Experimental Study On The Fault Rupture Of Overlying Soil Induced By Reverse Fault Slip

With the increasing extension of urban land utilization, industry and civil construction, urban lifeline engineering such as subway and pipelines, are inevitably adjacent to and to cross the widespread active faults throughout China. The fault rupture propagation of overlying soil induced by fault slip causes serious damage to the infrastructures, pipe line systems and tunnels, and gives a threat to the safty of human property and lives in China.In order to reveal the ground deformation and the fault rupture propagation of overlying soil induced by reverse fault slip, a series of1g model tests were performed. Main research works are as follows:(1) A test apparatus which could simulate the fault rupture propagation of overlying soil induced by fault slip was developed. The fault simulator could simulate a reverse and normal fault slip with uplifting rates ranging from0to6mm/s and different dip angles(30/45/60/75/90°), and the maximum thickness of soil is in600mm.(2) A method to obtain the displacement and strain of overlying soil during the fault movement by PIV technique was proposed. And the fault rupture propagation, the surface deformation profiles and the shearing deformation could be described accurately.(3) Nine tests on the fault rupture of overlying soil induced by reverse fault slip were carried out. The fault rupture propagation, the surface deformation profiles and the shearing deformation were studied, and the influence of the uplifting rates, thickness of soil, relative density of sand and inclined soils were comparatively analyzed. The test results show that:1) When the reverse fault slips, one major rupture would be developed and then one subsidiary rupture could also form. The angles of the rupture path are in accordance with the fault dip in the beginning, and the rupture path bends towards the hanging wall block during the development. When the vertical fault displacement reaches to5%of the thickness overlying of soil, the major rupture propagates to the ground surface. And the angles of rupture path while approaching the surface (β) are in good agreement with β=45°-φ/2+γ,where φ is the friction angle of the soil and y is the soil surface slope. 2) When the reverse fault slips, the overlying soil could be divided to three zones, i.e. the stationary zone in the foot wall block, the rigid zone in the hanging wall block and the shearing zone near the rupture path. The shearing zone is like an inverted triangle in general. As the vertical displacement of the fault increases, the shearing zone develops upward, the width of the shearing zone in the ground surface increases nonlinearly and growth rate decreases.3) As the vertical fault displacement increases, the ground ridging grows, the maximum scarp slope rises, the width of affected zone whose slope is greater than or equal to1/150increases to a constant. And the affected width of reverse fault with dip angle of60°is about1.0-1.3times of the thickness of overlying soil.4) The uplift rate (0.05/0.16/0.50mm/s) and the thickness of overlying soil (200/400/600mm) do not have a regular influence on the fault rupture propagation. And a greater relative density of sand leads to a bigger fault propagation distance, a bigger the maximum scarp slope, a smaller required vertical fault displacement for fault outcropping at the ground surface and a smaller affected width of reverse fault.5) The soil surface slope has a great influence on the ground deformation and the fault rupture propagation of overlying soil. A bigger soil surface slope leads to a bigger required vertical fault displacement for fault outcropping at the ground surface, and a bigger fault propagation distance. When the soil surface slope increases from0°to5°or decreases from0°to-5°, the maximum scarp slope and the affected width of reverse fault will increase.