Support Mechanisms of Rammed Aggregate Piers. II: Numerical Analyses

This paper is the second of a two-part series describing an investigation of the mechanical behavior of rammed aggregate piers in supporting rigid square footings. In this paper, the performances of two pier-supported footings and three isolated piers during compressive load tests were simulated using an axisymmetric finite element model and compared to experimental data. A hardening-soil constitutive model with parameters estimated from in situ and laboratory tests was used to characterize the constitutive behaviors of the pier material and the matrix soil. Pier groups were modeled as unit cells with the tributary area determined from the center-to-center spacing. Cavity expansion modeling was used to simulate the pier installation process. Verifications of the numerical model were carried out by comparing the numerical results with the data obtained from full-scale, instrumented load tests. Interpretation of the numerical results focused on the load-deformation behavior, group effect, stress concentration ratio, and the development of stresses in the matrix soil. The distributions of vertical stress underneath the pier-supported footings are also characterized.