ABSTRACT
Deep foundations, like conventional pile foundations and the relatively new combined pile-raft foundation (CPRF), which is a hybrid of shallow and deep foundation, are widely used for both offshore and onshore structures to transfer superstructure load to the deeper strata. They are generally preferred where topsoil is loose, soft, and susceptible to shrinkage and swelling, when shallow foundations experience huge uplift pressure due to a fluctuating water table and are not safe under serviceability conditions. Though reasonably good progress was made for the design of pile foundations and CPRF under lateral loads for static loading, their performance under seismic loading is an area of concern to geotechnical practitioners over the last few decades due to increasing demand for high-rise structures. The problem is more complex if the soil is susceptible to liquefaction during earthquake. More attention needs to be given to pile foundations as floating piles passing through liquefiable soil layers undergo significant loss of shaft resistance. In the case of end-bearing piles, excessive loads may be transferred to the end-bearing strata due to loss of shaft resistance, and thus the pile is subjected to higher bearing pressures. Also, loss of shear strength in the liquefied zone will increase the effective length of the pile, and thus the pile may fail by buckling if axial loads are predominant. In the case of CPRF, the presence of liquefied soil may alter load-sharing aspects on different components of the foundation system.
