Shield tunnel time-varying anti-seismic toughness analysis method considering chloride ion erosion

Abstract

The invention provides a shield tunnel time-varying anti-seismic toughness analysis method considering chloride ion erosion, which comprises the following steps: determining soil conditions and tunnel physical and mechanical parameters according to actual engineering, and reasonably selecting a plurality of seismic oscillation records; determining a performance degradation model of the steel bar material and the concrete material under the influence of chloride ion erosion; building finite element dynamic analysis models of the soil body-tunnel system under different erosion conditions and calculating dynamic responses of the finite element dynamic analysis models; the relative bending moment ratio and the peak acceleration serve as tunnel structure performance parameters and seismic oscillation intensity parameters to be used for vulnerability analysis; an anti-seismic probability demand model of the tunnel under different erosion conditions is established, and key parameters of a vulnerability curve are obtained; establishing a tunnel time-varying earthquake vulnerability curve under different erosion conditions based on the obtained key parameters; establishing tunnel function recovery curves under different service times; and performing tunnel time-varying anti-seismic toughness analysis based on the obtained vulnerability curve and the obtained function curve.

Description

Technical Field

[0001] The invention relates to the field of tunnel structure seismic risk assessment, and in particular to a shield tunnel time-varying seismic toughness analysis method taking chloride ion corrosion into consideration. Background Art

[0002] Rail transit plays an extremely important role in the process of urbanization. It not only improves urban productivity and promotes economic prosperity, but also significantly improves urban traffic efficiency and relieves traffic pressure. Tunnels, as an indispensable part of rail transit construction, play an important role. In the design process of tunnels, the impact of earthquake disasters is an important factor that cannot be ignored. Major earthquake disasters will cause serious damage to tunnels, especially when the tunnel lining performance deteriorates due to long-term chloride ion erosion, there will be a greater possibility of damage, which will seriously affect emergency rescue and the recovery of urban functions. At present, there are many related studies on the seismic toughness analysis of tunnels, but the law of change of the time-varying seismic toughness of shield tunnels considering chloride ion erosion is still unclear, and it is difficult to evaluate the seismic toughness of tunnels under different service times. Therefore, it is still of great value and significance to study the time-varying seismic toughness of tunnels considering chloride ion erosion.

[0003] The concept of "resilience" refers to the ability of a system to maintain and restore its original function when it is subject to changes and disturbances. The seismic toughness of a tunnel structure reflects the ability of a tunnel to maintain certain performance and restore its original function after suffering an earthquake disaster. The seismic toughness analysis of tunnel structures can enrich the seismic theory of tunnels and provide guidance for risk assessment and post-earthquake rescue. At present, many scholars have conducted research on the seismic toughness of tunnels, established a variety of toughness evaluation methods, considered a variety of toughness evaluation indicators such as tunnel convergence deformation and settlement, and revealed the influence of different service conditions on the seismic toughness of tunnels.

[0004] Compared with above-ground structures, tunnels will be affected by more uncertain factors and complex conditions during operation, among which the problem of chloride ion corrosion is particularly significant. Chloride ion corrosion will lead to problems such as steel corrosion and lining water leakage. Although my country has a short history of building underground tunnels, the problem of chloride ion corrosion cannot be ignored. There have been many cases of structural damage or performance degradation due to problems such as steel corrosion. In my country, the design service life of tunnel structures is generally stipulated to be 100 years. Therefore, there will be many shield tunnel structures in service in the future, and they will become indispensable infrastructure and lifeline projects in cities. These tunnels not only have to cope with the severe test brought by earthquake disasters, but also have to bear the major risks brought by the deterioration of lining materials. Therefore, studying the impact of chloride ion corrosion on tunnels has important engineering significance and practical value.

[0005] The corrosion of chloride ions has a profound impact on the long-term service performance of tunnels. It will not only cause disasters such as lining leakage, but will also gradually weaken the seismic performance of tunnels. It can be seen that the study of the influence of chloride ion corrosion on the seismic toughness of tunnel structures is of great value, but this factor has not been fully considered in the current research on tunnel seismic toughness. The law of change of tunnel time-varying seismic toughness under the influence of chloride ion corrosion is still unclear and needs further analysis. Therefore, a shield tunnel time-varying seismic toughness analysis method considering chloride ion corrosion is proposed, which has important guiding significance for the design and operation and maintenance of tunnels. Summary of the invention

[0006] The purpose of the present invention is to provide a tunnel time-varying seismic toughness analysis method considering chloride ion erosion in order to solve the problem that chloride ion erosion affects the seismic performance of tunnels. Based on the nonlinear incremental dynamic analysis method, the method establishes a soil-tunnel system finite element numerical model considering the influence of chloride ion erosion, and can analyze the seismic toughness of tunnels under different chloride ion erosion degrees.

[0007] Technical solution of the present invention: A method for analyzing time-varying seismic toughness of a shield tunnel considering chloride ion corrosion comprises the following steps: (1) Determine soil conditions and tunnel physical and mechanical parameters based on actual projects, and select seismic records according to specifications; (2) Determine the initial corrosion time of 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), a finite element dynamic analysis model of the soil-tunnel system under different erosion conditions is established and its dynamic response is calculated; (4) Using relative bending moment ratio and peak acceleration as tunnel structure performance parameters and ground motion intensity parameters for vulnerability analysis; (5) Based on the results of step (3) and combined with step (4), a seismic probability demand model of the tunnel under different erosion conditions is established to obtain the key parameters of the fragility curve; (6) Establishing the time-varying seismic vulnerability curves of the tunnel under different erosion conditions based on the key parameters obtained in step (5); (7) Establish tunnel function recovery curves under different service times; (8) Based on the fragility 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.

[0008] Based on the nonlinear incremental dynamic analysis of the tunnel, the present invention proposes a tunnel time-varying seismic toughness analysis method which can fully consider chloride ion corrosion, and can quantitatively evaluate the seismic vulnerability and seismic toughness of the tunnel under different corrosion conditions and earthquake intensities.

[0009] Compared with the prior art, the present invention has the following advantages: In the past, the analysis methods of tunnel seismic toughness have considered many influencing factors, but rarely the influence of chloride ion erosion. Therefore, in order to analyze the seismic performance of tunnels under different erosion states, it is necessary to adopt the tunnel time-varying seismic toughness analysis method considering chloride ion erosion. This method fully considers the influence of chloride ion erosion on the performance degradation of steel materials and concrete cover. The dynamic analysis model is established through the finite element platform and the seismic response of the tunnel is obtained by analysis and calculation, so as to draw the time-varying vulnerability curve of the tunnel and further obtain the time-varying seismic toughness of the tunnel. This method has a certain reference value for the evaluation of tunnel seismic toughness under chloride ion erosion. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 This is a flow chart of the time-varying seismic toughness analysis method of a shield tunnel considering chloride ion corrosion according to the present invention; Figure 2 It is a probability demand model for seismic resistance of tunnels under the influence of chloride ion corrosion; Figure 3 The time-varying seismic vulnerability curve of the tunnel considering chloride ion corrosion; Figure 4 This is the time-varying seismic toughness curve of the tunnel considering chloride ion corrosion.

[0011] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments.

[0012] Implementation Cases: like Figure 1 As shown, a time-varying seismic toughness analysis method for shield tunnels considering chloride ion erosion includes the following steps: (1) Determine soil conditions and tunnel physical and mechanical parameters based on actual projects, and select seismic records according to specifications; (2) Determine the initial corrosion time of 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), a finite element dynamic analysis model of the soil-tunnel system under different erosion conditions is established and its dynamic response is calculated; (4) Using relative bending moment ratio and peak acceleration as tunnel structure performance parameters and ground motion intensity parameters for vulnerability analysis; (5) Based on the results of step (3) and combined with step (4), a seismic probability demand model of the tunnel under different erosion conditions is established to obtain the key parameters of the fragility curve; (6) establishing a time-varying seismic vulnerability curve of the tunnel under different erosion conditions based on the key parameters obtained in step (5); (7) Establish tunnel function recovery curves under different service times; (8) Based on the fragility curve obtained in step (6) and the function curve obtained in step (7), the time-varying seismic toughness analysis of the tunnel is performed.

[0013] The implementation case of the present invention, each step is as follows: (1) Determine the soil conditions and physical and mechanical parameters of the tunnel based on the actual project. At the same time, select several earthquake records with response spectra similar to those in the code according to the earthquake response spectrum in the corresponding area.

[0014] The physical and mechanical parameters of the tunnel selected in this case are: the shield tunnel is buried 30m deep, the tunnel diameter is 6.2m, the segment thickness is 0.35m, the concrete grade is C50, the steel grade is HRB400, the reinforcement ratio is 1.03%, and the concrete cover thickness is 5cm. The soil conditions are the typical soft soil parameters of Shanghai. According to the seismic response spectrum of the Shanghai Building Seismic Design Code, 15 horizontal seismic motion records were selected from the website of the Pacific Earthquake Research Center in the United States for analysis.

[0015] (2) Determine the initial corrosion time of steel bars , select appropriate steel bar parameter time-varying model and concrete material time-varying model considering chloride ion corrosion. The calculation formula for the average steel bar corrosion depth used here is as follows: Where T is the service time, The corrosion rate and the strength of the protective layer concrete considering chloride ion erosion are shown in the following table: in η is the steel bar corrosion rate, f c is the compressive strength of concrete, f t is the tensile strength of concrete.

[0016] (3) Based on the physical and mechanical parameters of the soil and tunnel and the seismic motion determined in step (1), the initial rust time of the lining and the lining performance degradation model under the influence of chloride ion corrosion determined in step (2), a finite element dynamic analysis model of the soil-tunnel system under different corrosion conditions is established, and its dynamic response is calculated.

[0017] (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 , and determine the different damage states corresponding to the structural performance parameters; using the peak acceleration of the surface PGA As a parameter of ground motion intensity IM The two selected parameters will be used in the subsequent seismic vulnerability analysis. The calculation formula of the structural performance parameter relative moment ratio is as follows: in M is the actual bending moment of the tunnel lining section, obtained through finite element model analysis and calculation. M R is the moment bearing capacity of the lining section.

[0018] (5) Structural performance parameters selected based on step (4) DI and ground motion intensity parameters IM , establish the seismic probability demand model of the tunnel under different erosion conditions (such as Figure 2 ), and then the key parameters of the fragility curve are calculated through the function obtained by linear regression: IM The median of the values ​​and the logarithmic standard deviation of the seismic probability demand model.

[0019] (6) Based on the key parameters obtained in step (5), establish tunnel vulnerability curves under different chloride ion corrosion conditions (e.g. Figure 3 ), the formula of the vulnerability curve is as follows: in When the earthquake is of a certain intensity IM When a certain damage state is exceeded d si The probability of represents the standard normal density cumulative probability function; is the earthquake intensity index threshold corresponding to each damage state obtained in step (6); is the total logarithmic standard deviation, which shows the variability of the curve and is obtained by the following formula.

[0020] in , , 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. and Value: , . The value of is obtained from step (5).

[0021] (7) Based on the empirical functional recovery curves of tunnel structures under three damage states, namely, slight damage, moderate damage, and severe damage, provided by the Federal Emergency Management Agency (FEMA), the tunnel functional recovery curves Q under different service times were established. (t) The formula is as follows: in represents the function of the tunnel at time t and damage state i, The tunnel is subjected to earthquake intensity IM In case of The probability of destroying the state.

[0022] (8) Based on the tunnel time-varying vulnerability curves under different erosion conditions obtained in step (6) and the tunnel function recovery curve obtained in step (7) Q (t) , quantitatively evaluate the seismic toughness of tunnels Re , and obtain the seismic toughness curve of the tunnel (such as Figure 4 ), the calculation formula of the toughness curve is as follows: in For earthquake events, The time it takes for the tunnel function to be fully restored.

[0023] pass Figure 4 The 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 there is no earthquake, the seismic toughness Re value of the tunnel is equal to 1. As the seismic intensity 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 ​​with a service time 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 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 corrosion conditions and quantitatively analyze its time-varying law, so as to reasonably evaluate the earthquake risk of the tunnel. This method is particularly suitable for areas prone to earthquakes. It can fully consider the impact of the service life of the shield tunnel and provide important guidance for the time-varying seismic toughness analysis, emergency rescue and disaster relief, and tunnel function restoration of the tunnel.

Claims

1. A method for analyzing time-varying seismic toughness of shield tunnels considering chloride ion erosion, characterized in that: The steps include: (1) Determine soil conditions and tunnel physical and mechanical parameters based on actual projects, and select seismic records according to specifications; (2) Determine the initial corrosion time of 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), a finite element dynamic analysis model of the soil-tunnel system under different erosion conditions is established and its dynamic response is calculated; (4) Using relative bending moment ratio and peak acceleration as tunnel structure performance parameters and ground motion intensity parameters for vulnerability analysis; (5) Based on the results of step (3) and combined with step (4), a seismic probability demand model of the tunnel under different erosion conditions is established to obtain the key parameters of the fragility curve; (6) establishing a time-varying seismic vulnerability curve of the tunnel under different erosion conditions based on the key parameters obtained in step (5); (7) Establish tunnel function recovery curves under different service times; (8) Based on the fragility 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 time-varying seismic toughness analysis method for shield tunnels considering chloride ion corrosion as claimed in claim 1 is characterized in that: In step (3): Based on the soil conditions, tunnel physical and mechanical parameters and seismic waves determined in step (1), and using the initial rust time of the lining and the performance degradation model of the steel bar and protective layer concrete under the influence of chloride ion corrosion determined in step (2), a finite element dynamic analysis model of the soil-tunnel system under different chloride ion corrosion conditions is established, and its dynamic response is calculated.

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

4. The time-varying seismic toughness analysis method for shield tunnels considering chloride ion corrosion as claimed in claim 1 is characterized in that: In step (5): Based on the structural performance parameters selected in step (4) DI and ground motion intensity parameters IM , establish the seismic probability demand model of the tunnel under different erosion conditions, that is, IM-DI All the calculation results of step (3) are plotted on the coordinate system and linear regression is performed. Then, the key parameters of the fragility curve are calculated using the function obtained by linear regression: IM The median value and logarithmic standard deviation of the seismic probability demand model β D ; The seismic probability demand model is as follows: Where a and b are the parameters obtained from regression analysis.

5. The time-varying seismic toughness analysis method for shield tunnels considering chloride ion corrosion as claimed in claim 1, characterized in that: In step (6): Based on the median and logarithmic standard deviation obtained in step (5), a tunnel time-varying vulnerability analysis model is established, i.e., the tunnel time-varying vulnerability curve under different erosion conditions. The formula is as follows: in When the earthquake is of a certain intensity IM When a certain damage state is exceeded d si probability; represents the standard normal density cumulative probability function; is the earthquake intensity index threshold corresponding to each damage state obtained in step (6); is the total logarithmic standard deviation, showing the variability of the curve, and is obtained by the following formula; in , , They represent the uncertainty of damage state definition, uncertainty of tunnel seismic response and bearing capacity, and uncertainty of ground motion. and Value: , , The value of is obtained from step (5).

6. The time-varying seismic toughness analysis method for shield tunnels considering chloride ion corrosion as claimed in claim 1, characterized in that: In step (7): Combined with the empirical functional recovery curves of tunnel structures in three damage states, namely, slight damage, moderate damage, and severe damage, provided by the Federal Emergency Management Agency (FEMA), the tunnel functional recovery curves Q under different service times are established. (t) , the formula is as follows: in represents the function of the tunnel at time t and damage state i, The tunnel is subjected to earthquake intensity IM In case of The probability of destroying the state.

7. The time-varying seismic toughness analysis method for shield tunnels considering chloride ion corrosion as claimed 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 curve obtained in step (7) Q (t) , quantitatively evaluate the seismic toughness of tunnels Re , and its calculation formula is as follows: in For earthquake events, The time it takes for the tunnel function to be fully restored; for t The structural performance at the moment is calculated as follows: in Indicates that the tunnel is t Moment and i Function in damaged state, is the exceedance probability of a certain damage state.

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