NUMERICAL EXPERIMENTS INTO GROUP EFFECTS ON THE RESPONSE OF PILES TO LATERAL LOADING

Abstract The response of closely spaced piles subjected to lateral loading in either one or two rows has been analyzed using a three dimensional finite element model. This research is an extension of the work described in reference (7), which describes the finite element model and the response of a single pile to lateral loading. The model utilizes two types of plasticity models for soil to represent either undrained loading of saturated clay or drained loading of sands. Additionnally, frictional interface elements are used to provide for slippage and gapping at the pile-soil interface. The model is used to evaluate the effect of spacing within a row and between rows of piles on the p-y curves derived from the bending stresses within the piles, so as to provide information useful in developing design guidelines. The results of the analyses provide insight into the deformation patterns and development of areas of plastic deformation around the piles. The effect of pile spacing within a single row of piles (or the front row of a group) is seen to be relatively small for piles spaced at 3 diameters on center or more in undrained clay soil. The influence of pile spacing in a single row in sand is somewhat larger, but still relatively small at spacings of 3 diameters on center or more. Where multiple rows of piles are loaded such that one row trails another, the trailing row of piles is subject to a significant reduction in stiffness. Such patterns are in general agreement with the observations of field experiments. The p-y curves derived from the piles in each case are compared so as to provide guidelines for modification of design p-y curves to account for group effects.