Performance of soil-pile-structure systems under seismic waves

The dynamic behaviour of soil-pile-structure systems under the action of seismic waves is investigated through shaking table tests. Following a brief review of the subject, the work at hand focuses on the results of experimental tests carried out on scaled models performed on the 3m x 3m shaking table of the Bristol Laboratory for Advanced Dynamics Engineering (BLADE), University of Bristol, UK, within the framework of the Seismic Engineering Research Infrastructures for European Synergies (SERIES), funded by the 7th FP of the European Commission. The experimental program was aimed at investigating the seismic response of pile groups in stratified soil deposits in order to provide a benchmark for the calibration of numerical models. The test program encompasses different system layouts and loading conditions, namely: (1) pile head conditions (free head, short cap, long cap), (2) dynamic properties of the superstructure and (3) input ground motions (white noise, sinedwells and actual recorded motions from the Italian database). The model piles are embedded in a bi-layered subsoil made of two different dry Leighton Buzzard (LB) sands. The bottom layer consists of a mixture between LB-Fraction B and LB-Fraction E sands. The top layer is made of LB-Fraction E sand. The soil-structure systems were tested dynamically using an equivalent shear beam container (shear stack) of dimensions 1.19m long by 0.814m high by 0.550m wide, installed on the shaking table of BLADE. The tests were aimed at identifying: (1) the natural frequency of soil, (2) the impedance functions (stiffness and damping) of piles, (3) the kinematic interaction coefficients in the horizontal and vertical directions; (4) soil-pile-structure interaction effects in terms of natural frequencies and damping ratios with and without SSI. The results of the experimental investigations aim at providing a deeper understanding into the physics of dynamic response of soil-pile-structure systems.