Interaction between normal fault rupture and rigid strong raft

The incomplete understanding of the soil failure mechanisms during dip fault rupture event and the interaction of these mechanisms and the existing structures near or across the fault plane has led to inconsistent regulations for placing structures near active faults. In this study, centrifuge modeling was conducted to study the failure mechanisms and patterns of soil deformations during normal faults with a dip angle of 60° in a medium dense sand layer, and the fault interaction with the existing structures founded on rigid strong rafts near and across the fault plane. In the normal fault rupture event, inactive relatively vertical shear bands propagated from the fault point vertically in the model ground. Thereafter, an inclined shear band was formed in the upper half of the model ground, propagated downward to form with the other bands a cracked graben, and become the main slip surface in the failure mechanism. Some soil deformations took place in the relatively stationary soil mass outside the displaced soil zone and led to some settlements at the surface of that stationary soil near the fault. The main shear band inclination to the horizontal exceeded the dip angle. Rigid strong rafts diverted the fault rupture shear bands in the alluvium so as to bypass, rather than rip apart the rafts. The rafts tilted and slide on the foundation soil, during the fault rupture. The raft slide and tilt increased as the raft bearing pressure on the soil decreased. These observations matched the reported failure mechanisms, soil deformations and foundation failures in the field case studies.