Preceding Reinforcing Improvement Research on the Tunnel with Low Permeability Stratum

Research purposes: When Wuhan metro line 2 went through poor permeability of clay or clay gravel stratum,as a conventional construction method, " small duct grouting in advance" in tunnel arch was difficult to construct,and its advanced reinforcement effect was not obvious. In order to solve this problem,this paper put forward a scheme that the application of steel instead of leading anchor rod or steel tube. By comparing arching effect between rectangular cross- section steel and circular cross- section steel,this paper suggested to adopt the rectangular cross section steel.The results show that the rectangular cross- section steel could improve strengthening effect. And it can accumulate the experience to similar projects.Research conclusions: According to the research,it can be drawn:( 1) For the same width and spacing of the rectangular and circular cross section steel,rectangular steel has better the arching effect,and it can bear higher soil load;( 2) In terms of the bending capacity and price,rectangular section steel is better than that of circular steel tube;( 3) In the small percolation coefficient strata,grouting effect is poor,rectangular steel can be used in place of the small duct grouting in advance for supporting in advance;( 4) The research results can be applied in the tunnel advanced support design.