soil liquefaction resistance strength under the overlying effective stress σ when the corrected static shear stress ratio α is taken as 0; CRR σ＝100kPa，α＝0 represents the soil liquefaction resistance strength when the static shear stress ratio α is taken as 0 and the overlying effective stress σ is taken as 100 kPa; CRR' σ,α represents the soil liquefaction resistance strength under the corrected static shear stress ratio α and the overlying effective stress σ;

[0050] The soil element test can obtain the overlying stress influence coefficient K σ and the static shear stress influence coefficient K α under some specific stress states. If the stress state in the finite element dynamic analysis is exactly the same as that in the soil element test, the overlying stress influence coefficient K σ and the static shear stress influence coefficient K α under this stress state are directly used. Otherwise, the overlying stress influence coefficient K σ and the static shear stress influence coefficient K α under this stress state can be determined by linear interpolation.

[0051] Step S62: Then, according to the dynamic shear stress ratio CSR of the soil element, the liquefaction safety factor F of the soil elements in different regions of the dam foundation of the rock-fill dam is obtained by processing according to the following formula s :

[0052] When the soil element is located in the central weight area C:

[0053] When the soil element is located in the upstream water storage area U or the downstream seepage area D:

[0054] Wherein, CSR represents the dynamic shear stress ratio of each soil element in the dam foundation.

[0055] Step S62: Then, according to the region where the soil element is located and the corresponding liquefaction safety factor F s , the liquefaction safety factor contour map of the dam foundation of the rock-fill dam is drawn;

[0056] Step S63: Finally, the seismic liquefaction of the dam foundation of the rock-fill dam is judged according to the liquefaction safety factor contour map of the dam foundation of the rock-fill dam:

[0057] If the liquefaction safety factor Fs is less than 1, it indicates that seismic liquefaction will occur at this position;

[0058] If the liquefaction safety factor Fs is not less than 1, it indicates that seismic liquefaction will not occur at this location.

[0059] The present invention proposes a method for discriminating seismic liquefaction zones of the dam foundation of an earth-rock dam to solve the seismic liquefaction safety analysis during the construction period and service period of the dam foundation of an earth-rock dam in the dam design stage. The in-situ soil of the proposed dam site can be used for in-door unit tests. Through the method combining finite element static and dynamic analysis with unit tests, the seismic liquefaction discrimination of the dam foundation of an earth-rock dam under the influence of different seepage fields is realized, providing a more detailed and specific evaluation framework for the seismic safety and stability of the dam foundation.

[0060] The present invention considers the influence of the seepage field on the initial stress state of the dam foundation under the service state through finite element analysis, which is characterized by the combined variation law of the overlying effective stress and the initial static shear stress, facilitating the full-process safety evaluation of the dam foundation. By dividing the dam foundation into three representative regions: the upstream water storage area (U area), the central weight area (C area), and the downstream seepage area (D area), the present invention fully refines the liquefaction discrimination of the dam foundation, making the discrimination more targeted.

[0061] The beneficial effects of the present invention are as follows:

[0062] 1. The method of the present invention can provide a more comprehensive and reliable framework and approach for the seismic safety analysis of the dam foundation of an earth-rock dam, fully considering the influence of anti-seepage measures on the seepage field and the stress field of the dam foundation, as well as the changes in the stress field of the dam foundation under various working conditions, facilitating the improvement of the full-process evaluation of the liquefaction safety of the dam foundation.

[0063] 2. Through further extended research on the overlying stress correction coefficient and the initial static shear stress correction coefficient, the method of the present invention can more accurately propose the variation law of the dynamic strength of the soil covering layer of a certain type of engineering site, making the liquefaction discrimination more targeted for the engineering site.

[0064] 3. The method of the present invention considers the influence of anti-seepage measures and various working conditions on the stress field of the dam foundation, facilitating the improvement of the full-section and full-process evaluation of the liquefaction safety of the dam foundation, making the anti-liquefaction measures more targeted and regional, and being able to provide concise suggestions for engineering construction. Description of the Drawings

[0065] Figure 1 It is a schematic flow chart of the method for discriminating seismic liquefaction zones;

[0066] Figure 2 It is a schematic diagram of the partition of the dam foundation of an earth-rock dam and the force on the unit body. Detailed Embodiments

[0067] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. The following embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0068] The embodiments of the present invention are as follows, including the following steps, as Figure 1 shown:

[0069] In a specific embodiment, the prototype hypothesis is simplified to a horizontal saturated sandy soil site with a thickness of 100 m. An earth-rock core wall dam with a height of 30 m is designed and constructed on this horizontal site. The relevant dimension design refers to similar earth-rock core wall dam projects. The saturated unit weight is 2000 kg / m 3 , the specific gravity of the sandy soil is 2.65, the coefficient of earth pressure at rest is 0.5, the length of the concrete cut-off wall is 30 m, and the thickness is about 0.28 m. The elevation of the upstream normal storage water level is 28 m; the liquefaction resistance performance of the foundation soil under different seismic loads is evaluated.

[0070] Step S1: First, conduct in-door tests on the soil of the target earth-rock dam foundation, and at the same time, combine relevant geological exploration reports to obtain the basic physical property parameters of the foundation soil; the basic physical property parameters of the foundation soil include the specific gravity, maximum void ratio, minimum void ratio, permeability coefficient, and internal friction angle of the foundation soil;

[0071] For example, the maximum void ratio e of the test soil max = 0.930, and the minimum void ratio e min = 0.519; the material model of the foundation soil can be selected as saturated, and its sandy soil permeability coefficient can be determined to be 5×10 -5 m / s according to relevant geological exploration data;

[0072] Step S2: Based on the basic physical property parameters of the foundation soil, model the whole target earth-rock dam to obtain the finite element model of the target earth-rock dam, and then conduct static finite element analysis on the finite element model to obtain the stress field distribution of the earth-rock dam foundation under different working conditions;

[0073] Specifically in Step S2, determine the overall dimension data of the earth-rock dam body and foundation according to relevant design data, conduct proportional modeling in finite element software, input the parameters for static calculation, and obtain the initial stress distribution field of the earth-rock dam. At this time, it is the initial stress field of the foundation without the influence of the seepage field. After inputting the water level required for the working condition and conducting seepage calculation, then calculate the initial stress field. At this time, the obtained is the initial stress field affected by seepage, which is specifically manifested as the combination of overburden stress and initial static shear stress. The saturated / unsaturated model can be selected for dam body modeling, and its various parameters can be determined according to design data. For example, the saturated permeability coefficient of the core wall can be 5×10-8 m / s, the saturated permeability coefficient of the contact clay can be 1×10 -9 m / s, etc. The normal storage level is set to 28 m according to the design data.

[0074] In step S2, the modeling process of the finite element model corresponding to the target earth-rock dam is as follows:

[0075] Step S2.1: First, construct a finite element model proportionally according to the actual size of the on-site site, and synchronously model the anti-seepage measures in the on-site site. At the same time, set the parameters of the finite element model with the basic physical property parameters of the dam foundation soil obtained in step S1;

[0076] The anti-seepage measures include concrete cut-off walls, composite geomembranes, etc.

[0077] Step S22: Simulate the load conditions of the target earth-rock dam under different working conditions using different water levels. The working conditions of the target earth-rock dam include the construction period and the service period. The service period includes the normal water storage period and the flood period. By changing the water level corresponding to the finite element model, the stress field distribution of the finite element model of the target earth-rock dam during the construction period and the service period can be obtained.

[0078] Step S3: Based on the stress field distribution of the earth-rock dam foundation, conduct a preliminary static force zoning of the earth-rock dam foundation. Specifically, in step S3, according to the initial stress state and the influence brought by the seepage field, it is proposed that with the center axis of the dam foundation as the center, the dam foundation soil is divided into an upstream water storage area (U area), a central weight area (C area), and a downstream seepage area (D area). This is mainly reflected in the change of the initial static shear stress, which will thus affect the liquefaction discrimination.

[0079] The specific steps of step S3 are as follows:

[0080] Step S31: First, according to the stress field distribution of the earth-rock dam foundation, obtain the static shear stress ratio α of each soil element in the dam foundation:

[0081]

[0082] Among them, τ s is the static shear stress of the soil element; σ is the overlying effective stress of the soil element;

[0083] Specifically, the static shear stress τ s and the overlying effective stress σ can be directly obtained from the finite element simulation results.

[0084] Step S32: Next, conduct a preliminary static force zoning on the dam foundation of the earth-rock dam. The dam foundation of the earth-rock dam is divided into three regions: the upstream water storage area U, the central weight area C, and the downstream seepage area D. The upstream water storage area and the downstream seepage area are located on both sides of the central weight area respectively, and the upstream water storage area and the downstream seepage area are located in the upstream area and the downstream area of the earth-rock dam respectively. The zoning method of the dam foundation of the earth-rock dam is determined as follows:

[0085] Compare the static shear stress ratio of each soil element in the dam foundation with a preset static shear stress ratio threshold:

[0086] If the static shear stress ratio of the soil element under all working conditions is less than the static shear stress ratio threshold, it indicates that the soil element is less affected by the static shear stress, and the soil element is classified into the central weight area;

[0087] Otherwise, it indicates that the soil element is more affected by the static shear stress, and the soil element is classified into the upstream water storage area or the downstream seepage area according to the water level line where the soil element is located.

[0088] In step S3, for a horizontal site with an earth-rock dam built, different from a shallow free horizontal site, due to the influence of the initial static shear stress and overlying stress, there are soil elements with different initial stress states in different regions under the dam foundation, and its initial stress state is complex. At the same time, due to the actual situation of water storage in the reservoir area of the dam and the design of cut-off walls, etc., a stable seepage field will be formed inside the dam foundation soil, which further changes the initial stress state of the dam foundation soil area. The initial stress state is specifically characterized by the overlying effective stress and the initial static shear stress, and the distinction of the regional initial stress state is based on different combinations of the overlying effective stress and the initial static shear stress ratio.

[0089] The zoning basis is the difference in the combination and change of the overlying effective stress and the initial shear stress in the region. It is mainly reflected in that due to the influence of dam construction, the dam foundation of the original horizontal site has an initial static shear stress in the regions on both sides of the dam body, while the dam foundation region directly under the dam body has a larger overlying effective stress than that on both sides. The influence of the seepage field during service makes the change of the initial static shear stress upstream and downstream also show differences, so the above zoning is made.

[0090] Step S4: Then conduct soil element tests on the soil of the dam foundation of the earth-rock dam to obtain the overlying stress influence coefficient and the static shear stress influence coefficient of the soil element under different overlying effective stresses and static shear stress ratios;

[0091] In specific implementation, the specific steps of step S4 are as follows:

[0092] Step S41: First, conduct soil element tests on the soil of the dam foundation of the earth-rock dam under different overburden effective stresses σ, obtain the liquefaction resistance strengths of the soil elements under different overburden effective stresses and static shear stress ratios, and obtain the overburden stress influence coefficient K of the soil element under different overburden effective stresses σ according to the following formula σ :

[0093]

[0094] In the formula, K σ represents the overburden stress influence coefficient under the overburden effective stress σ; CRR σ，α＝0 represents the liquefaction resistance strength of the soil under the overburden effective stress σ when the static shear stress ratio α obtained from the soil element test is 0; CRR σ＝100kPa，α＝0 represents the liquefaction resistance strength of the soil when the overburden effective stress σ is 100 kPa and the static shear stress ratio α obtained from the soil element test is 0;

[0095] Step S42: Then, conduct soil element tests on the soil of the dam foundation of the earth-rock dam under different static shear stress ratios α, and obtain the static shear stress influence coefficient K of the soil element under different static shear stress ratios α through the following formula processing α :

[0096]

[0097] In the formula, K α represents the static shear stress influence coefficient under the static shear stress ratio α; CRR σ,α represents the liquefaction resistance strength of the soil under the static shear stress ratio α and the overburden effective stress σ obtained from the soil element test.

[0098] Step S4 specifically designs the element test scheme according to the initial stress state, conducts relevant dynamic strength tests aiming at studying the overburden stress influence coefficient and the static shear stress influence coefficient, and obtains the correction coefficients at each relevant stress level. In the embodiment, the dynamic strength of 15 cycles of liquefaction of the soil at a certain place with a confining pressure of 100 kPa can be obtained to be about 0.25, the overburden stress correction coefficient K σ = 1, and the initial static shear stress influence coefficient K α = 1.05.

[0099] Step S5: Next, update the parameters of the finite element model of the earth-rock dam according to the overburden stress influence coefficient and the static shear stress influence coefficient in Step S4, conduct dynamic analysis on the updated finite element model, and rezone the dam foundation of the earth-rock dam according to the dynamic analysis results;

[0100] Step S5 is specifically as follows:

[0101] Step S51: First, set the parameters of the finite element model of the rock-fill dam according to the overburden stress influence coefficient and static shear stress influence coefficient obtained in Step S4. Specifically, substitute the overburden stress influence coefficient and static shear stress influence coefficient obtained in Step S4 into the finite element model of the rock-fill dam;

[0102] Overburden stress influence coefficient K σ For parameter setting of the central weight area C of the preliminary static zoning, static shear stress influence coefficient K α For parameter setting of the upstream water storage area U and downstream seepage area D of the preliminary static zoning;

[0103] Step S52: Then, input the seismic wave for seismic liquefaction dynamic analysis into the finite element model with updated parameters. The seismic wave adopts a 15-cycle equal-amplitude sine wave, and the maximum acceleration amplitude of the seismic wave adopts the actual maximum acceleration amplitude of the site. In the output equal-amplitude sine wave time history curve, the acceleration amplitude at the end of the seismic wave time history is set to zero, which can more approximately simulate the post-failure response of the vibration subsiding;

[0104] Step S53: Then, conduct seismic liquefaction dynamic analysis on the finite element model input with the seismic wave to obtain the effective overburden stress σ' v and dynamic shear stress τ av of the finite element model under the action of the seismic wave, and process them according to the following formula to obtain the cyclic stress ratio CSR of each soil element in the dam foundation:

[0105]

[0106] where τ av is the dynamic shear stress of the soil element; σ' v is the effective overburden stress of the soil element;

[0107] Step S54: Then, re-conduct dynamic zoning on the dam foundation of the rock-fill dam according to the cyclic stress ratio CSR of the soil element. The dynamic zoning method of the dam foundation of the rock-fill dam is determined as follows:

[0108] Compare the cyclic stress ratio of each soil element in the dam foundation with the preset cyclic stress ratio threshold:

[0109] If the cyclic stress ratio of the soil element under all working conditions is less than the cyclic stress ratio threshold, it indicates that the soil element is less affected by the dynamic shear stress, and the soil element is classified into the central weight area;

[0110] Otherwise, it indicates that the soil element is more affected by the dynamic shear stress. According to the water level line where the soil element is located, the soil element is classified into the upstream water storage area or the downstream seepage area. Among them, the re-zoned upstream water storage area and downstream seepage area are located in the upstream area and downstream area of the rock-fill dam respectively.

[0111] Adjust the static force zoning result according to the finite element simulation result. If the dynamic shear stress is relatively small, consider each part of the soil mass as the area only controlled by the overlying stress, and adjust each part of the soil mass as the central weight area. Otherwise, divide it into the upstream water storage area or the downstream seepage area. Supplement the overlying stress influence coefficient and static shear stress influence coefficient obtained from the soil element test into the finite element parameters and conduct dynamic analysis. Output the dynamic shear stress ratio and acceleration results and distinguish them into the central area and its two sides areas.

[0112] Step S5 is specifically to input seismic waves for dynamic calculation to obtain the variation law of dynamic shear stress in different zones. The input seismic waves are approximated by 15 - cycle equal - amplitude sine waves, with an amplitude of 0.2g, an action frequency of 1Hz, an action period of 15s, and an end - calming period of 15s. It can be calculated that the dynamic shear stress ratio of a certain soil mass is about 0.45.

[0113] Step S6: Conduct liquefaction discrimination on the dam foundation of the rock - fill dam according to the zoning result obtained in step S5, and obtain the liquefaction discrimination result of the target rock - fill dam foundation.

[0114] Among them, step S6 is specifically as follows:

[0115] Step S61: First, according to the overlying stress influence coefficient K σ and the static shear stress influence coefficient K α in step S4, correct the liquefaction resistance strength of the soil under a specific stress state in the finite element dynamic analysis according to the following formula to obtain the corrected liquefaction resistance strength of the soil:

[0116] CRR' σ，α＝0 =K σ *CRR σ＝100kPa，α＝0

[0117] CRR' σ,α =K α *CRR σ,α＝0

[0118] Among them, CRR' σ，α＝0 represents the liquefaction resistance strength of the soil under the overlying effective stress σ when the corrected static shear stress ratio α is 0; CRR σ＝100kPa，α＝0 represents the liquefaction resistance strength of the soil under the overlying effective stress σ of 100kPa when the static shear stress ratio α obtained from the dynamic analysis of the finite element model is 0; CRR' σ,α represents the liquefaction resistance strength of the soil under the corrected static shear stress ratio α and the overlying effective stress σ;

[0119] The soil element test can obtain the overlying stress influence coefficient K σ and the static shear stress influence coefficient Kα , if the stress state in the finite element dynamic analysis is exactly the same as that in the soil element test, the overburden stress influence coefficient K under this stress state is directly used σ and the static shear stress influence coefficient K α , otherwise, the overburden stress influence coefficient K under this stress state can be determined by linear interpolation σ and the static shear stress influence coefficient K α

[0120] Step S62: Then, according to the dynamic shear stress ratio CSR of the soil element, the anti-liquefaction safety factor F of the soil elements in different regions of the dam foundation of the rockfill dam is obtained by the following formula s :

[0121] When the soil element is located in the central weight-loading area C:

[0122] When the soil element is located in the upstream water storage area U or the downstream seepage area D:

[0123] Among them, CSR represents the dynamic shear stress ratio of each soil element in the dam foundation.

[0124] The anti-liquefaction strength of the soil is obtained according to the test results of the soil element test. Through the corresponding anti-liquefaction strengths of the soils in the three regions of the upstream water storage area U, the central weight-loading area C, and the downstream seepage area D and the dynamic shear stress ratio CSR of the soil element, the distribution law of the soil liquefaction safety factor of the whole dam foundation is obtained;

[0125] Step S62: Then, according to the region where the soil element is located and the corresponding anti-liquefaction safety factor F s , the liquefaction safety factor contour map of the dam foundation of the rockfill dam is drawn;

[0126] Step S63: Finally, the seismic liquefaction of the dam foundation of the rockfill dam is judged according to the liquefaction safety factor contour map of the dam foundation of the rockfill dam:

[0127] If the liquefaction safety factor Fs is less than 1, it indicates that seismic liquefaction will occur at this position;

[0128] If the liquefaction safety factor Fs is not less than 1, it indicates that seismic liquefaction will not occur at this position.

[0129] Subsequently, the design scheme of the dam foundation of the rockfill dam can be optimized according to the liquefaction safety factor Fs of the dam foundation of the rockfill dam.

[0130] Step S6 is to make a judgment using the corresponding liquefaction discrimination criteria. In this embodiment, the liquefaction safety factor can be referred to for use, but it is not limited to this method. According to the modified soil anti-liquefaction strength in different zones of the dam foundation soil and the dynamic shear stress ratio CSR in different zones that have been obtained, the anti-liquefaction safety factor Fs is obtained by using the soil anti-liquefaction strength and the dynamic shear stress ratio. If Fs is greater than 1, it means that the soil anti-liquefaction strength is greater than the dynamic shear stress ratio, that is, this part of the soil in the dam foundation will not liquefy under this dynamic load. On the contrary, if the anti-liquefaction safety factor is less than 1, there is a liquefaction risk. In step S6, according to the modified soil anti-liquefaction strength at a certain place in the dam foundation obtained in step S4, the final value is 0.26, and the dynamic shear stress ratio CSR at this place obtained from step S5 is 0.45, then F s = 0.58 < 1, and it can be preliminarily judged that there is a liquefaction risk here under similar earthquake actions.

[0131] Similarly, the points in each part of the dam foundation can be calculated to obtain the safety factors at each place in the three typical areas of the upstream water storage area U, the central weight area C, and the downstream seepage area D of the dam foundation as shown in Figure 2 . In the figure, τ d is the dynamic shear stress, τ s1 and τ s2 are the initial static shear stresses at the upstream and downstream respectively, and σ ωU , σ ωC , σ ωD are the normal stresses of the upstream water storage area U, the central weight area C, and the downstream seepage area D respectively. Under different working conditions, the overall liquefaction safety analysis of the dam foundation is finally formed, and the liquefaction safety factor contour map is output.

[0132] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for discriminating seismic liquefaction zoning of the foundation of an earth-rock dam, characterized in that, It includes the following steps: Step S1: First, conduct indoor tests on the soil of the target earth-rock dam foundation to obtain the basic physical property parameters of the foundation soil. The basic physical property parameters of the foundation soil include the specific gravity, maximum void ratio, minimum void ratio, permeability coefficient, and internal friction angle of the foundation soil; Step S2: Based on the basic physical property parameters of the foundation soil, model the entire target earth-rock dam to obtain a finite element model, and then conduct static finite element analysis on the finite element model to obtain the stress field distribution of the earth-rock dam foundation under different working conditions; Step S3: According to the stress field distribution of the earth-rock dam foundation, conduct a preliminary static zoning of the earth-rock dam foundation; Step S4: Then conduct soil element tests on the soil of the earth-rock dam foundation to obtain the overburden stress influence coefficient and static shear stress influence coefficient of the soil element under different effective overburden stresses and static shear stress ratios; Step S5: Next, update the parameters of the finite element model of the earth-rock dam according to the overburden stress influence coefficient and static shear stress influence coefficient in Step S4, conduct dynamic analysis on the updated finite element model, and rezone the earth-rock dam foundation according to the dynamic analysis results; Step S6: Conduct liquefaction discrimination on the earth-rock dam foundation according to the zoning results obtained in Step S5 to obtain the liquefaction discrimination results of the target earth-rock dam foundation.

2. A method for discriminating seismic liquefaction zoning of the foundation of an earth-rock dam according to claim 1, characterized in that: In Step S2, the modeling process of the finite element model corresponding to the target earth-rock dam is as follows: Step S2.1: First, construct a finite element model in proportion according to the actual size of the on-site site, and simultaneously model the anti-seepage measures in the on-site site. At the same time, set the parameters of the finite element model with the basic physical property parameters of the foundation soil obtained in Step S1; Step S22: Use different water levels to simulate the load conditions of the target earth-rock dam under different working conditions. The working conditions of the target earth-rock dam include the construction period and the service period. By changing the water level corresponding to the finite element model, obtain the stress field distribution of the finite element model of the target earth-rock dam during the construction period and the service period.

3. A method for discriminating seismic liquefaction zoning of the foundation of an earth-rock dam according to claim 1, characterized in that: The specific content of Step S3 is as follows: Step S31: First, according to the stress field distribution of the earth-rock dam foundation, obtain the static shear stress ratio α of each soil element in the foundation; Among them, τ s is the static shear stress of the soil element; σ is the overlying effective stress of the soil element; Step S32: Then conduct a preliminary static zoning of the earth-rock dam foundation. The earth-rock dam foundation is divided into three regions: the upstream water storage area U, the central weight area C, and the downstream seepage area D. The upstream water storage area and the downstream seepage area are located on both sides of the central weight area respectively, and the upstream water storage area and the downstream seepage area are located in the upstream area and the downstream area of the earth-rock dam respectively. The zoning method of the earth-rock dam foundation is determined as follows: Compare the static shear stress ratio of each soil element in the foundation with a preset static shear stress ratio threshold: If the static shear stress ratio of the soil element under all working conditions is less than the static shear stress ratio threshold, it indicates that the soil element is less affected by the static shear stress, and the soil element is divided into the central weight area; Otherwise, it indicates that the soil element is more affected by the static shear stress, and the soil element is divided into the upstream water storage area or the downstream seepage area according to the water level line where the soil element is located.

4. A method for discriminating seismic liquefaction zoning of the foundation of an earth-rock dam according to claim 1, characterized in that: The specific content of Step S4 is as follows: Step S41: First, under different overburden effective stresses σ, conduct soil element tests on the soil of the dam foundation of the earth-rock dam, and obtain the overburden stress influence coefficient K of the soil element under different overburden effective stresses σ according to the following formula σ :[[]]END]] Where K σ represents the overburden stress influence coefficient under the overburden effective stress σ; CRR σ，α＝0 represents the soil liquefaction resistance strength under the overburden effective stress σ when the static shear stress ratio α is 0; CRR σ＝100kPa，α＝0 represents the soil liquefaction resistance strength when the static shear stress ratio α is 0 and the overburden effective stress σ is 100 kPa; Step S42: Then, under different static shear stress ratios α, perform soil element tests on the soil of the dam foundation of the earth-rock dam, and obtain the static shear stress influence coefficient K of the soil element under different static shear stress ratios α by processing according to the following formula α : where K α represents the static shear stress influence coefficient under the static shear stress ratio α; CRR σ,α represents the soil liquefaction resistance strength under the static shear stress ratio α and the overlying effective stress σ.

5. A method for discriminating seismic liquefaction zoning of the foundation of an earth-rock dam according to claim 1, characterized in that: The specific content of Step S5 is as follows: Step S51: First, set the parameters of the finite element model of the earth-rock dam according to the overburden stress influence coefficient and static shear stress influence coefficient obtained in Step S4; The overburden stress influence coefficient K σ is used to set parameters for the central weight area C of the preliminary static force partition, and the static shear stress influence coefficient K α is used to set parameters for the upstream water storage area U and the downstream seepage area D of the preliminary static force partition; Step S52: Then, input the seismic wave for seismic liquefaction dynamic analysis into the finite element model with updated parameters. The seismic wave adopts an equal-amplitude sine wave, and the maximum acceleration amplitude of the seismic wave adopts the actual maximum acceleration amplitude of the on-site site; Step S53: Next, perform seismic liquefaction dynamic analysis on the finite element model of the input seismic wave to obtain the overlying effective stress σ' of the finite element model under the action of the seismic wave v and the dynamic shear stress τ av , and process them according to the following formula to obtain the dynamic shear stress ratio CSR of each soil element in the dam foundation: where τ av is the dynamic shear stress of the soil element; σ' v is the overlying effective stress of the soil element; Step S54: Then, re-perform dynamic zoning on the dam foundation of the earth-rock dam according to the dynamic shear stress ratio CSR of the soil element. The dynamic zoning method of the dam foundation of the earth-rock dam is determined as follows: Compare the dynamic shear stress ratio of each soil element in the dam foundation with the preset dynamic shear stress ratio threshold: If the dynamic shear stress ratio of the soil element under all working conditions is less than the dynamic shear stress ratio threshold, it indicates that the soil element is less affected by the dynamic shear stress, and the soil element is divided into the central weight-loading area; Otherwise, it indicates that the soil element is more affected by the dynamic shear stress, and the soil element is divided into the upstream water storage area or the downstream seepage area according to the water level line where the soil element is located.

6. A method for discriminating seismic liquefaction zoning of the foundation of an earth-rock dam according to claim 1, characterized in that: The specific content of Step S6 is as follows: Step S61: First, according to the overburden stress influence coefficient K σ and the static shear stress influence coefficient K α , the soil liquefaction resistance strength in the finite element dynamic analysis is corrected according to the following formula to obtain the corrected soil liquefaction resistance strength: CRR' σ，α＝0 = K σ * CRR σ＝100kPa，α＝0 CRR' σ,α = K α * CRR σ,α＝0 Among them, CRR' σ，α＝0 represents the liquefaction resistance of the soil under the overlying effective stress σ when the corrected static shear stress ratio α is 0; CRR σ＝100kPa，α＝0 represents the liquefaction resistance of the soil when the static shear stress ratio α is 0 and the overlying effective stress σ is 100 kPa; CRR' σ,α represents the liquefaction resistance of the soil under the corrected static shear stress ratio α and the overlying effective stress σ; Step S62. Then, according to the dynamic shear stress ratio CSR of the soil element, the liquefaction resistance safety factor F of the soil elements in different regions of the dam foundation of the earth-rock dam is obtained by processing according to the following formula s : When the soil element is located in the central weight-loading area C: When the soil element is located in the upstream storage area U or the downstream seepage area D: Among them, CSR represents the dynamic shear stress ratio of each soil element in the dam foundation; Step S62. Then, according to the region where the soil element is located and the corresponding liquefaction safety factor F s , a liquefaction safety factor contour map of the dam foundation of the earth-rock dam is drawn; Step S63: Finally, determine the seismic liquefaction of the dam foundation of the earth-rock dam according to the liquefaction safety factor contour map of the dam foundation of the earth-rock dam: If the liquefaction safety factor Fs is less than 1, it indicates that seismic liquefaction will occur at this location; If the liquefaction safety factor Fs is not less than 1, it indicates that seismic liquefaction will not occur at this location.

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