Shield tunnel earthquake vulnerability analysis method considering surface overload influence

Abstract

The invention relates to a shield tunnel earthquake vulnerability analysis method considering the influence of surface overload. The method comprises the following steps: determining the mechanical properties of a tunnel material and the physical and mechanical parameters of a soil layer; ground surface overload cases are investigated, and ground surface overload working conditions are determined; selecting seismic waves and carrying out one-dimensional field equivalent linear analysis on soil conditions; establishing a soil body-tunnel dynamic finite element numerical model considering earth surface overload; determining a seismic oscillation intensity index, a tunnel damage index and a damage state; and establishing a tunnel anti-seismic probability demand model under the influence of different surface overloads. And establishing a tunnel structure earthquake vulnerability curve under the influence of surface overload based on the key parameters. According to the method, based on a nonlinear incremental dynamic analysis method, a soil body-tunnel system finite element numerical model considering the surface overload influence is established, and the tunnel earthquake vulnerability and anti-seismic performance under different surface overload influences can be quantitatively evaluated.

Description

Technical Field

[0001] The invention relates to the field of tunnel structure seismic risk assessment, in particular to a shield tunnel seismic vulnerability analysis method taking into account the influence of surface overload. Background Art

[0002] With the development of urban civilization and the increasing saturation of space resource utilization, the number of underground structures in my country has gradually increased, and their uses have become increasingly extensive. They play an important role in the fields of transportation systems, municipal water and electricity, resource mining, and national defense projects. Tunnels used for transportation are one of the most important parts. Earthquake disasters and excessive surface overloads can cause serious damage to them, which will cause huge losses to the city and even affect the lives of citizens.

[0003] Seismic vulnerability expresses the probability of a structure exceeding a certain damage state under different earthquake intensities. It can quantitatively analyze the seismic performance of the structure and provide an important reference for the seismic design of urban construction. Many scholars have established different research methods for the seismic vulnerability analysis of tunnel structures, mainly including: (1) vulnerability analysis based on expert judgment; (2) vulnerability analysis based on historical earthquake damage surveys; (3) vulnerability analysis based on numerical methods; (4) vulnerability analysis based on experimental data. In the early days when science and technology and numerical analysis software were not yet developed, vulnerability analysis based on expert judgment and historical earthquake damage surveys was mainly used. Although these two methods can quickly make preliminary judgments, they are relatively subjective and cannot be applied to all geographical areas. They can no longer meet the current vulnerability analysis requirements. With the development of science and technology, scholars have begun to use methods such as numerical analysis to conduct detailed vulnerability analysis, which can perform accurate vulnerability analysis based on a large amount of data and has been used and improved by many scholars.

[0004] Tunnel damage caused by surface overload is a common situation in urban development. Since the development of subway lines is often forward-looking and plays a role in leading the development of urban economy, there are often many commercial developments along the subway lines, which means that surface overload caused by construction may occur above the subway. It can be seen that analyzing the impact of surface overload on tunnels has important practical value for urban development. At present, the main research methods for the impact of surface overload on tunnels are: field measurement method, model test method, numerical analysis method, and theoretical analysis method. Among them, the field measurement method has better effect, but it is more expensive and time-consuming. Although the model test method is difficult to reproduce complex working conditions, it takes less time and can calculate more working conditions. It is a method commonly used by scholars.

[0005] In addition to the horizontal shear deformation transmitted by the surrounding soil layers, the tunnel structure is also affected by vertical loads such as surface overload under earthquake action, which will increase the risk of seismic damage to the overall structure. It can be seen that the surface overload condition has an important influence on the seismic performance of the tunnel structure, but this factor has not been given enough attention in current related studies. The relationship between the surface overload and the seismic performance of the tunnel structure is not clear enough, and it is necessary to further analyze the change law of the seismic vulnerability of the tunnel structure under the influence of surface overload. Therefore, a method for analyzing the seismic vulnerability of the tunnel under the influence of different surface overloads is proposed, which can provide suggestions and guidance for the seismic optimization design and reinforcement scheme of the tunnel structure, which has important theoretical significance and engineering practical value. Summary of the invention

[0006] The purpose of this application is to provide a tunnel seismic vulnerability analysis method for the combined effects of surface overload and earthquake that may occur in actual construction. This method is based on the nonlinear incremental dynamic analysis method and establishes a finite element numerical model of the soil-tunnel system that takes into account the influence of surface overload. It can quantitatively evaluate the seismic vulnerability and seismic performance of the tunnel under the influence of different surface overloads.

[0007] The technical solutions provided by this application are as follows:

[0008] A shield tunnel seismic vulnerability analysis method considering the influence of surface overload comprises the following steps:

[0009] S1. Determine the mechanical properties of tunnel materials and the physical and mechanical parameters of soil layers;

[0010] S2. Investigate cases where tunnels are affected by surface overloads to determine the reasonable location, size and scope of surface overloads;

[0011] S3, selecting a suitable seismic wave and performing a one-dimensional field equivalent linear analysis on the soil conditions obtained in step S1 to obtain the elastic modulus and Rayleigh damping parameters of the soil;

[0012] S4. Based on the physical and mechanical parameters of the tunnel and soil layer determined in steps S1, S2 and S3, as well as the seismic wave and surface overload conditions, a soil-tunnel dynamic finite element numerical model considering the surface overload is established, working conditions with different combinations of surface overload and seismic intensity are designed, and the dynamic response of the soil-tunnel system is obtained through a large number of numerical calculations;

[0013] S5, selecting the maximum peak acceleration of the input seismic wave as the seismic intensity index IM; selecting the diameter deformation rate of the tunnel as the damage index DM; determining the damage state of the tunnel and the damage index threshold corresponding to each damage state;

[0014] S6. Based on the seismic intensity index IM and the damage index DM selected in step S5, a tunnel seismic probability demand model under different surface overloads is established, as shown in Formula 3:

[0015] lnDM=alnIM+b, formula three

[0016] a and b are obtained through regression analysis; after obtaining the probability demand model, the key parameters for drawing the fragility curve are calculated: the median and logarithmic standard deviation β of the IM value corresponding to each damage state D ;

[0017] S7. Based on the key parameters, the seismic vulnerability curve of the tunnel structure under the influence of surface overload is established, as shown in Formula 5:

[0018]

[0019] Where P f When the earthquake reaches a certain intensity IM, it exceeds a certain damage state d si The probability of; φ represents the standard normal density cumulative probability function; S mi β is the earthquake intensity index threshold corresponding to each damage state obtained in step S6; tot is the overall logarithmic standard deviation.

[0020] In S1, the mechanical property parameters of tunnel materials include tunnel burial depth, tunnel diameter, lining thickness, and material parameters of concrete and steel bars; the physical and mechanical parameters of soil layers include soil layer thickness, soil layer density, cohesion, internal friction angle, Poisson's ratio, and shear wave velocity.

[0021] In S2, factors to be considered in determining the location of the surface overload include: whether the center of the surface overload deviates from the center of the tunnel, the size of the deviation distance, and the type and range of the load.

[0022] In S3, a one-dimensional site equivalent linear analysis is performed on the soil, a soil layer numerical model is established through software, the selected seismic wave is input to calculate the shear modulus of the soil layer, and then the elastic modulus E of the soil is obtained through formula 1; the characteristic period of the soil layer is determined, and the Rayleigh damping parameter of the soil layer is further obtained through calculation;

[0023]

[0024] Where G is the shear modulus and μ is the Poisson's ratio of the soil layer.

[0025] In S5, the tunnel diameter deformation rate is calculated as shown in Formula 2:

[0026]

[0027] The diameter of the tunnel before the earthquake is D, D1, and the diameter of the tunnel after being affected by surface overload and earthquake is D2, and ΔD is the change in diameter.

[0028] In S6, the logarithmic standard deviation β D Calculated by formula 4:

[0029]

[0030] Where n is the number of numerical model calculation results.

[0031] In S7, the total logarithmic standard deviation β tot From formula 6, we can get:

[0032]

[0033] where β ds , β C , β D They represent the uncertainty in the definition of the damage state, the uncertainty in the seismic response and bearing capacity of the tunnel, and the uncertainty in the ground motion.

[0034] The beneficial effects of the present invention are:

[0035] In the past, tunnel seismic vulnerability analysis considered the influence of the tunnel's own burial depth, diameter, material properties, and soil properties, but often did not consider the impact of external factors such as surface overload on the seismic performance of the tunnel. Therefore, in order to quantitatively analyze the impact of surface overload on the seismic performance of the tunnel, it is very important to adopt a tunnel seismic vulnerability analysis method that considers the impact of surface overload. This method fully considers the impact of changes in the location, size, and range of surface overload on the seismic performance of the tunnel, establishes a two-dimensional finite element model and conducts a large number of numerical simulations, draws seismic vulnerability curves under the influence of different surface overload conditions, and quantitatively analyzes the seismic vulnerability of the tunnel. This method has a certain reference value for the seismic risk assessment of tunnel structures under the influence of surface overload. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a flow chart of the tunnel seismic vulnerability analysis method considering the influence of surface overload according to the present invention.

[0037] Figure 2 Schematic diagram of the tunnel location, dimensions and load location for the implementation case.

[0038] Figure 3 Schematic diagram of the seismic probabilistic demand model under the influence of surface overload for the implementation case.

[0039] Figure 4 The seismic vulnerability curve of the tunnel under the influence of surface overload for the implementation case. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] like Figure 1 A shield tunnel seismic vulnerability analysis method considering the influence of surface overload is shown, comprising the following steps:

[0042] S1. Determine the mechanical properties of tunnel materials and the physical and mechanical parameters of soil layers.

[0043] The tunnel in this case is buried 10m deep, with a cross-sectional diameter of 6.2m and a reinforced concrete lining thickness of 0.35m. The tunnel structure is located as follows Figure 2 The material parameters are shown in Table 1:

[0044] Table 1 Material parameters of the tunnel

[0045]

[0046] S2. Investigate surface overload cases and determine appropriate surface overload conditions.

[0047] Investigate the cases of tunnels in the region affected by surface overload to determine the actual surface overload location, distance from the tunnel, size, range, and whether it is a uniformly distributed load, to provide reference for subsequent numerical simulation. The surface overload range selected in this case is 30m, located directly above the tunnel, and the overload conditions are 0kPa, 25kPa, 50kPa, 75kPa and 100kPa.

[0048] S3. Select appropriate seismic waves and perform one-dimensional linear analysis on the soil to supplement the characteristic parameters of the soil.

[0049] Consult the seismic design code of the area to be analyzed, and select a dozen suitable seismic waves that are close to the influence coefficient curve of the seismic design code for numerical simulation. Use one-dimensional linear analysis software to perform one-dimensional field equivalent linear analysis on the soil to obtain the equivalent shear modulus of each soil layer, and then use formula 1 to obtain the elastic modulus E of each soil layer:

[0050]

[0051] Where G is the shear modulus and μ is the Poisson's ratio of the soil layer. After obtaining the elastic modulus, it is necessary to determine the characteristic period of the soil layer, and then further obtain the Rayleigh damping parameter of the soil layer through calculation.

[0052] S4. Establish a finite element model of the soil-tunnel system under the influence of surface overload and perform a large number of calculations.

[0053] Based on the tunnel size and material information of this case, a soil-tunnel dynamic finite element numerical model is established. At the same time, a surface overload is applied to the soil surface of the model, and the seismic motion selected in step S3 is applied to the bottom of the model. The input seismic motion needs to be modulated to ensure that earthquakes of various intensities are reflected. After the model is established, a large number of numerical calculations are performed to obtain the dynamic response of the soil-tunnel system, and the most important thing is to obtain the rate of change of the tunnel diameter.

[0054] S5. Determine the earthquake intensity index (IM), tunnel damage index (DM) and damage state (DS).

[0055] The seismic intensity index (IM) selected in this case is the maximum peak acceleration of the input seismic wave, the tunnel damage index (DM) is the diameter deformation rate of the tunnel, and the damage state (DS) and the corresponding damage index range are shown in Table 2.

[0056] Table 2 Tunnel damage index

[0057]

[0058] The calculation of tunnel diameter deformation rate is shown in Formula 2:

[0059]

[0060] The diameter of the tunnel before the earthquake is D, D1, and the diameter of the tunnel after being affected by surface overload and earthquake is D2, and ΔD is the change in diameter.

[0061] S6. Establish a probability demand model for seismic resistance of tunnels under different surface overloads and obtain the key parameters of the fragility curve.

[0062] Collect and count the calculation results of the finite element model in step S4, and draw a fitting straight line graph with lnIM as the independent variable and lnDM as the dependent variable (such as Figure 3 ), and thus the seismic probability demand model is obtained as shown in Formula 3:

[0063] lnDM=alnIM+b, formula three

[0064] Where a and b are linear regression parameters. After drawing the probability demand model, the key parameters for drawing the fragility curve are calculated: the IM value corresponding to each damage state (such as Figure 3 As shown in the figure, that is, the horizontal coordinate value corresponding to the intersection of the fitting straight line and the damage index threshold) and the logarithmic standard deviation β D , the logarithmic standard deviation is calculated by formula 4.

[0065]

[0066] Where n is the number of numerical model calculation results.

[0067] S7. Establish the seismic vulnerability curve of the tunnel structure under the influence of surface overload based on key parameters.

[0068] The tunnel vulnerability curve under different surface overloads is established through the two key parameters in the previous step, such as Figure 4 , the vulnerability curve is shown in Formula 5.

[0069]

[0070] Where P f When the earthquake reaches a certain intensity IM, it exceeds a certain damage state d si The probability of; φ represents the standard normal density cumulative probability function; S mi β is the earthquake intensity index threshold corresponding to each damage state obtained in step S6; tot is the total logarithmic standard deviation, showing the variability of the curve, and is obtained by Equation 6.

[0071]

[0072] where β ds , β C , β D They represent the uncertainty of the damage state definition, the uncertainty of the tunnel seismic response and bearing capacity, and the uncertainty of the ground motion. ds With β C Value:

[0073] β ds =0.4, β C =0.3. D The value of is obtained by step S6.

[0074] pass Figure 4The seismic vulnerability of tunnels under the influence of surface overload can be analyzed. The results show that in the area where the case is implemented, when the tunnel cover thickness is small, the seismic performance of the tunnel decreases rapidly with the increase of surface overload. When the seismic intensity index is about 0.2g, when the surface overload increases from 0kPa to 100kPa, the probability of mild damage increases by about 3.5 times, the probability of moderate damage increases by nearly 6 times, and the probability of severe damage increases by nearly 9 times. Through this case, it can be concluded that the tunnel vulnerability curve established by this method can quantify the strength and degree of change of the seismic performance of the tunnel under the influence of different surface overloads, and reasonably evaluate the seismic risk of the tunnel. This method is particularly suitable for areas with frequent earthquakes, and construction on the top of existing tunnels leads to surface overloads such as soil piling. It can provide important guidance and practical value for the seismic vulnerability analysis and seismic design and construction of urban tunnels.

[0075] It is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered as exemplary and non-restrictive in all respects.

Claims

1. A shield tunnel seismic vulnerability analysis method considering the influence of surface overload, characterized in that: The following steps are involved: S1. Determine the mechanical properties of tunnel materials and the physical and mechanical parameters of soil layers; S2. Investigate cases where tunnels are affected by surface overloads to determine the reasonable location, size and scope of surface overloads; S3, selecting a suitable seismic wave and performing a one-dimensional field equivalent linear analysis on the soil conditions obtained in step S1 to obtain the elastic modulus and Rayleigh damping parameters of the soil; S4. Based on the physical and mechanical parameters of the tunnel and soil layer determined in steps S1, S2 and S3, as well as the seismic wave and surface overload conditions, a soil-tunnel dynamic finite element numerical model considering the surface overload is established, working conditions with different combinations of surface overload and seismic intensity are designed, and the dynamic response of the soil-tunnel system is obtained through a large number of numerical calculations; S5, selecting the maximum peak acceleration of the input seismic wave as the seismic intensity index IM; selecting the diameter deformation rate of the tunnel as the damage index DM; determining the damage state of the tunnel and the damage index threshold corresponding to each damage state; S6. Based on the seismic intensity index IM and the damage index DM selected in step S5, a tunnel seismic probability demand model under different surface overloads is established, as shown in Formula 3: lnDM=alnIM+b, formula three Where a and b are obtained through regression analysis; After obtaining the probability demand model, the key parameters for drawing the fragility curve are calculated: the median and logarithmic standard deviation β of the IM value corresponding to each damage state D ; S7. Based on the key parameters, the seismic vulnerability curve of the tunnel structure under the influence of surface overload is established, as shown in Formula 5: Where P f When the earthquake reaches a certain intensity IM, it exceeds a certain damage state d si The probability of; φ represents the standard normal density cumulative probability function; S mi β is the earthquake intensity index threshold corresponding to each damage state obtained in step S6; tot is the overall logarithmic standard deviation.

2. The shield tunnel seismic vulnerability analysis method considering the influence of surface overload according to claim 1 is characterized in that: In S1, the mechanical property parameters of tunnel materials include tunnel burial depth, tunnel diameter, lining thickness, and material parameters of concrete and steel bars; the physical and mechanical parameters of soil layers include soil layer thickness, soil layer density, cohesion, internal friction angle, Poisson's ratio, and shear wave velocity.

3. The shield tunnel seismic vulnerability analysis method considering the influence of surface overload according to claim 1 is characterized in that: In S2, factors to be considered in determining the location of the surface overload include: whether the center of the surface overload deviates from the center of the tunnel, the size of the deviation distance, and the type and range of the load.

4. The shield tunnel seismic vulnerability analysis method considering the influence of surface overload according to claim 1 is characterized in that: In S3, a one-dimensional site equivalent linear analysis is performed on the soil, a soil layer numerical model is established through software, the selected seismic wave is input to calculate the shear modulus of the soil layer, and then the elastic modulus E of the soil is obtained through formula 1; the characteristic period of the soil layer is determined, and the Rayleigh damping parameter of the soil layer is further obtained through calculation; Where G is the shear modulus and μ is the Poisson's ratio of the soil layer.

5. The shield tunnel seismic vulnerability analysis method considering the influence of surface overload according to claim 1 is characterized in that: In S5, the tunnel diameter deformation rate is calculated as shown in Formula 2: The diameter of the tunnel before the earthquake is D, D1, and the diameter of the tunnel after being affected by surface overload and earthquake is D2, and ΔD is the change in diameter.

6. The shield tunnel seismic vulnerability analysis method considering the influence of surface overload according to claim 1 is characterized in that: In S6, the logarithmic standard deviation β D Calculated by formula 4: Where n is the number of numerical model calculation results.

7. The shield tunnel seismic vulnerability analysis method considering the influence of surface overload according to claim 1 is characterized in that: In S7, the total logarithmic standard deviation β tot From formula 6, we can get: where β ds , β C , β D They represent the uncertainty in the definition of the damage state, the uncertainty in the seismic response and bearing capacity of the tunnel, and the uncertainty in the ground motion.

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