Torsional dynamic response of a pile embedded in layered unsaturated viscoelastic soils

The dynamic response of the pile is significantly influenced by load types (e.g., horizontal, vertical, and torsional) and the complexity of geological conditions (e.g., moisture content and heterogeneity). In this study, an analytical model is presented to analyze the torsional vibration of a pile in layered unsaturated viscoelastic soils. To accurately capture the layering of unsaturated soil, the pile-soil system with multiple layers has been developed. The variable separation method is employed to obtain the general solution for the circumferential displacement of each soil layer. Utilizing the continuity conditions at the pile-soil interface, the general solution for the circumferential displacement of each pile section is then derived. Furthermore, the impedance transfer function method has been used to acquire the torsional dynamic response solution for the whole pile-soil system. The results indicate that the degree of saturation and shear modulus of the soil near the surface have a significant impact on the torsional impedance of the pile, while the influence of the permeability coefficient is slight. The presented model has also been applied to simulate the rise of groundwater levels in actual field soil. The results indicate that the torsional impedance decreases gradually as the groundwater level rises.