Dynamic coupled analysis of large-diameter steel piles located in liquefiable soil layers

Many shores in Iran are at risk of earthquakes, and due to the dynamic loading of the earthquake, these saturated soils are prone to liquefaction. In this study, the behavior of two-layered saturated sand with different relative densities and the interaction effects of soil and pile under dynamic loads has been considered. For this purpose, a constitutive model presented in the multi-surface framework has been applied. Also, the equations governing the saturated environment have been solved in a completely coupled way based on the finite element method. According to the obtained results, liquefaction will occur in the upper layers no matter the loading frequency when their liquefaction potential is high. Nevertheless, at depths and layers where the liquefaction potential is low, the pore pressure is strongly dependent on the loading frequency, so that with an increase in the frequency of the dynamic loads, the water pore pressure increases less. Also, based on the analyses performed under different frequencies, it is observed that at a dynamic loading frequency, increasing the pile length has little effect on the displacement of the pile head but can significantly affect the displacement of the buried parts. Therefore, the larger the ratio of the pile length in the liquefiable soil to the total length of the pile, the greater the possibility of more displacement in the buried end of the pile; And as a result, it can lead to instability of the structure.