چكيده به لاتين
The purpose of this study is to investigate the capability of the Beam on Nonlinear Winkler Foundation (BNWF) method to model pile groups in improved soft clay under lateral quasi-static and seismic loading. The soil profile consisted of four lightly overconsolidated soft clay layers overlaid on dense sand. The pile group included 4 steel pipe-piles in a symmetrical 22 configuration and with a center-to-center spacing of 3D and 7D, where D is the pile diameter. To model the seismic behavior of the pile group, the nonlinear seismic response of the ground was first obtained (in DeepSoil). The obtained displacement-time histories were then fed into the Winkler elements at different depths along the pile. Comparing the predicted and centrifuge-measured results indicated a reasonable agreement for the free-field and pile group response, validating the utilized BNWF model. Parametric studies showed that when the predominant period of an earthquake gets closer to the fundamental period of the pile group system, the response of the pile group becomes stronger. Clay improvement, however, reduced the acceleration, displacement, and the maximum bending moments of the piles compared to those for piles in unimproved clay. Parametric studies indicated that the reduction in acceleration and displacement of the cap and the maximum bending moment of the piles can be up to 30%, 17%, and 69%, respectively. This decrease in response was due to the reduction of spectral parameters (acceleration and displacement) of the improved soil compared to the unimproved soil. To accurately predict the response of the pile group in the improved soil, the nonlinear response of the soil should be estimated considering the soil improvement and using the improved soil parameters. According to the inherent assumptions in modeling by BNWF, the dimensions used for the CDSM block (23D 23D 9D) can be considered as "infinite" dimensions under seismic loading conditions such that soil improvement in larger dimensions may not be further useful in terms of pile response improvement.
