Back-calculations of Centrifuge Tests on Pile Groups Subjected to High-cyclic LoadingÂ-Paper

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The study evaluates a finite-element method for predicting the response of piles in sand under repeated lateral loading. The authors back-calculated centrifuge tests on a single pile and a five-pile group, subjected to as many as 500 cycles. The tests were conducted at 100 g, and the selected cyclic load level was 20% of the reference ultimate lateral load.<br /><br />The simulations used numgeo and combined a hypoplastic soil model with an Intergranular Strain extension for the initial, low-cycle response and a High-Cycle Accumulation (HCA) model for longer-term deformation. Model parameters were calibrated using laboratory tests on the same silica sand, with a simplified calibration procedure for the HCA model. The pile-group geometry was modelled in three dimensions, using symmetry and an adaptive strain amplitude in the HCA calculations.<br /><br />The simulations reproduced the single pile’s initial cyclic response and stiffness reasonably well, and captured the approximately linear accumulation of displacement with cycle count through roughly 100 cycles. At higher cycle counts, the predicted single-pile accumulation increasingly diverged from the measurements and was too large overall.<br /><br />For the pile group, the model captured accumulated displacement trends satisfactorily, but predicted the initial load–displacement response to be substantially too stiff: the simulated displacement after the first cycle was about 8 cm, compared with 17 cm measured. The monotonic single-pile response was also reproduced well over the simulated range, although the calculation stopped before reaching the experiment’s very large displacements because of convergence difficulties.<br /><br />Overall, the combined numerical strategy shows promise for estimating cyclic displacement accumulation in pile groups. The authors identify full HCA-model calibration and explicit consideration of pile-installation effects as priorities for improving agreement, particularly for the single pile’s accumulated deformation and the pile group’s initial stiffness.

Keywords

finite element method

lateral loading

pile response

sand

cyclic loading

centrifuge tests

pile group

hypoplastic soil model

high-cycle accumulation

displacement accumulation