A Time-Varying Seismic Toughness Analysis Method for Shield Tunnels Considering Chloride Ion Erosion

Abstract

The present invention provides a method for analyzing the time-varying seismic toughness of a shield tunnel considering chloride ion corrosion, comprising the following steps: determining soil conditions and tunnel physical and mechanical parameters based on actual projects, and rationally selecting a plurality of seismic motion records; determining a performance degradation model of steel and concrete materials under the influence of chloride ion corrosion; establishing a finite element dynamic analysis model of a soil-tunnel system under different corrosion conditions and calculating its dynamic response; using relative bending moment ratio and peak acceleration as tunnel structural performance parameters and seismic intensity parameters for vulnerability analysis; establishing a seismic probability demand model for the tunnel under different corrosion conditions and obtaining key parameters of a vulnerability curve; establishing a time-varying seismic vulnerability curve for the tunnel under different corrosion conditions based on the obtained key parameters; establishing a tunnel function recovery curve under different service times; and performing a time-varying seismic toughness analysis of the tunnel based on the obtained vulnerability curve and the obtained function curve.

Description

Technical Field

[0001] This invention relates to the field of seismic risk assessment of tunnel structures, and in particular to a method for analyzing the time-varying seismic toughness of shield tunnels that takes chloride ion erosion into account. Background Technology

[0002] Rail transit plays a vital role in urbanization, not only enhancing urban productivity and promoting economic prosperity but also significantly improving urban traffic efficiency and alleviating congestion. Tunnels, as an indispensable part of rail transit construction, play a crucial role. The impact of earthquakes is a critical factor that cannot be ignored during tunnel design. Major earthquakes can cause severe damage to tunnels, especially when the tunnel lining's performance deteriorates due to years of chloride ion corrosion, increasing the likelihood of collapse and severely impacting disaster relief and urban recovery. While there are numerous studies on tunnel seismic toughness analysis, the time-varying seismic toughness variation law of shield tunnels considering chloride ion corrosion remains unclear, making it difficult to assess the seismic toughness of tunnels under different service durations. Therefore, research on the time-varying seismic toughness of tunnels considering chloride ion corrosion remains of significant value and importance.

[0003] The concept of "resilience" refers to a system's ability to maintain and restore its original function when subjected to changes and disturbances. The seismic toughness of tunnel structures reflects their ability to maintain certain performance and restore their original function after an earthquake. Analyzing the seismic toughness of tunnel structures can enrich tunnel seismic resistance theory and provide guidance for risk assessment and post-earthquake rescue. Currently, many scholars have conducted research on tunnel seismic toughness, established various toughness assessment methods, considered multiple toughness evaluation indicators such as tunnel convergence deformation and settlement, and revealed the influence of different service conditions on tunnel seismic toughness.

[0004] Compared to above-ground structures, tunnels are subject to more uncertainties and complex conditions during operation, with chloride ion corrosion being particularly significant. Chloride ion corrosion can lead to problems such as steel reinforcement corrosion and water leakage in the lining. Therefore, many shield tunnel structures will be in service in the future, becoming indispensable infrastructure and lifeline projects in cities. These tunnels must not only withstand the severe challenges posed by earthquakes but also bear the significant risks from the deterioration of lining materials. Therefore, studying the impact of chloride ion corrosion on tunnels has important engineering significance and practical value.

[0005] Chloride ion corrosion has a profound impact on the long-term service performance of tunnels, causing not only disasters such as lining leakage but also gradually weakening the tunnel's seismic resistance. Therefore, studying the influence of chloride ion corrosion on the seismic toughness of tunnel structures is of great value. However, current research on tunnel seismic toughness has not fully considered this factor, and the time-varying seismic toughness variation law of tunnels under the influence of chloride ion corrosion remains unclear and requires further analysis. Therefore, proposing a time-varying seismic toughness analysis method for shield tunnels that considers chloride ion corrosion has important guiding significance for tunnel design, operation, and maintenance. Summary of the Invention

[0006] The purpose of this invention is to address the problem of chloride ion erosion affecting the seismic performance of tunnels by providing a time-varying seismic toughness analysis method for tunnels that considers chloride ion erosion. This method is based on nonlinear incremental dynamic analysis and establishes a finite element numerical model of the soil-tunnel system considering the influence of chloride ion erosion, enabling the analysis of the seismic toughness of tunnels under different degrees of chloride ion erosion.

[0007] Technical solution of the present invention:

[0008] A time-varying seismic toughness analysis method for shield tunnels considering chloride ion erosion includes the following steps:

[0009] (1) Determine the soil conditions and tunnel physical and mechanical parameters based on the actual project, and select ground motion records according to the specifications;

[0010] (2) Determine the initial corrosion time of the steel bars and the performance degradation model of steel bars and concrete materials under the influence of chloride ion corrosion;

[0011] (3) Based on steps (1) and (2), establish a finite element dynamic analysis model of the soil-tunnel system under different erosion conditions and calculate its dynamic response;

[0012] (4) The relative bending moment ratio and peak ground acceleration are used as tunnel structure performance parameters and seismic intensity parameters for vulnerability analysis;

[0013] (5) Based on the results of step (3) and combined with step (4), establish a seismic probability demand model for the tunnel under different erosion conditions and obtain the key parameters of the vulnerability curve;

[0014] (6) Based on the key parameters obtained in step (5), establish time-varying seismic vulnerability curves of tunnels under different erosion conditions;

[0015] (7) Establish tunnel function recovery curves under different service times;

[0016] (8) Based on the vulnerability curve obtained in step (6) and the functional recovery curve obtained in step (7), the time-varying seismic toughness analysis of the tunnel is performed.

[0017] Based on nonlinear incremental dynamic analysis of tunnels, this invention proposes a time-varying seismic toughness analysis method for tunnels that can fully consider chloride ion erosion. This method can quantitatively evaluate the seismic vulnerability and seismic toughness of tunnels under different erosion conditions and earthquake intensities.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] Previous methods for analyzing the seismic toughness of tunnels have considered many influencing factors, but rarely the impact of chloride ion erosion. Therefore, to analyze the seismic performance of tunnels under different erosion states, a time-varying seismic toughness analysis method considering chloride ion erosion is needed. This method fully considers the impact of chloride ion erosion on the deterioration of steel reinforcement and concrete cover performance. A dynamic analysis model is established using a finite element platform, and the seismic response of the tunnel is obtained through analysis and calculation. This allows for the plotting of the tunnel's time-varying vulnerability curve and further the determination of its time-varying seismic toughness. This method has certain reference value for assessing the seismic toughness of tunnels under chloride ion erosion. Attached Figure Description

[0020] Figure 1 Flowchart of the time-varying seismic toughness analysis method for shield tunnels considering chloride ion erosion in this invention;

[0021] Figure 2 A probability requirement model for tunnel seismic resistance under the influence of chloride ion erosion;

[0022] Figure 3 A time-varying seismic vulnerability curve for tunnels that takes chloride ion erosion into account;

[0023] Figure 4 A time-varying seismic toughness curve of a tunnel considering chloride ion erosion.

[0024] The present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments.

[0025] Implementation Case:

[0026] like Figure 1 As shown, a time-varying seismic toughness analysis method for shield tunnels considering chloride ion erosion includes the following steps:

[0027] (1) Determine the soil conditions and tunnel physical and mechanical parameters based on the actual project, and select ground motion records according to the specifications;

[0028] (2) Determine the initial corrosion time of the steel bars and the performance degradation model of steel bars and concrete materials under the influence of chloride ion corrosion;

[0029] (3) Based on steps (1) and (2), establish a finite element dynamic analysis model of the soil-tunnel system under different erosion conditions and calculate its dynamic response;

[0030] (4) The relative bending moment ratio and peak ground acceleration are used as tunnel structure performance parameters and seismic intensity parameters for vulnerability analysis;

[0031] (5) Based on the results of step (3) and combined with step (4), establish a seismic probability demand model for the tunnel under different erosion conditions and obtain the key parameters of the vulnerability curve;

[0032] (6) Based on the key parameters obtained in step (5), establish time-varying seismic vulnerability curves of tunnels under different erosion conditions;

[0033] (7) Establish tunnel function recovery curves under different service times;

[0034] (8) Based on the vulnerability curve obtained in step (6) and the functional curve obtained in step (7), the time-varying seismic toughness analysis of the tunnel is performed.

[0035] The specific steps of each embodiment of the present invention are as follows:

[0036] (1) Determine the soil conditions and physical and mechanical parameters of the tunnel based on the actual project. At the same time, select several ground motion records with response spectra similar to those in the relevant regional codes based on the seismic response spectra.

[0037] The physical and mechanical parameters of the tunnel selected in this case study are as follows: shield tunnel depth of 30m, tunnel diameter of 6.2m, segment thickness of 0.35m, concrete grade of C50, steel reinforcement grade of HRB400, reinforcement ratio of 1.03%, and concrete cover thickness of 5cm. Typical soft soil parameters from Shanghai were selected for the soil conditions. Based on the seismic response spectrum of the Shanghai Building Seismic Design Code, 15 horizontal ground motion records were selected from the website of the Pacific Earthquake Research Center in the United States for analysis.

[0038] (2) Determine the initial corrosion time of the reinforcing steel. By selecting appropriate time-varying models for steel reinforcement parameters and concrete materials that consider chloride ion corrosion, the formula for calculating the average corrosion depth of steel reinforcement used here is as follows:

[0039]

[0040] Where T represents the service time. The following table shows the concrete strength of the protective layer considering chloride ion corrosion rate:

[0041]

[0042] in η For steel reinforcement corrosion rate, f c For concrete compressive strength, f t This refers to the tensile strength of concrete.

[0043] (3) Based on the physical and mechanical parameters of the soil and tunnel and the ground motion determined in step (1), the lining performance degradation model under the influence of initial rust time and chloride ion erosion determined in step (2), establish a finite element dynamic analysis model of the soil-tunnel system under different erosion conditions, and calculate its dynamic response.

[0044] (4) Calculate the relative bending moment ratio using the dynamic analysis results of the finite element model, and use it as the structural performance parameter of the tunnel. DI Simultaneously, different failure states corresponding to structural performance parameters are determined; peak ground acceleration is used. PGA As a parameter of seismic intensity IM The two selected parameters will be used in subsequent seismic vulnerability analysis. The formula for calculating the relative moment ratio of the structural performance parameter is as follows:

[0045]

[0046] in M The actual bending moment of the tunnel lining section is obtained through finite element model analysis and calculation. M R The bending moment bearing capacity of the lining section.

[0047] (5) Based on the structural performance parameters selected in step (4) DI and seismic intensity parameters IM Establish a seismic probability requirement model for tunnels under different erosion conditions (e.g.) Figure 2 Then, the key parameters of the fragility curve are calculated using the function obtained through linear regression: the parameters corresponding to each failure state. IM The median value and the logarithmic standard deviation of the seismic probability demand model.

[0048] (6) Based on the key parameters obtained in step (5), establish tunnel vulnerability curves under different chloride ion erosion conditions (e.g. Figure 3 The formula for the fragility curve is as follows:

[0049]

[0050] in When an earthquake is of a certain intensity IM When, exceeding a certain state of destruction d si The probability of; This represents the cumulative probability function of the standard normal density. The threshold values ​​for each damage state obtained in step (6) are the ground motion intensity indices. The total logarithmic standard deviation, which shows the variability of the curve, is obtained by the following formula.

[0051]

[0052] in , , These represent the uncertainties in the definition of damage state, the uncertainties in tunnel seismic response and bearing capacity, and the uncertainties in ground motion, respectively. and Value: , . The value is obtained from step (5).

[0053] (7) Based on the empirical functional recovery curves of tunnel structures under three damage conditions (minor, moderate, and severe) provided by the Federal Emergency Management Agency (FEMA), establish tunnel functional recovery curves Q for different service times. (t) The formula is as follows:

[0054]

[0055] in This represents the function of the tunnel at time t and damage state i. For tunnels under earthquake intensity IM In the case of The probability of a destroyed state.

[0056] (8) Based on the time-varying vulnerability curves of the tunnel under different erosion conditions obtained in step (6), and the tunnel functional recovery curve obtained in step (7). Q (t) Quantitatively assess the seismic toughness of tunnels Re The seismic toughness curve of the tunnel is obtained (e.g.) Figure 4 The formula for calculating the toughness curve is as follows:

[0057]

[0058] in The event that occurs during an earthquake. This refers to the time required for the tunnel to fully recover its functionality.

[0059] pass Figure 4The time-varying toughness curve of the tunnel can be used to analyze the seismic toughness of the tunnel under the influence of surface overload. The results show that when no earthquake occurs, the seismic toughness Re value of the tunnel is equal to 1. As the intensity of the earthquake increases, the Re value gradually decreases. Under the same PGA conditions, the longer the service time, the lower the seismic toughness Re value of the tunnel. For example, when the PGA is 1.0g, the seismic toughness index of the tunnel with a service time of 0 years is 0.939, while the corresponding Re values ​​for service times of 25 years, 50 years, 75 years, and 100 years are 0.909, 0.852, 0.797, and 0.748, respectively, which are 3.2%, 9.3%, 15.1%, and 20.3% lower than that with a service time of 0 years. Through this case, it can be concluded that the method of the present invention can obtain the seismic toughness index of the tunnel under different chloride ion erosion conditions and quantitatively analyze its time-varying law, so as to reasonably assess the seismic risk of the tunnel. This method is particularly suitable for earthquake-prone areas, as it can fully consider the impact of the service life of shield tunnels and provide important guidance for the time-varying seismic toughness analysis of tunnels, disaster relief, and tunnel function restoration.

Claims

1. A method for analyzing the time-varying seismic toughness of shield tunnels considering chloride ion erosion, characterized in that, The steps include the following: (1) Determine the soil conditions and tunnel physical and mechanical parameters based on the actual project, and select ground motion records according to the specifications; (2) Determine the initial corrosion time of the steel bars and the performance degradation model of steel bars and concrete materials under the influence of chloride ion corrosion; (3) Based on steps (1) and (2), establish a finite element dynamic analysis model of the soil-tunnel system under different erosion conditions and calculate its dynamic response; (4) The relative bending moment ratio and peak ground acceleration are used as tunnel structure performance parameters and seismic intensity parameters for vulnerability analysis; (5) Based on the results of step (3) and combined with step (4), establish a seismic probability demand model for the tunnel under different erosion conditions and obtain the key parameters of the vulnerability curve; (6) Based on the key parameters obtained in step (5), establish time-varying seismic vulnerability curves of tunnels under different erosion conditions; (7) Establish tunnel function recovery curves under different service times; (8) Based on the vulnerability curve obtained in step (6) and the functional recovery curve obtained in step (7), the time-varying seismic toughness analysis of the tunnel is performed.

2. The method for analyzing the time-varying seismic toughness of shield tunnels considering chloride ion erosion as described in claim 1, characterized in that, In step (3): Based on the soil conditions, tunnel physical and mechanical parameters and seismic waves determined in step (1), the finite element dynamic analysis model of the soil-tunnel system under different chloride ion erosion conditions is established by using the initial rusting time of the lining and the deterioration model of the performance of steel bars and protective concrete under the influence of chloride ion erosion determined in step (2), and its dynamic response is calculated.

3. The method for analyzing the time-varying seismic toughness of shield tunnels considering chloride ion erosion as described in claim 1, characterized in that, In step (4): The relative bending moment ratio, i.e., the ratio of the lining bending moment to the bending moment bearing capacity, is used as a structural performance parameter of the tunnel. DI At the same time, determine the failure state corresponding to the structural performance parameters; Peak ground acceleration PGA As a parameter of seismic intensity IM The two parameters selected above are used for subsequent seismic vulnerability analysis; The formula for calculating the relative moment ratio of structural performance parameters is as follows: in M The actual bending moment of the tunnel lining section is obtained through finite element model analysis and calculation. M R The bending moment bearing capacity of the lining section.

4. The method for analyzing the time-varying seismic toughness of shield tunnels considering chloride ion erosion as described in claim 1, characterized in that, In step (5): Based on the structural performance parameters selected in step (4) DI and seismic intensity parameters IM Establish a seismic probability requirement model for tunnels under different erosion conditions, that is, in IM-DI Plot all the calculation results of step (3) on the coordinate system and perform linear regression. Then, calculate the key parameters of the fragility curve using the function obtained from the linear regression: the parameters corresponding to each failure state. IM The median value and the logarithmic standard deviation of the seismic probability demand model β D ; The seismic resistance probability requirement model is as follows: Where a and b are parameters obtained from regression analysis.

5. The method for analyzing the time-varying seismic toughness of shield tunnels considering chloride ion erosion as described in claim 1, characterized in that, In step (6): Based on the median and logarithmic standard deviation obtained in step (5), a time-varying vulnerability analysis model for tunnels is established, namely, the time-varying vulnerability curves of tunnels under different erosion conditions, and the formula is as follows: in When an earthquake is of a certain intensity IM When, exceeding a certain state of destruction d si The probability of; This represents the cumulative probability function of the standard normal density. The threshold values ​​for each damage state obtained in step (6) are the ground motion intensity indices. The total logarithmic standard deviation, which shows the variability of the curve, is obtained by the following formula; in , , These represent the uncertainties in the definition of damage state, the uncertainties in tunnel seismic response and bearing capacity, and the uncertainties in ground motion, respectively. and Value: , , The value is obtained from step (5).

6. The method for analyzing the time-varying seismic toughness of shield tunnels considering chloride ion erosion as described in claim 1, characterized in that, In step (7): Based on the empirical functional recovery curves of tunnel structures under three damage conditions (minor, moderate, and severe) provided by the Federal Emergency Management Agency (FEMA), a tunnel functional recovery curve Q is established for different service times. (t) The formula is as follows: in This represents the function of the tunnel at time t and damage state i. For tunnels under earthquake intensity IM In the case of The probability of a destroyed state.

7. The method for analyzing the time-varying seismic toughness of shield tunnels considering chloride ion erosion as described in claim 1, characterized in that, In step (8): Based on the tunnel time-varying vulnerability curves under different erosion conditions obtained in step (6), and the tunnel function recovery curves obtained in step (7), Q (t) Quantitatively assess the seismic toughness of tunnels Re , which is calculated as follows: in The time when the earthquake occurred. The time required for the tunnel to fully recover its functionality; for t The structural performance at time t is calculated using the following formula: in Indicates the tunnel is in t Time and i Function in the damaged state For tunnels under earthquake intensity IM In the case of The probability of a destroyed state.

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