Numerical modelling of normal fault- shallow foundation interaction emphasizing on the effect of alluvium depth

Shallow sediments and large displacement of the fault in bedrock can make the fault activity may appear to be surface faulting. Propagation of the fault rupture through the soil layer is one of the hazards associated with the fault dislocation in bedrock. The ruins from the 1999 earthquakes in Turkey and Taiwan and the 2008 earthquake in Wenchuan of China clarified the effect of fault rupture on the structures located near the fault trace on the ground surface. Also, previous studies have revealed the destructive effects of the impact of surface faulting on a structure. It seems that the alluvium depth can affect the interaction between the structures and faults. Therefore, the present study used a numerical model validated with centrifuge test results to evaluate the effect of alluvium depth on the response of shallow foundation-normal fault interaction. The Mohr-Coulomb constitutive law, with internal friction angle and dilation angle softening behavior, was used to model the interaction. The alluvium depth was considered as 15, 20, 30, and 40 m. The foundation was assumed to be rigid in all cases. It was placed at different positions relative to the free field fault outcrop on the ground surface. Normal faulting also was applied pseudo-statically to the model boundaries at a dip angle of 60°. The rotation of foundation and the vertical displacement profile of the ground surface was investigated to evaluate the effect of alluvium depth on the fault rupture and foundation interaction. The results show that there is no difference between the free-field faulting zones for different alluvium depths of loose soil. A graben is formed for deeper alluvium depths of dense soil in agreement with the analytical models, although the width of faulting zones is the same for different alluvium depths. It should be noted, a graben may form in a low-angle dipping normal fault (i.e. <60°) for loose sand. In interaction models, it has been observed that the interaction mechanism of the foundation and fault remains constant for both dense and loose sands. The footwall, gapping, and hanging wall mechanisms were formed for all alluvium depths related to the position of the foundation. Also, a graben was observed as one of the hazards associated with the normal fault rupture and shallow foundation interaction in the deeper alluvium depth of dense soil. By increasing the weight of the structure, the foundation experienced more rotation for 15 and 20m alluvium depths. The reliable foundation rotation could be estimated by considering alluvium depths of 20 m and more for both dense and loose sands.