Study On The Seismic Response Of Tunnel Lining With Thin Lining And Back Cavity

The total mileage of operating tunnel in China has ranked first in the world. Although great achievements have been made in tunnel construction, there is a certain proportion of operating tunnels having quality defects, such as cavity behind the lining, inadequacy of lining thickness, lining crack and so on. The defects in tunnel will affect its seismic performance and increase earthquake damage to the lining structure. There is no doubt that the tunnels operating with defects will be at high risk in earthquake. In light of the reality that strong earthquake occur frequently in China and the defects of mountain tunnel are outstanding, the thesis makes a systematical study on the rule of seismic response of tunnel on condition of thin lining and cavity behind the lining. The effects that these defects impose on tunnel seismic performance have been analyzed in the thesis. The major research contents and research findings as follow:(1) On the basis of literature research, the thesis analyses the causes, the appearances and the distribution rule of tunnel defect. Based on the quality test result of an operating highway tunnel in Yunnan Province, the thesis summarizes and analyzes the features of lining defect. The results show that defects are common in operating tunnel, and it is easier to find quality defect on the tunnel vault and arch sides. When the thickness of lining is insufficient, cavity behind the lining is often to find.(2) Combine with the results of field survey and taking a two-lane high-way tunnel as the sample model, the author designed a vibration table model testing program. The vibration table model test was carried out on several different conditions:the tunnel without any defect, the tunnel lining is intact but there is a cavity behind the vault lining, and the lining thinning down and at the same time there is a cavity behind the lining. The test results indicate that cavity behind the lining and thin lining make a great impact on seismic response of tunnel, for instance, the seismic performance of the tunnel structure was significantly degraded, the seismic damage model of the tunnel was changed, and the location where the thin lining and cavity lie become the weak region of seismic resistance. In regard to the tunnel without defect, the tunnel structure began to appear cracks in high acceleration (0.6g); and damage appeared on tunnel vault and corner. When the dome is insufficient and empty, lining damaged when acceleration in the range of 0.2g-0.4g, whose destructive form appear mainly on tunnel vault and corner, which differs from the lining with intact structure.(3) ABAQUS software is applied to establish computing model of seismic response in which damages on lining structure have been took into consideration. Seismic response analyses on various defects combination conditions have been carried out in the study. The analysis results indicate that:Perfect tunnel has a good seismic performance, but the defects will change the stress state and stress distribution of the tunnel, and significantly reduce the seismic capacity of the tunnel. The most serious injury is the corner and arch waist.