Abstract:

The exit portal section of Nanping tunnel on LanzhouChongqing railway is located in Grade VI plasticflow ground with unsymmetrical pressure. Pipe plies are installed from the ground surface to control the collapse of the plasticflow ground; enlarged arch feet and strengthened reinforcement are adopted to control deformation and collapse; 3bench excavation method with core soil is adopted on basis of construction scheme analysis and strict monitoring is performed inside and outside the tunnel. In the end, the tunnel driving successfully passes the shallowburied Grade VI ground with unsymmetrical pressure.

Key words: plastic flow strata, tunnel under shallow cover, pipe pile, consolidation technology