Numerical analysis of rate-dependent reaction of pile in saturated or liquefied soil

The purpose of this study is to clarify the loading rate dependency of subgrade reaction of a single pile in saturated or liquefied soil. The parametric studies were performed by incorporating the soil-pore water coupled formulation and a newly proposed constitutive model for sand. The model can explicitly treat the degree of liquefaction by changing the lower limit of the mean effective stress. The liquefied soil at a certain depth around a pile is modeled with finite elements under plane stress condition. The subgrade reaction of a pile is calculated under various loading frequencies, permeability and degrees of liquefaction. The results of the parametric studies show that the subgrade reaction varies with loading rates, permeability and degrees of liquefaction, and the dimensionless subgrade reaction normalized by that without seepage has a unique relation with dimensionless time factor which consists of pile diameter, loading rate, permeability coefficient and coefficient of volume compressibility.