A Few Critical Aspects to Rational Design of Piled Raft Foundation for Oil Storage Tanks

Some level of settlement is allowed in the design of oil tanks if uneven settlement is controlled within allowable values. Considering the critical condition of piled raft foundation (PRF), that is, secure contact of raft base to the ground surface, PRF is considered as one of the rational foundations for the oil tanks. However, PRF has a complicated interaction with soil under horizontal seismic loading, especially if the tank rests on a liquefiable soil which may cause an extreme change of the soil stiffness under the tank. Regarding this complexity, the main concern in use of PRF for oil tanks is proper design of this foundation system. In this study, a series of centrifuge tests were performed to investigate the mechanical behavior of oil tanks supported by PRF on non-liquefiable and liquefiable sand. Using the observed results, such as accelerations of the tank and ground, displacements of the foundation and excess pore water pressures of the ground, some practical hints for reasonable design of piled raft foundation for oil tanks on non-liquefiable and liquefiable sand are discussed. In case of PRF of oil tank on non-liquefiable sand, the main concern in the rational design of the foundation is piles’ design and their punching effect on the raft, while the major critical issue in case of PRF of oil tank on liquefiable sand, is reduction of piles bearing capacity during the liquefaction that absolutely affects the performance of piled raft foundation.