Dynamic Response of Pile Foundations in Torsion

A theory is presented which facilitates the evaluation of torsional stiffness and damping of piles embedded in horizontally layered soils. This theory employs the matrix stiffness method and is an extension of a continuum approach presented earlier by the writers. Response curves for piled footings may be calculated using the data presented in the figures for stiffness and damping. The theory is compared with field experiments. The results of the experiments show good agreement with theoretical predictions. Dynamic properties of piles are found to be very dependent on the variation of soil properties with depth and on soil material damping. The importance of soil material damping is also demonstrated for shallow rigid footings vibrating in the torsional as well as rocking modes.