Dam foundation liquefaction earthquake damage risk assessment method based on probability analysis

Abstract

The invention discloses a dam foundation liquefaction earthquake damage risk assessment method based on probability analysis. The method comprises the steps that on the basis of an on-site earthquake safety evaluation report, under the condition that the compaction effect of a gravel pile on a dam foundation and the effect of overlying stress on crustal stress increase are considered, dam foundation surface earthquake oscillation parameter danger curves under different working conditions are established; drawing a soil body parameter space distribution diagram of the dam foundation soil body under different working conditions; then selecting a proper liquefaction earthquake damage simplified calculation model; and performing dam foundation liquefaction earthquake damage analysis by combining a liquefaction earthquake damage simplified calculation model according to the dam foundation surface seismic oscillation parameter danger curve and the soil mass parameter spatial distribution diagram, obtaining seismic liquefaction probability distribution diagrams of each layer of soil mass under different working conditions, and evaluating the seismic liquefaction risk of the soil mass according to the seismic liquefaction probability distribution diagrams. According to the method, the aseismic design and risk management of the dam foundation can be effectively guided, the uncertainty of earthquake, geology and soil parameters can be more comprehensively considered, and the safety and reliability of water conservancy projects can be improved.

Description

Technical Field

[0001] The invention belongs to the field of identification of liquefaction of saturated sand dam foundations in thick overburden layers of earthquake sites, and specifically relates to a method for assessing earthquake damage risk of dam foundation liquefaction based on probability analysis. Background Art

[0002] Directly building earth-rock dams on deep overburden in high-intensity earthquake zones has become a common form of water resource development and utilization in western my country. The liquefaction phenomenon caused by earthquakes is one of the important reasons for the instability and destruction of dam foundations. Historical earthquake events have shown that liquefaction can lead to significant ground subsidence, cracking, and uneven settlement of the dam body, thus causing serious engineering disasters. For earth-rock dams built on deep overburden, the dam body is large in scale, the spatial span of the dam foundation bearing layer soil is large, the dam foundation soil type and its distribution are complex and random, and the soil physical and mechanical parameters have strong spatial variability; at the same time, the inconsistency of seismic wave propagation and the terrain effect cause the seismic waves in the site to present complex reflection, refraction, and focusing effects, and the seismic motion parameter hazard curve changes with time and space.

[0003] Traditional dam foundation liquefaction risk assessment methods are mainly based on deterministic analysis. Deterministic dam foundation liquefaction risk assessment algorithms are widely used due to their simplicity and normative support. These methods are usually based on some empirical or semi-empirical methods, using the physical properties of soil and data from historical earthquake events to assess the possibility and potential impact of liquefaction. The spatial variability of soil physical and mechanical parameters and the uncertainty of ground motion are not considered. The determined soil parameter values ​​are generally conservative, and the assumptions about external effects such as dam construction, water storage service and earthquakes are too extreme. Therefore, the deterministic analysis method may lead to a large deviation in the risk of dam foundation liquefaction, and has little reference value for the anti-liquefaction design of earth-rock dams.

[0004] In view of the complexity and uncertainty of earthquake liquefaction, it is particularly important to use probabilistic analysis methods to assess the risk of dam foundation liquefaction damage. Probabilistic analysis can quantify the possibility of liquefaction and the damage it may cause, providing a more scientific and reasonable basis for risk management and decision-making. In order to carry out more reasonable anti-liquefaction design, considering the spatial variability of soil physical and mechanical parameters and the uncertainty of seismic motion, it is urgent to propose a new spatial analysis method for dam foundation liquefaction damage risk. Summary of the invention

[0005] In order to solve the problems existing in the background technology, the purpose of the present invention is to provide a dam foundation liquefaction seismic risk assessment method based on probability analysis to solve the problem that the existing dam foundation liquefaction risk assessment method cannot reasonably consider the uncertainty of earthquake, geological and soil parameters.

[0006] The technical solution adopted by the present invention is as follows, comprising the following steps:

[0007] Step S1: First, based on the on-site earthquake safety assessment report, considering the compaction effect of gravel piles on the dam foundation and the effect of overburden stress on ground stress increase, establish the dam foundation surface seismic parameter hazard curve under different working conditions;

[0008] Step S2: Next, draw a spatial distribution diagram of soil parameters of the dam foundation soil under different working conditions;

[0009] Step S3, then selecting an appropriate simplified calculation model for liquefaction damage according to site conditions and centrifuge shaking table model tests;

[0010] Step S4: Based on the dam foundation seismic parameter hazard curve in step S1 and the soil parameter spatial distribution map obtained in step S2, combined with the simplified calculation model of liquefaction seismic damage, Monte Carlo simulation is used in geographic information analysis software GIS to perform spatial analysis of dam foundation liquefaction seismic damage, and the mean distribution map and variance distribution map of the seismic liquefaction probability of each layer of soil in the site under different working conditions are obtained;

[0011] Step S5: Finally, using the earthquake liquefaction probability P l The mean distribution diagram and variance distribution diagram of the soil are used to evaluate the seismic liquefaction risk of each layer of soil in the site under different real working conditions.

[0012] The step S1 specifically includes the following steps:

[0013] Step S1.1, according to the annual average exceedance probability of the bedrock horizontal peak acceleration in the earthquake safety assessment report, draw a bedrock seismic parameter hazard curve, wherein the ordinate of the bedrock seismic parameter hazard curve is the bedrock horizontal peak acceleration, and the abscissa is the annual average exceedance probability corresponding to the bedrock horizontal peak acceleration;

[0014] Step S1.2, construct a dam foundation-bedrock model, use gravel piles, overburden stress and water level to simulate the external environment of the dam foundation-bedrock model under different working conditions, and obtain the dam foundation-bedrock model under different working conditions; then, perform numerical simulation or centrifuge vibration table model test on the dam foundation-bedrock model under different working conditions, and combine with the bedrock seismic motion parameter hazard curve to draw the dam foundation surface seismic motion parameter hazard curve under different working conditions, the ordinate of the dam foundation surface seismic motion parameter hazard curve is the horizontal peak acceleration of the dam foundation surface, and the abscissa is the annual average exceedance probability corresponding to the horizontal peak acceleration of the dam foundation surface.

[0015] The step S2 is specifically as follows:

[0016] Step S2.1: First, obtain the location of each drilling point in the site, and then conduct geotechnical tests on the soil at each drilling point to obtain the soil layer thickness d and groundwater level z of each soil layer at each drilling point. w, and the mean and variance of soil static and dynamic parameters, wherein the soil static and dynamic parameters include soil density ρ and shear wave velocity V s , the mean value and variance of the static and dynamic parameters of the soil layer are obtained by respectively calculating the mean value and variance of the static and dynamic parameters of the soil at different depths in the same soil layer;

[0017] Step S2.2: calculate the soil thickness d and groundwater level z of each soil layer at each drilling point. w The mean and variance of the static and dynamic parameters of the soil are imported into the geographic information analysis software GIS. The Kriging interpolation method in the geographic information analysis software GIS is used to obtain the soil layer thickness d and groundwater level z of each soil layer at all locations of the site. w , and the mean and variance of soil static and dynamic parameters, and draw a spatial distribution map of soil parameters for each soil layer in a natural site, wherein the spatial distribution map of soil parameters includes a soil layer thickness distribution map, a groundwater level distribution map, a mean distribution map of soil static and dynamic parameters, and a variance distribution map of soil static and dynamic parameters;

[0018] Step S2.3, construct a natural dam foundation-bedrock model, use gravel piles, overburden stress and water level to simulate the external environment of the dam foundation-bedrock model under different working conditions, so as to obtain the dam foundation-bedrock model under different working conditions; then, perform numerical simulation or centrifuge vibration table model test on the dam foundation-bedrock model under different working conditions, and combine the soil parameter distribution map of each soil layer in the natural site obtained in step S2.2 to obtain the spatial distribution map of soil parameters of each soil layer in the site under different working conditions.

[0019] In step S3, the simplified calculation model of liquefaction damage is expressed as follows:

[0020]

[0021]

[0022]

[0023]

[0024] Among them, P l represents the probability of earthquake liquefaction of the soil layer; FS represents the safety factor against liquefaction of the soil layer; CRR represents the cyclic stress ratio of the soil layer, and CSR represents the cyclic resistance ratio of the soil layer; a max is the horizontal peak acceleration of the dam base; g is the gravitational acceleration; σ vc is the total vertical stress on the soil layer; σ vc ' is the overlying effective stress; γ d V is the stress stiffness reduction factor of the soil layer; s1 is the shear wave velocity corrected for overburden stress; Vs1 ' is the upper limit shear wave velocity of soil liquefaction. When the average clay content FC≤5%, V s1 'Take 215m / s, when FC≥35%, V s1 'Take 200m / s; when 5%<FC<35%, V s1 'It can be calculated by linear interpolation; MSF represents the magnitude scale factor.

[0025] The step S4 is specifically as follows: first, the dam foundation seismic parameter hazard curve in step S1 and the soil parameter spatial distribution map obtained in step S2 are input into the geographic information analysis software GIS, and the simplified calculation model of liquefaction seismic damage in step S3 is selected in the geographic information analysis software GIS. The simplified calculation model of liquefaction seismic damage is based on the input horizontal peak acceleration of the dam foundation, the soil layer thickness d, and the groundwater level z. w , and soil static and dynamic parameter processing combined with Monte Carlo simulation to obtain the seismic liquefaction probability P of the soil layer l According to the mean and variance of the seismic liquefaction probability of each soil layer at all locations on the site under different working conditions, the mean distribution diagram and variance distribution diagram of the seismic liquefaction probability under different working conditions are drawn respectively.

[0026] Monte Carlo simulation is a numerical method based on random sampling. It estimates the probability distribution of the results and its statistical characteristics by simulating the system behavior under different input conditions multiple times.

[0027] The working conditions of the dam foundation-bedrock model include the gravel pile construction period, the dam building period and the dam body service and water storage period. The dam foundation-bedrock model during the gravel pile construction period is obtained by simulating by applying gravel piles to the dam foundation in the natural dam foundation-bedrock model. The dam foundation-bedrock model during the dam building period is obtained by simulating by applying a given overburden stress on the dam foundation surface of the dam foundation-bedrock model during the gravel pile construction period. The dam foundation-bedrock model during the dam body service and water storage period is obtained by simulating by applying a given water level to the dam foundation-bedrock model during the dam building period.

[0028] In the simplified calculation model of liquefaction damage, the stress stiffness reduction factor γ of the soil layer is d According to the following formula:

[0029]

[0030] Where z represents the average depth of the soil layer;

[0031] Shear wave velocity V after overburden stress correction s1 The expressions of the magnitude scale factor MSF are as follows:

[0032]

[0033]

[0034] Where V s is the shear wave velocity; P a is atmospheric pressure; M w is the moment magnitude.

[0035] The present invention takes into account the uncertainty of earthquake motion and the spatial variability of soil parameters, and uses numerical simulation or centrifuge shaking table model test to study the influence of terrain effect, inconsistency of earthquake motion, and high overlying stress on the static and dynamic parameters of dam foundation soil, as well as the evolution of mechanical properties of the gravel pile treatment area of ​​the dam foundation. The mean and variance of each parameter at different drilling points and different depths are statistically analyzed, and the probability spatial distribution of parameters such as soil thickness, groundwater level, soil density, and shear wave velocity is established in GIS. The limitation of the original deterministic earthquake liquefaction assessment method for sandy soil that cannot be applied to dam foundations with deep overburden is overcome, and the dam foundation liquefaction earthquake damage risk is accurately analyzed in space, thereby improving the accuracy and effectiveness of earthquake liquefaction risk assessment of dam foundation soil with deep overburden.

[0036] The method of the present invention relates to the field of liquefaction identification of saturated sand soil dam foundations with deep overburden at earthquake sites, and aims to comprehensively consider the uncertainty of earthquake motion, the spatial variability of soil parameters of the dam foundation overburden layer, and the changes in external conditions such as gravel pile construction, dam construction and water storage, so as to effectively evaluate the risk of dam foundation liquefaction. The method uses a probability analysis method to construct a hazard curve of earthquake motion parameters of the dam foundation surface that changes with time; establishes a spatiotemporal distribution probability model of static and dynamic parameters of the dam foundation overburden layer soil; combines a simplified calculation model for liquefaction damage, establishes a probability analysis-based liquefaction damage risk assessment algorithm, conducts spatial analysis of dam foundation liquefaction damage, and draws a dam foundation earthquake liquefaction risk map.

[0037] The beneficial effects of the present invention are:

[0038] 1. The probability analysis of the earthquake motion parameter hazard curve of the present invention can quantify the possibility of liquefaction and more comprehensively evaluate the risk of dam foundation liquefaction damage.

[0039] 2. The present invention takes into account the uncertainty of seismic motion and the spatial variability of soil parameters, and uses numerical simulation or centrifuge shaking table model tests to study the influence of terrain effects, inconsistency of seismic motion, and high overlying stress on the static and dynamic parameters of dam foundation soil, as well as the evolution of mechanical properties of the gravel pile treatment area of ​​the dam foundation, so as to obtain the static and dynamic parameters of the dam foundation under different working conditions (periods), overcoming the limitation that the original deterministic seismic liquefaction assessment method for sand cannot be applied to dam foundations with deep overburden.

[0040] 3. The method of the present invention conducts accurate spatial analysis of the risk of dam foundation liquefaction and introduces the mean and variance of soil static and dynamic parameters, which can effectively guide the seismic design and risk management of the dam foundation, and can more comprehensively consider the uncertainties of earthquake, geological and soil parameters, providing a more scientific and accurate means of assessing the risk of dam foundation liquefaction and seismic damage, which is helpful to improve the safety and reliability of water conservancy projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is the flow chart of the spatial analysis method of dam foundation liquefaction seismic damage risk;

[0042] Figure 2 This is an example diagram of the earthquake liquefaction risk of the dam foundation of each soil layer during the gravel pile construction period in the specific example of the present invention. DETAILED DESCRIPTION

[0043] The present invention is described in detail below in conjunction with specific implementation cases. The following implementation cases will help those skilled in the art to further understand the present invention, but will not limit the present invention in any form.

[0044] A method for assessing the risk of dam foundation liquefaction damage based on probability analysis is proposed. The main technical idea is to use numerical simulation or centrifuge shaking table model test to study the terrain effect and inconsistency of earthquake motion, the influence of high overburden stress on the static and dynamic parameters of dam foundation soil, and the evolution of mechanical properties of the gravel pile treatment area of ​​the dam foundation. When drawing GIS, based on the mean and variance distribution diagram of soil parameters, combined with the Monte Carlo simulation method, the uncertainty of earthquake motion and the spatiotemporal variability of soil parameters are considered to obtain the mean and variance distribution diagram of the liquefaction risk index.

[0045] like Figure 1 As shown, the steps of the embodiment of the present invention are as follows:

[0046] like Figure 1 As shown in the flow chart, the method of the present invention comprises the following steps:

[0047] Step S1, collecting earthquake history records, geological survey reports and geotechnical test data of the bedrock in the dam site area; arranging the collected earthquake history records into an earthquake safety assessment report, and establishing a dam foundation surface seismic motion parameter hazard curve under different working conditions based on the earthquake safety assessment report, taking into account the compaction effect of gravel piles on the dam foundation and the effect of overburden stress on ground stress increase;

[0048] Step S2: Next, draw a spatial distribution diagram of soil parameters of the dam foundation soil under different working conditions;

[0049] Step S3, then selecting an appropriate simplified calculation model for liquefaction damage according to site conditions and centrifuge shaking table model tests;

[0050] Step S4: Based on the dam foundation seismic parameter hazard curve in step S1 and the soil parameter spatial distribution map obtained in step S2, combined with the simplified calculation model of liquefaction seismic damage, Monte Carlo simulation is used in geographic information analysis software GIS to perform spatial analysis of dam foundation liquefaction seismic damage, and the mean distribution map and variance distribution map of the seismic liquefaction probability of each layer of soil in the site under different working conditions are obtained;

[0051] Step S5: Finally, using the earthquake liquefaction probability P l The mean distribution diagram and variance distribution diagram of the soil are used to evaluate the seismic liquefaction risk of each layer of soil in the site under different working conditions.

[0052] Step S5.1: The probability of dam foundation liquefaction under various working conditions generated according to the above steps P l The mean distribution diagram and variance distribution diagram of the dam foundation are used to evaluate the liquefaction situation. The evaluation principles are as follows:

[0053] 0≤P l <0.3, no liquefaction;

[0054] 0.3≤P l <0.7, possible liquefaction;

[0055] 0.7≤P l <1.0, liquefaction;

[0056] Step S5.2: Combine the evaluation results of step S5.1 and focus on the liquefaction position (0.7≤P l <1.0), and propose reinforcement measures and earthquake emergency management plans.

[0057] Step S1 specifically includes the following steps:

[0058] Step S1.1, according to the annual average exceedance probability of the bedrock horizontal peak acceleration in the earthquake safety assessment report, draw a bedrock seismic parameter hazard curve, the ordinate of the bedrock seismic parameter hazard curve is the bedrock horizontal peak acceleration, and the abscissa is the annual average exceedance probability corresponding to the bedrock horizontal peak acceleration;

[0059] Step S1.2, construct a dam foundation-bedrock model, use gravel piles, overburden stress and water level to simulate the external environment of the dam foundation-bedrock model under different working conditions, and obtain the dam foundation-bedrock model under different working conditions; then, perform numerical simulation or centrifuge vibration table model test on the dam foundation-bedrock model under different working conditions, and combine with the bedrock seismic motion parameter hazard curve to draw the dam foundation surface seismic motion parameter hazard curve under different working conditions, the ordinate of the dam foundation surface seismic motion parameter hazard curve is the horizontal peak acceleration of the dam foundation surface, and the abscissa is the annual average exceedance probability corresponding to the horizontal peak acceleration of the dam foundation surface.

[0060] Specifically, gravel piles are added to the dam foundation in the natural dam foundation-bedrock model, which can be used to simulate the compaction effect of gravel piles on the dam foundation, and then the dam foundation-bedrock model during the gravel pile construction period is obtained. By numerically simulating or centrifuge shaking table model tests on the dam foundation-bedrock model under the above different working conditions, the propagation law of seismic acceleration with different annual average exceedance probabilities under different working conditions in the dam foundation soil can be obtained, and then the peak earthquake acceleration at the dam foundation surface under different working conditions can be obtained based on the propagation law of seismic acceleration in the dam foundation soil, and the hazard curve of seismic parameters of the dam foundation surface can be drawn.

[0061] Step S2 is specifically as follows:

[0062] Step S2.1: First, obtain the location of each drilling point in the site, and then conduct geotechnical tests on the soil at each drilling point to obtain the soil layer thickness d and groundwater level z of each soil layer at each drilling point. w , and the mean and variance of soil static and dynamic parameters, including soil density ρ and shear wave velocity V s , the mean and variance of the static and dynamic parameters of the soil layer are obtained by calculating the mean and variance of the static and dynamic parameters of the soil at different depths in the same soil layer;

[0063] Geotechnical test data include soil thickness d, groundwater level z w , soil density ρ, shear wave velocity V s Parameters such as soil thickness z and groundwater level z w Generally, it is directly obtained from the borehole data. The soil density ρ and shear wave velocity Vs are generally obtained from multiple groups of indoor and outdoor tests. These soil parameters obtained from different borehole points and different depths are statistically analyzed to obtain the mean and variance of the soil density ρ and shear wave velocity Vs of soil layers at different borehole points and different depths. These are imported into GIS and Kriging interpolation is used to generate the mean and variance distribution map of the natural dam foundation soil parameters of soil layers at different depths.

[0064] Step S2.2: calculate the soil thickness d and groundwater level z of each soil layer at each drilling point. w The mean and variance of the static and dynamic parameters of the soil are imported into the geographic information analysis software GIS. The Kriging interpolation method in the geographic information analysis software GIS is used to obtain the soil layer thickness d and groundwater level z of each soil layer at all locations of the site. w , as well as the mean and variance of soil static and dynamic parameters, and draw the spatial distribution map of soil parameters of each soil layer in the natural site. The spatial distribution map of soil parameters includes soil layer thickness distribution map, groundwater level distribution map, soil static and dynamic parameter mean distribution map and soil static and dynamic parameter variance distribution map;

[0065] Specifically, the soil parameter distribution map is an RGB two-dimensional image, and each pixel in the image is used to represent the horizontal position of each soil layer in the site, and the color is used to represent the soil layer thickness, groundwater level, and the mean value / variance value of the static and dynamic parameters of the soil. The compaction effect of the gravel piles during the stone pile construction process will affect the static and dynamic parameters of the dam foundation soil. The high overburden stress generated during the dam construction process and the water storage during the service period of the dam body will increase the ground stress and also affect the static and dynamic parameters of the dam foundation soil. This influence law is studied through numerical simulation or centrifuge shaking table model test, considering the influence of gravel pile construction, dam construction and water storage. Based on the mean and variance distribution maps of the static and dynamic parameters of the natural dam foundation soil established in the above steps, the mean and variance distribution maps of the static and dynamic parameters of the dam foundation soil in each period of the dam foundation gravel pile construction, dam construction and water storage during the service period of the dam body are established respectively;

[0066] Step S2.3, construct a natural dam foundation-bedrock model, use gravel piles, overburden stress and water level to simulate the external environment of the dam foundation-bedrock model under different working conditions, so as to obtain the dam foundation-bedrock model under different working conditions; then, perform numerical simulation or centrifuge vibration table model test on the dam foundation-bedrock model under different working conditions, and combine the soil parameter distribution map of each soil layer in the natural site obtained in step S2.2 to obtain the spatial distribution map of soil parameters of each soil layer in the site under different working conditions.

[0067] In step S3, the simplified calculation model of liquefaction damage is expressed as follows:

[0068]

[0069]

[0070]

[0071]

[0072] Among them, P l represents the probability of earthquake liquefaction of the soil layer; FS represents the safety factor against liquefaction of the soil layer; CRR represents the cyclic stress ratio of the soil layer, and CSR represents the cyclic resistance ratio of the soil layer; a max is the horizontal peak acceleration of the dam base; g is the gravitational acceleration; σ vc is the total vertical stress on the soil layer; σ vc ' is the overlying effective stress; γ d V is the stress stiffness reduction factor of the soil layer; s1 is the shear wave velocity corrected for overburden stress; V s1 ' is the upper limit shear wave velocity of soil liquefaction. When the average clay content FC≤5%, V s1 'Take 215m / s, when FC≥35%, V s1'Take 200m / s; when 5%<FC<35%, V s1 'It can be calculated by linear interpolation; MSF represents the magnitude scale factor.

[0073] In the simplified calculation model of liquefaction damage, the stress stiffness reduction factor γ of the soil layer is d According to the following formula:

[0074]

[0075] Where z represents the average depth of the soil layer;

[0076] Shear wave velocity V after overburden stress correction s1 The expressions of the magnitude scale factor MSF are as follows:

[0077]

[0078]

[0079] Where V s is the shear wave velocity; P a is atmospheric pressure; M w is the moment magnitude.

[0080] Step S4 is as follows: first, the dam foundation seismic parameter hazard curve in step S1 and the soil parameter spatial distribution map obtained in step S2 are input into the geographic information analysis software GIS, and the simplified calculation model of liquefaction damage in step S3 is selected in the geographic information analysis software GIS. The simplified calculation model of liquefaction damage is based on the input horizontal peak acceleration of the dam foundation, the soil layer thickness d, and the groundwater level z. w , and soil static and dynamic parameter processing combined with Monte Carlo simulation to obtain the seismic liquefaction probability P of the soil layer l , and according to the mean and variance of the seismic liquefaction probability of each soil layer at all locations on the site under different working conditions, the mean distribution diagram and variance distribution diagram of the seismic liquefaction probability under different working conditions are drawn respectively, such as Figure 2 As shown, Figure 2 The left figure shows the mean distribution of liquefaction probability. Figure 2 The right figure is the liquefaction probability variance distribution diagram, where the soil density is used to calculate the vertical total stress σ on the soil layer vc .

[0081] The working conditions of the dam foundation-bedrock model include the gravel pile construction period, the dam building period and the dam body service and water storage period. The dam foundation-bedrock model during the gravel pile construction period is simulated by applying gravel piles to the dam foundation in the natural dam foundation-bedrock model. The dam foundation-bedrock model during the dam building period is simulated by applying a given overburden stress on the dam foundation surface of the dam foundation-bedrock model during the gravel pile construction period. The dam foundation-bedrock model during the dam body service and water storage period is simulated by applying a given water level in the dam foundation-bedrock model during the dam building period.

[0082] The above description is only a specific implementation mode of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for assessing the risk of dam foundation liquefaction based on probability analysis, characterized in that: The following steps are involved: Step S1: First, based on the on-site earthquake safety assessment report, considering the compaction effect of gravel piles on the dam foundation and the effect of overburden stress on ground stress increase, establish the dam foundation surface seismic parameter hazard curve under different working conditions; Step S2: Next, draw a spatial distribution diagram of soil parameters of the dam foundation soil under different working conditions; Step S3, then selecting an appropriate simplified calculation model for liquefaction damage according to site conditions and centrifuge shaking table model tests; Step S4: Based on the dam foundation seismic parameter hazard curve in step S1 and the soil parameter spatial distribution map obtained in step S2, combined with the simplified calculation model of liquefaction seismic damage, Monte Carlo simulation is used in geographic information analysis software GIS to perform spatial analysis of dam foundation liquefaction seismic damage, and the mean distribution map and variance distribution map of the seismic liquefaction probability of each layer of soil in the site under different working conditions are obtained; Step S5: Finally, using the earthquake liquefaction probability P l The mean distribution diagram and variance distribution diagram of the soil are used to evaluate the seismic liquefaction risk of each layer of soil in the site under different working conditions.

2. The method for assessing the risk of dam foundation liquefaction based on probability analysis according to claim 1 is characterized by: The step S1 specifically includes the following steps: Step S1.1, according to the annual average exceedance probability of the bedrock horizontal peak acceleration in the earthquake safety assessment report, draw a bedrock seismic parameter hazard curve, wherein the ordinate of the bedrock seismic parameter hazard curve is the bedrock horizontal peak acceleration, and the abscissa is the annual average exceedance probability corresponding to the bedrock horizontal peak acceleration; Step S1.2, construct a dam foundation-bedrock model, use gravel piles, overburden stress and water level to simulate the external environment of the dam foundation-bedrock model under different working conditions, and obtain the dam foundation-bedrock model under different working conditions; then, perform numerical simulation or centrifuge vibration table model test on the dam foundation-bedrock model under different working conditions, and combine with the bedrock seismic motion parameter hazard curve to draw the dam foundation surface seismic motion parameter hazard curve under different working conditions, the ordinate of the dam foundation surface seismic motion parameter hazard curve is the horizontal peak acceleration of the dam foundation surface, and the abscissa is the annual average exceedance probability corresponding to the horizontal peak acceleration of the dam foundation surface.

3. The method for assessing the risk of dam foundation liquefaction based on probability analysis according to claim 1 is characterized by: The step S2 is specifically as follows: Step S2.1: First, obtain the location of each drilling point in the site, and then conduct geotechnical tests on the soil at each drilling point to obtain the soil layer thickness d and groundwater level z of each soil layer at each drilling point. w , and the mean and variance of soil static and dynamic parameters, wherein the soil static and dynamic parameters include soil density ρ and shear wave velocity V s , the mean value and variance of the static and dynamic parameters of the soil layer are obtained by respectively calculating the mean value and variance of the static and dynamic parameters of the soil at different depths in the same soil layer; Step S2.2: calculate the soil thickness d and groundwater level z of each soil layer at each drilling point. w The mean and variance of the static and dynamic parameters of the soil are imported into the geographic information analysis software GIS. The thickness of each soil layer d and the groundwater level z at all locations of the site are obtained using the geographic information analysis software GIS. w , and the mean and variance of soil static and dynamic parameters, and draw a spatial distribution map of soil parameters for each soil layer in a natural site, wherein the spatial distribution map of soil parameters includes a soil layer thickness distribution map, a groundwater level distribution map, a mean distribution map of soil static and dynamic parameters, and a variance distribution map of soil static and dynamic parameters; Step S2.3, construct a natural dam foundation-bedrock model, use gravel piles, overburden stress and water level to simulate the external environment of the dam foundation-bedrock model under different working conditions, so as to obtain the dam foundation-bedrock model under different working conditions; then, perform numerical simulation or centrifuge vibration table model test on the dam foundation-bedrock model under different working conditions, and combine the soil parameter distribution map of each soil layer in the natural site obtained in step S2.2 to obtain the spatial distribution map of soil parameters of each soil layer in the site under different working conditions.

4. The method for assessing the risk of dam foundation liquefaction based on probability analysis according to claim 1 is characterized by: In step S3, the simplified calculation model of liquefaction damage is expressed as follows: Among them, P l represents the probability of earthquake liquefaction of the soil layer; FS represents the safety factor against liquefaction of the soil layer; CRR represents the cyclic stress ratio of the soil layer, and CSR represents the cyclic resistance ratio of the soil layer; a max is the horizontal peak acceleration of the dam base; g is the gravitational acceleration; σ vc is the total vertical stress on the soil layer; σ vc ' is the overlying effective stress; γ d V is the stress stiffness reduction factor of the soil layer; s1 is the shear wave velocity corrected for overburden stress; V s1 ' is the upper limit shear wave velocity of soil liquefaction; MSF represents the magnitude scale factor.

5. The method for assessing the risk of dam foundation liquefaction based on probability analysis according to claim 1 is characterized by: The step S4 is specifically as follows: first, the dam foundation seismic parameter hazard curve in step S1 and the soil parameter spatial distribution map obtained in step S2 are input into the geographic information analysis software GIS, and the simplified calculation model of liquefaction seismic damage in step S3 is selected in the geographic information analysis software GIS. The simplified calculation model of liquefaction seismic damage is based on the input horizontal peak acceleration of the dam foundation, the soil layer thickness d, and the groundwater level z. w , and soil static and dynamic parameter processing to obtain the seismic liquefaction probability P of the soil layer l , and according to the mean and variance of the seismic liquefaction probability of each soil layer at all locations on the site, the mean distribution diagram and variance distribution diagram of the seismic liquefaction probability under different working conditions are drawn respectively.

6. The method for assessing the risk of dam foundation liquefaction based on probability analysis according to claim 2 is characterized by: The working conditions of the dam foundation-bedrock model include the gravel pile construction period, the dam building period and the dam body service and water storage period. The dam foundation-bedrock model during the gravel pile construction period is simulated by applying gravel piles to the dam foundation in the natural dam foundation-bedrock model. The dam foundation-bedrock model during the dam building period is simulated by applying overlying stress on the dam foundation surface of the dam foundation-bedrock model during the gravel pile construction period. The dam foundation-bedrock model during the dam body service and water storage period is simulated by applying a given water level to the dam foundation-bedrock model during the dam building period.

7. The method for assessing the risk of dam foundation liquefaction based on probability analysis according to claim 4 is characterized by: In the simplified calculation model of liquefaction damage, the stress stiffness reduction factor γ of the soil layer is d According to the following formula: Where z represents the average depth of the soil layer; Shear wave velocity V after overburden stress correction s1 The expressions of the magnitude scale factor MSF are as follows: Where V s is the shear wave velocity; P a is atmospheric pressure; M w is the moment magnitude.

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