عنوان مقاله [English]
three-dimensional analyses are conducted to study the effects of ground-motion the presence of velocity pulse on the pile responses in liquefiable soils. Liquefaction of soils is an important issue in geotechnical engineering. Soil liquefaction occurs when a saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress such as shaking during an earthquake or other sudden change in stress conditions. The forward directivity effect, which includes a large velocity pulse at the beginning of the velocity time history of the ground motion and contains most of the seismic energy from the rupture, is the most damaging phenomenon observed in near-field ground motions. To investigate the effect of near-field ground motions on the seismic response of a soil-pile system, a three-dimensional model consisting of the two-layered soil and the pile is used. Modeling is conducted by using the FLAC 3D software. The P2PSand model is applied for the modeling of sandy soil. P2PSand model refers to a Practical TWO-surface Plastic SAND constitutive model for general 3D geotechnical earthquake engineering applications aimed at capturing essential soil dynamic characteristics. The model is a modified extension of the fabric-dilatancy-related sand plasticity DM04 model developed by Dafalias and Manzari. The Dafalias-Manzari two-surface model (DM04) is a critical-state compatible and state parameter-related plasticity model developed in the framework of Bounding Surface theory, which has been widely implemented and studied. Dynamic analyses are conducted for the soil-pile system under the excitations of four selected ground-motion suites that they were recorded on the rock. The results show that near-field velocity pulses have a considerable effect on the behavior of the system, and cause sudden large displacement demands on the piles and soil. The pulse in the record of near-field ground motion has caused the pore water pressure coefficient (Ru) to increase and liquefaction in the upper soil layer.