STUDY OF FLAT RATIO OPTIMIZATION OF LARGE-SPAN TUNNEL SECTION IN SHALLOW BROKEN ROCK MASS

The design of reasonable flat ratios for flat and large span shallow tunnel has very important effect on cost saving and expense reduction for ventilation and lighting.Therefore,optimizing the flat ratios of shallow large-span tunnel is the key problem faced by the tunnel design and construction.Firstly,program with the standard design language Python of general-purpose finite element software ABAQUS to achieve parametric design for the different flat ratios of large-span Panlong tunnel in shallow broken rock mass planned to be constructed in Qingyuan City.Then,the stability and deformation failure of tunnel structure under 5 kinds of flat ratios are researched.Target values of excavation area,horizontal convergence,ground surface settlement,vault subsidence,etc.which affect the stability of flat tunnels,are optimized using the analytic hierarchy process(AHP) and determining their weight vectors.Finally,the optimal flat ratio under supported project is put forward.The results and method of this paper provide reference for the section optimization design of tunnel engineering in equivalent conditions.