Effect of soft soil layer on local dynamic response of floating pile under harmonic lateral loading

Abstract

Full-scale experiments of long floating piles under lateral harmonic excitation at the pile head were conducted to examine local resonant effects caused by the soft soil layer’s dynamic characteristic. Three 0.35 m diameter concrete piles with different lengths — 6, 10, and 15 m — in 19 m thick soft Bangkok clay were studied. Small-amplitude sweep excitations were applied in the frequency range that triggers resonance of the top soft soil layer, but will not reach the first fundamental frequency of the pile–soil system. The experiments show that the top soft soil layer produced local peaks of pile response at frequencies associated with predominant frequencies of the soil layer that agree well with the previous study of the dynamic characteristic of a soil layer in the Bangkok basin area by microtremor measurement. A comparison of experimental results with numerical solutions, i.e., the reduced dimension finite element model (RDFEM) and Winkler’s beam on spring and dashpot foundation (WBSDF), to evaluate their ability to simulate local resonance effects was carried out. Dynamic moduli of soil at different depths, to be used in numerical simulations, were measured by crosshole seismic test. Satisfactory matches between experimental results and numerical simulations by RDFEM were observed whereas WBSDF predictions are not close because the soft soil layer cannot be incorporated in WBSDF.