Research Study On Lining Optimization Design Of Qingdao Subway Based On Strength Reduction Method And Lining Safety Factor

The stability for the surrounding rock of underground tunnel is an interest question to manyscholars. The current lining structure calculation method has great artificiality and experience. Themain structure size of surrounding rock is mostly confirmed by engineering analogism or byconservative experiential formula. Because of conservative design, thick lining size is adopted atsome high quality rock mass. Qingdao has superior geological conditions, so how to make full usethis superiority to reduce the size of lining structure is of great significance to the subwayengineering of Qingdao.In this paper, the strength reduction method is used to analyze and evaluate the stability forthe surrounding rock of underground tunnel. The optimized design method of tunnel liningstructure is put forward, and the lining structure size is quantitatively determined to make sure thetunnel’s safety and to reduce the cost. The main contents of this thesis are as follows:(1) The FLAC5.0software based on the finite difference principle is briefly introduced. Thebasic principle of the shear strength reduction and the judgment on the basis of tunnel damage arealso briefly introduced. How to estimate the damage of the tunnel in numerical simulation ofFLAC is analyzed.(2)Two subway tunnels with different span in Qingdao are selected, and their safety factor iscalculated by strength reduction method. Different safety factors are obtained, including the nakedhole, surrounding rock with primary support, surrounding rock with secondary support and thesecondary support from Ⅰ to Ⅳ level. And then, the optimized design method of tunnel liningstructure of tunnel is presented.(3)A typical metro station with shallow tunneling method in Qingdao is selected as anexample, and its safety factor is calculated by strength reduction method. Different safety factorsare obtained, including the naked hole, surrounding rock with primary support and the secondarysupport of the station. And then, the optimized design method of tunnel lining structure of thisstation is presented.(4)Interval tunnels with different buried depths but the same span are chose to be analyzed.Safety factor of naked hole is obtained by strength reduction method. The value of safety factor increases first and then decreases with depth. The tunnel’s rational buried depth can be determinedbased on the changing law of safety facto.