Cyclic Behaviour of Pile Groups in Calcareous Sediments

Abstract

Two series of cyclic loading tests have been carried out on model pile groups jacked into reconstituted calcareous sand beds which were consolidated under different overburden pressures. The first series studied the effects of displacement-controlled cyclic loading on the reduction of skin friction of a model pile group. The results of these tests have shown that this reduction (or “degradation”) increases with increasing cyclic displacement and number of cycles. There is only a small effect of the number of piles in the group on reduction of skin friction. The second series of tests studied the effects of uniform cyclic load and non-uniform cyclic “storm” loading tests on the accumulation of permanent displacement of the model pile groups. The results of uniform cyclic loading tests have been summarized in a stability diagram for the pile group in which the influence of cyclic loading on the group capacity can be seen. The results of non-uniform cyclic loading tests have shown the effects of accumulated displacement of the capacity of the groups. The accumulated displacement of a pile group in load-controlled cyclic tests was found to be similar to that of a single pile, with increases in displacement caused by increasing load level being more significant than increases arising from increasing numbers of cycles. There was only a small influence of the number of piles on pile capacity and group settlement for both uniform and non-uniform cyclic loadings. A modified form of boundary element analysis was used to predict the cyclic behaviour of a pile group using input parameters derived from the experimental results for a single pile. Comparisons between the measured and predicted results have shown reasonable agreement.