Shake table study on seismic soil-pile foundation-structure interaction in soft clay

Seismic soil-pile foundation-structure interaction (SSPSI) especially in soft clay or liquefaction susceptible ground was reported as a key factor in seismic design by many investigators. Present study attempts to examine the influence of SSPSI on design response of pile foundation supported building structure embedded in soft clay through scaled model experiments using shake table. Study considers parametric variation of model superstructure and pile foundation in soft homogenous kaolin bed for developing an insight into seismic behavior of spectrum of structural systems under swept sine motions. Dynamic characteristics and acceleration response of model soil-pile foundation-structural systems are recorded in time and frequency domain in order to study the influence of SSPSI. Results indicate that shorter period superstructure system supported on pile foundation with relatively lesser lateral stiffness exhibits significant lengthening of period as compared to counterpart structure supported by higher foundation stiffness. Acceleration recorded at superstructure is found to be increased for shorter (0.3-0.4 secs) period structures due to SSPSI effect compared to fixed base condition irrespective of pile groups. Whereas, the acceleration recorded at pile head supporting short period structure exhibits subdued response compared to fixed base consideration. On the other hand, pile head acceleration is observed to be higher for moderate range (0.5-0.7 secs) of building structures for applied steady state motion which may be due to involvement of increased inertial forces.