Large-scale shaking table test on unlined tunnel in fault zone under threedimensional earthquake

A fault is a geological structure characterized by significant displacement of rock masses along a fault plane within the Earth's crust. The Yunnan Tabaiyi Tunnel intersects multiple fault zones, making tunnel construction in fault-prone areas particularly vulnerable to the effects of fault activity due to the complexities of the surrounding geological environment. To investigate the dynamic response characteristics of tunnel structures under varying surrounding rock conditions, a three-dimensional large-scale shaking table physical model test was conducted. This study also aimed to explore the damage mechanisms associated with the Tabaiyi Tunnel under seismic loading. The results demonstrate that poor quality surrounding rock enhances the seismic response of the tunnel. This effect is primarily attributed to the distribution characteristics of acceleration, dynamic strain, and dynamic soil pressure. A comparison between unidirectional and multi-directional(including vertical) seismic motions reveals that vertical seismic motion has a more significant impact on specific tunnel locations. Specifically, the maximum tensile stress is observed at the arch shoulder, with values ranging from 60 to 100 k Pa. Moreover, NPR(Non-Prestressed Reinforced) anchor cables exhibit a substantial constant resistance effect under low-amplitude seismic waves. However, when the input earthquake amplitude reaches 0.8g, local sliding occurs at the arch shoulder region of the NPR anchor cable. These findings underscore the importance of focusing on seismic mitigation measures in fault zones and reinforcing critical areas, such as the arch shoulders, in practical engineering applications.