Experimental study on overlying soil rupture evolution and cross-fault tunnel failure mechanism under bedrock fault dislocations

Active fault dislocation is a key disaster-causing factor for seismic damage of underground structures. A 1∶80 geometrically similar semi-structural physical model test was conducted for urban shallow-buried cut-and-cover rectangular metro tunnels crossing active faults, considering four working conditions (normal and reverse faults with dips of 45° and 60°). The rupture extension laws of overlying sand under bedrock fault dislocation and the failure mechanism of cross-fault rectangular tunnels were systematically revealed, and the test results were compared with a rupture extension path prediction model based on the logarithmic spiral curve. The results show that: (1) Under normal fault dislocation, the initial and surface rupture angles of overlying soil are larger, while the shear zone width is smaller than those under reverse faults; (2) The presence of the tunnel significantly modifies the rupture path and displacement field, with the path tending to be straight under normal faults and slowing down near the tunnel under reverse faults; (3) Tunnel failure is dominated by tensile fracture, occurring at the footwall section under normal faults and the hanging wall section under reverse faults. The critical dislocation for failure is smaller under normal faults and decreases with increasing fault dip; (4) The logarithmic spiral prediction model agrees well with free-field test results, with relative errors of rupture angles within 12%. The findings provide theoretical references for the anti-dislocation design of metro tunnels crossing active fault zones.