Tunnel Lining Stability and Structural Damage Threshold under Seismic Loading

To analyze the damage distribution characteristics and ultimate bearing capacity of tunnel linings under seismic action, damage variables were introduced into the Mohr-Coulomb constitutive model. Thus, an incremental elastic–plastic damage constitutive model for concretewas constructed. Uniaxial tensile and compressive tests were performed to verify model reliability, and the damage thresholds for different strength classes of concrete under the test conditions were numerically obtained when destruction occurred. These damage thresholds were considered as the criteria for material failure to solve the ultimate bearing capacity and failure form of the tunnel structure. Calculation results demonstrate that as the peak ground acceleration increases, the shallowly buried tunnel structure presents the three following stages: elastic bearing, local instability, and overall instability. If the compression or tensile damage values of an element exceed the threshold value, the element is regarded as destroyed. The failure of any element of a structure can be used as a criterion for local instability. If the volume of the destroyed elements exceeds 10% of the overall volume of elements, and the proportion of destroyed elements in the lining shoulders and side walls begins to abruptly increase, the structure can generally be regarded as unstable.