Seismic Response of Circular Tunnels in Jointed Rock

Although deformation along a weak joint under a strong seismic event can seriously damage the tunnel, the effect of joint has not yet been well understood or quantified. We perform a series of pseudo-static discrete element analyses to evaluate the effect of deformation along rock joint on the seismic response of circular tunnels. We also perform parallel continuum analyses to compare and quantify their differences. A comprehensive set of joint parameters are considered in this study. The results illustrate that the joint significantly increases the moment demand in the tunnel lining, whereas it has a secondary influence on the thrust. The joint stiffness and shear strength have critical influence on the tunnel response. Widely spaced joint set produces a larger tunnel response. The tunnel response is highest for vertical and horizontal joints, and the lowest when the joint dips at an angle of 45°. The moment in jointed rock may be 20 times higher than that in intact rock. The pronounced deviation from continuum analyses highlights the need to estimate the influence of discontinuities on the seismic response of underground tunnels from discrete element analyses. This may be of concern for critical structures such as nuclear facilities.