Behavior of circular tunnels crossing active faults

Abstract

A review of seismic damages suffered by underground structures shows that most tunnels were located near active faults. In a near field seismic event, the rupture of an earthquake fault generates large ground displacements referred to “fling step” effects. The present study investigates the response of tunnel to static fault displacement according to different earthquake magnitudes by using a 2D finite elements program. The results indicate that the fault mechanism, tunnel position, amount of slip, and earthquake magnitude have significant effects on tunnel lining response, making considerable changes in sectional forces, displacement, and shear distortion on tunnel lining. Reverse faults have more effects on sectional forces of lining comparing to normal faults. The displacement of the lining section under reverse faults is greater than the one under normal faults, except for earthquake magnitudes greater than Ms 7. The shear distortion of the lining section under normal faults located in hanging wall side (i.e. moving bottom boundary of faulting) is higher than the one in footwall side (i.e. fixed bottom boundary of faulting). This is opposite for reverse faults. Finally, in normal mechanism, the recommended safe distance from fault tip is smaller than that of reverse mechanism.