Study On Seismic Damage Mechanism And Anti-Seismic Measures Of Tunnels Under Special Geological Condition

In recent years, earthquakes took place frequently, which not only brought about tremendous economic losses and casualties, but also destruct numerous underground and surface structures. Due to high restraints of surrounding rocks, the seismic capacity of tunnels are better than surface structures obviously. So tunnels and other underground structures can play key roles in the earthquake relief. But when the Magnitude is big, such as Japan Miyagi earthquake(M9.0) and China Wen-chuan earthquake (M8.0), and when the geological conditions that tunnels go through is complex, tunnels could also be severely damaged, which in turn influences the post-seismic emergency rescue. Therefore it is necessary to conduct more analysis on seismic damage mechanism and researches on anti-seismic measures. In this study, through prototype observation of the damage characteristics on mountain tunnels after Wen-chuan earthquake, theoretical analysis and numerical simulation are combined to conduct analysis on seismic damage mechanism and anti-seismic measures of tunnel structures in fault fracture zones and near soil-rock interface.According to the two damage mechanism of tunnel structure---inertial force damage and foundation failure, theoretical analysis on tunnels'damage pattern was did on two severely damaged tunnels such as Longxi tunnel and Longdongzi tunnel in Wenchuan earthquake. Then in order to find causes of damage, earthquake intensity, epicentral distance, the orientation of earthquake wave, fault fracture zones, the quality of surrounding rocks, instable side slopes, the size of tunnel's cross section and supporting pattern, the depth of tunnels, the geostress, the bedrock interface, the construction condition, et al are taken into account to study the failure modes and damage level of tunnel,Referring to the geologic data of Qingdao Jiaozhou Bay submarine tunnel that cross fault fracture zones and soil-rock interface, and the support parameter, a numerical calculation model is set up by ANSYS software, and the process of analysis and calculation is conducted by the finite difference software FLAC3D. Then the seismic damage mechanism and anti-seismic measures in fault fracture zones and near soil-rock interface were studyed. By adjusting the mechanic parameters of lining and surrounding rocks, this paper analyze the expand regularity of plastic zone in tunnel lining and surrounding rocks, the regularity of displacement and stress over time of the lining, from four different point of view-the stability of surrounding rocks, the quality of surrounding rocks, the mass density and rigidity of lining and surrounding rocks. Based on he seismic damage mechanism of tunnels, the traveling theory of seismic wave and the rock-structure interaction principle, theoretical analysis is conducted to the result of numerical simulation to study the seismic damage mechanism of tunnels in fault fracture zones and near soil-rock interface. What's more, some relevant anti-earthquake measures are put forward. The main conclusions of this paper is that:in fault fracture zones and near soil-rock interface, surrounding rocks instability resulting from ground motion and the huge earthquake inertial force can cause damage to tunnel lining, yet the latter is the primary reason; guaranteeing mass density and stiffness of tunnel lining to be the same as or similar to that of surrounding rocks is the most effective way in preventing tunnel damages; the anti-seismic capability of ductile tunnels with light weight is bigger than general tunnel. This research achievement can enrich theory on seismic damage mechanism and be conducive to anti-seismic design of tunnel structure.