ROCK DYNAMIC RESPONSE OF RAILWAY TUNNEL TRAVERSING THROUGH FAULT UNDER STRONG EARTHQUAKE

Usually, the earthquake-induced damage to underground structures is lighter than that to above-ground structures. But, under the condition of strong earthquakes and faults, the earthquake-induced damage to underground structures is still considerably serious. On May 12, 2008,Wenchuan earthquake with a magnitude of Ms 8.0 in Sichuan province, China caused tremendous damage to underground structures, especially the tunnels of railways and roads that traverse active faults. Dengjiaping tunnel of Cheng-Lan Railway(Chengdu to Lanzhou, in China) traverses the central fault belt in Longmenshan zone with complex geological conditions and developed active faults. This study uses dynamic module of 3 Dimensional Discrete Element Code(3DEC) and acceleration histories of Wenchuan earthquake in Qingping station to investigate the dynamic response process of Dengjiaping tunnel under the combined effects of strong earthquake and fault. Verified by comparing the ground motion of field survey and modeling results, the modeling results have high reliability. The modeling results show that the combined effects of strong earthquake and fault disturb the initial field stress distribution and cause the stress accumulation and stress concentration of tunnel surrounding rock near faulting zone. The high stress concentration results in fault gradual rupture and tunnel gradual failure, which can be qualitatively divided into 5 stages: 1)elastic stress accumulation, 2)local rupture beginning, 3)rupture growth at high speed, 4)spontaneous rupture growth, 5)gradual stability state. This study is helpful to understand the dynamic response process of tunnel surrounding rock under the combined effect of strong earthquakes and faults, and has considerable significance for tunnel safety estimation.