Abstract:

In order to study the expansion method of shallow buried bias tunnel under the actions of seepage or fluidsolid coupling, taking Songjiagou No. 1 Tunnel of Zhongliangshan in Chengdu-Chongqing High-speed as the engineering background, to the shallow buried bias tunnel under the seepage action, four kinds of the extension methods such as left side of small interval extension, right side of small interval extension, left side of in situ extension, right side of in situ extension are studied numerically. In these expansion methods, the factors such as vault subsidence, surrounding rock convergence, initial support internal force, pore water pressure reduction are analyzed. By comparing the monitoring data in tunnel expansion construction, it was found that the numerical simulation results are extremely consistent with the construction monitoring data, which proves the reliability of the calculation results. According to the comparative analysis of the four extension methods, it is concluded that: (1) By using the method of small interval extension, the factors such as surrounding rock convergence deformation, surrounding rock vertical stress and so on are all smaller than those of the in situ extension. (2) From the perspective of the groundwater resource protection, the protection effect by adopting the extension method of left side small interval is obviously better than the other three extension methods. (3)The pore water pressure reduction of surrounding rock shows obvious gradient change in all directions, and during the tunnel construction, the water surge mostly comes from the upper part of surrounding rock in extended tunnel.

Key words: shallow buried bias tunnel, fluid-solid coupling, tunnel extension method, numerical analysis