Vertical dynamic impedance of a sand-filled nodular pile in saturated soil

A new type of composite pile called a sand-filled nodular (SFN) pile has been increasingly used as a foundation element in the southeast coastal region of China. This paper derives an analytical solution of the vertical dynamic impedance of a SFN pile in saturated soil. The accuracy of the derived solution was verified by degenerating the SFN pile into a general pipe pile. The feasibility of incorporating the thin-layer assumption in Biot theory was then examined and the results suggested that for soft soils with shear modulus less than 5 MPa, the thin-layer solution is sufficiently accurate to estimate the vertical dynamic impedance of a pile in saturated soil. A parametric study was further conducted to provide insight into the influences of pile geometries and sand fill properties on the vertical dynamic impedance of the pile. The results indicated that the pile geometries have considerable influence on the vertical dynamic impedance of SFN piles where pile rib length plays a most significant role.