Dynamic Behavior of Pile Groups in Inhomogeneous Soil

Abstract

An efficient method of analysis has been developed to determine the steady‐state dynamic response of vertically loaded piles and pile groups embedded in a soil stratum in which the stiffness increases linearly with depth. The piles have been represented as compressible columns and the soil as a hysteretic semi‐infinite medium. The results of the analysis have been plotted in nondimensional form to demonstrate the effects of key nondimensional parameters on the vertical response of the pile‐soil system. From the results of analyses of two pile groups, dynamic interaction factors have been calculated. These factors are very different from the interaction factors for homogeneous soils, particularly if the piles are widely spaced. These interaction factors reveal that piles in groups are subject to out‐of‐phase motions, which may result in substantially reduced pile group settlements at certain frequencies. Illustrative results for four and nine pile groups are given, as well as a practical design example.