Tunnel reinforcement by using pressure-induced inflatable pipes method

A new tunnel auxiliary method, the pressure-induced inflatable pipes method, is proposed in this paper. It utilizes the concept of cavity expansion for tunnel reinforcement by forming an umbrella arch on the roof of the tunnel. When each inflatable pipe is inserted and expanded by pressure in the boreholes of the umbrella arch, the ground around the borehole can be compacted so that the stress conditions above the tunnel perimeter are changed favorably. To verify the reinforcement effect of this new concept, a pilot-scale chamber test, numerical analysis, and trapdoor test were performed and compared. In the pilot-scale chamber test, three types of inflatable pipes were tested to check their capability for expansion and each type of pipe was demonstrate to function correctly by expanding only in the intended direction. Numerical analysis of a tunnel and the applied trapdoor tests using the inflatable pipes were also performed to determine the reinforcement effects of the proposed technique. The results imply that the new method with three-directional inflatable pipes can contribute to reducing tunnel convergence and face settlement.