Bearing capacity of shallow foundations on Florida limestone: A study of single layer and rock-over-sand subsurface

This study investigated the bearing capacity of shallow foundations on Florida limestone using 3D finite element modeling (FEM) with a bilinear strength envelope based on rock formations and bulk dry unit weights. Most Florida limestones at shallow depths are highly porous and have a low density and strength, thereby resulting in a ductile stress-strain response and contractive volumetric behavior under service loads, both of which are not well characterized by conventional bearing capacity methodologies. In this study, a bilinear Mohr-Coulomb elastoplastic model with a non-associated flow rule (negative dilation angle) was integrated into a 3D FEM code from a series of laboratory triaxial strength test results. Numerical simulations were performed for different footing sizes, shapes, and embedment depths using homogeneous rock and rock-over-sand subsurface. Beginning with the numerical results from a strip footing on a homogeneous rock deposit, a bearing capacity equation was developed for bilinear strength conditions. Further, the width, shape, and embedment factors were developed, and a reduction factor was developed based on the rock layer thickness and moduli of rock and sand for the rock-over-sand condition often encountered in South Florida. The study concludes with a comparison between developed equations and conventional bearing capacity methodologies.