Shaking table tests on seismic measures of a model mountain tunnel

A series of three dimensional (3D) shaking table tests were carried out to investigate the mechanism and effect of seismic measures of mountain tunnel using a scaled model based on a real tunnel. Key technical details of the experiment, including similarity relations, seismic measures simulation, boundary conditions, sensor layout, modeling methods, and ground motion input were presented. Main seismic measures, including reinforcing surrounding rock with anchors, increasing lining flexibility with steel wire mesh, and installing seismic isolation layer between reinforced surrounding rock and tunnel lining, were investigated in this study. Experiment results show that: (1) adding a layer of steel wire mesh in the tunnel lining can improve the flexibility and seismic performance and also may effectively prevent radial cracks from crossing the lining; (2) installing a geofoam isolation layer between the reinforced surrounding rock and the tunnel lining reduces dynamic earth pressure by 70-90% for the lining without a seismic isolation layer; (3) the flexible joints can effectively avoid global failures of tunnel lining for they reduce dynamic strain and bending force in the tunnel lining and decrease the seismic energy transmission along the lining in axial direction; (4) reinforcing surrounding rock with anchors significantly reduces dynamic earth pressure and strain of the lining by about 50%. In addition, the length of seismic reinforcement for general mountain tunnel portal is recommended to be 50 m from the tunnel portal along the axial direction.