Seismic Behaviour of RC Building with Raft Foundation in the Ganges Basin, India

Many highly populated and important cities of India are situated in the Ganges basin. Deep alluvium deposit of this basin enhances the earthquake vulnerability of these cities due to amplification of seismic energies in the case of an earthquake. Raft foundations are generally provided for critical facility buildings due to their perceived effectiveness against differential settlement during earthquakes. However, the literature available on seismic behaviour of buildings with raft foundation considering soil deformability is relatively limited. In this context, a full three-dimensional finite element model of a four-storeyed building with raft foundation considering the typical layered soil profile of the Ganges basin has been developed in this study. The effects of different seismic parameters on the structural responses and moments induced in the raft have been studied with ground motions from 10 different earthquakes. Since the alluvium deposit of the Ganges basin is prone to get liquefied, effects of liquefaction of soil on the building with raft foundation have been considered simplistically. The results show that the raft foundation reduces the lateral displacement of the structure considerably. However, an increase in the vertical settlement of the raft in case of liquefiable soil is a matter of concern.