Characterization of Mechanical Behavior of Ultra-Small Clearance Tunnel Construction in Upper Soil and Lower Rock Composite Strata

It is hard to grasp the deformation law of surrounding rock and force characteristics support structure during construction ultra-small clearance tunnels in upper soil lower composite strata. Based on tunnel Li Shuping, Tongxin Expressway, Guizhou, this paper adopted a combination numerical simulation field monitoring analyze influence different burial depths soil-rock interface positions internal forces tunnel. The conclusions are: (1) data show that stress steel frame leading increases first by proximity construction, then decreases reaches stable value after secondary lining applied, at arch waist soft layer furtherest from side middle column greater than column; (2) position has significant initial tunnel, bending moment with downward movement increase depth; (3) point which attention should be paid construction; (4) when located below foot arch, following will larger results can provide reference for design strata