Seismic Response and Damage Characteristics of the Shallow Tunnel with Asymmetric Loess Cover Under the Oblique Incidence of Seismic SV Wave

The instability of the shallow tunnel with asymmetric loess cover affected by the earthquake has been one of the most prominent geotechnical disasters in the loess region. Under the shallow-focus earthquake, the tunnel is subjected to obliquely incident seismic waves, and its seismic response is significantly affected by the non-uniform ground motion caused by the obliquely incident waves. This study introduces a method of inputting an oblique incidence of SV wave by programming with finite element analysis program ANSYS to a bias loess slope. With the proposed numerical method, the seismic response and damage characteristics of a shallow tunnel with asymmetric loess cover under oblique incidence of seismic SV wave are analyzed. The results show that: (1) The input method of oblique incidence of SV wave and its combination with the finite element model are feasible to analyze the seismic response and damage characteristics of the shallow tunnel with asymmetric loess cover. (2) The principal tensile and compressive stresses of tunnel lining are distributed in the shapes of a butterfly and an X, respectively. The symmetry axes of the stresses show the characteristic of bias. (3) With the increase of slope angle, the plastic zone increases and develops toward the slope surface. (4) With the increase of thickness of soil cover, the plastic zone decreases. (5) With the increase of incidence angle, the distribution of principal tensile stress develops to a circle, and a through plastic zone connecting the slope toe and springline at the shallow-buried side occurs.