Reasonable permeability coefficient and engineering measures of concrete lining circle

The analytical results of seepage fields and the elasto-plastic solutions considering seepage force are adopted to study the feasibility of permeable concrete lining and its reasonable permeability coefficient. The influence laws of seepage field, flow discharge, plastic zone, displacement and rock pressure are analyzed under different permeability coefficient ratios of lining to surrounding rock of free flow pressure tunnel running in a practical project. The results show that the pore water pressure, plastic zone, displacement at the edge of the plastic zone and rock pressure are the maximum when the lining circle is impermeable concrete material. But those values rapidly decrease when the permeability of lining slightly increases, and tend to be constant values with the increase of permeability coefficient ratios of lining circle to surrounding rock. The method of permeable concrete lining in free flow pressure tunnel is feasible, and the reasonable permeability coefficient ratio of lining and surrounding rock is equal to or larger than 1.0. The permeable concrete lining circle structure is proposed for solving the problems of limited flow discharge required by the surrounding water environment and durability of reinforced concrete lining. The design measures are also discussed.