Deformation and Mechanism Analysis of Tunnel Surrounding Rock Crossing Active Fault Zones

In order to study the deformation and failure mechanism of surrounding rock in tunnels crossing active fault zones， the Dongmachang No. 1 Tunnel of the Huali high-speed railway was taken as an example. The deformation behavior of the surrounding rock in the tunnel crossing an active fault zone was analyzed through field monitoring data， and the failure characteristics of the supporting structure were summarized. Based on relevant standards， the large deformation mechanism of the tunnel surrounding rock under the influence of the active fault was proposed. The analysis results showed that the deformation of the surrounding rock in the tunnel crossing an active fault zone was mainly the arch roof settlement. Large deformation was concentrated both in the highly fractured fault-influenced zone and in the tunnel exit section with high ground stress. The proportion of soft rock in the surrounding rock was relatively high （68.9%）， and cracking and rheological deformation of the supporting structure were severe. The overall strength-to-stress ratio of the surrounding rock was less than 0.25， the deformation rate exceeded 50 mm/d， and the total deformation exceeded 500 mm， indicating strong and large deformation. The deformation mechanisms of the surrounding rock included the fracturing and weathering of the rock mass in the fracture zone and its affected zones， the plastic flow mechanism of soft rock under high ground stress， and the plastic extrusion mechanism at soft-hard contacts or within soft interlayers in the soft rock mass.