Cyclic P-Y Curves for a Pile in Cohesive Soil

A lateral load test was performed on a full-scale steel pipe pile installed in a soil profile consisting of cohesive, fine-grained soils with occasional sand layers. The pile was loaded in nine increments from 0 to 89 mm of displacement, with 15 loading cycles applied for each increment. P-y curves representing static monotonic and cyclic loading conditions were derived from strain gauge data using a moving cubic polynomial technique. The results of push-over analyses using the derived p-y curves as input agreed well with the measured load-displacement response. It was observed that the cyclic p-y curves exhibited a sharp concave-up shape which contrasted with the broader concave-down shape of the static p-y curves. The cyclic p-y curves also exhibited lower peak resistances relative to the static p-y curves. The initial portion of the cyclic p-y curves is relatively flat with near-zero resistance which represents gapping of the soil. The displacement at which the soil reaction component of the cyclic p-y curves begins to dramatically increase is a function of the maximum displacement during previous loading cycles. It was also observed that the effects of cyclic loading were more pronounced in shallower soils.