AN ANALYTICAL MODEL TO PREDICT SOIL REACTION INDUCED BY HARMONICALLY LOADED PILES

The theoretical representation of the dynamic horizontal soil reaction to a laterally oscillating pile using an approximate 3D continuum modelling is investigated. The governing elastodynamic equations are reduced by setting the vertical normal stresses in the soil equal to zero. Such a mathematical artifice uncouples the equilibrium in vertical and horizontal directions and allows the solution to be obtained in closed-form. This approximation is physically motivated, and conforms to the presence of a free soil surface and ultimately leads to a weaker dependence of soil response to Poisson’s ratio which is in agreement with numerical solutions from literature. This stress condition was not adopted in earlier studies by Tajimi and Nogami and Novak. The stresses and displacements in the soil and the corresponding reaction to a harmonic pile motion are obtained using pertinent eigenvalue expansions over the vertical coordinate. Piles of finite length embedded in a homogeneous soil stratum over rigid base are considered. Numerical results are presented in terms of dimensionless parameters and graphs that highlight salient aspects of the problem. A new frequency parameter is introduced to show that the popular dynamic plane-strain model yields realistic values for the soil reaction factor only at high frequencies.