Abstract

The geotechnical behavior of shell foundations was investigated experimentally, numerically, and theoretically. Experimental investigation was carried out on nine prototype foundation models in loose, medium, and dense sands. Experimental set-up was organized and instrumented to perform the testing program. Loading tests were conducted on surface as well as embedded footings. Triangular, conical, and pyramidal shell models were tested against conventional strip, circular, and square flat counterparts, respectively. The influences of shell configuration on the ultimate bearing capacity, settlement, contact pressure distribution, and stresses within the soil mass, were investigated. Special loading tests using colored sand layers in a Plexiglas tank were performed to determine the failure mechanism of shell foundations. Numerical modelling, using the finite element code "CRISP," was conducted to simulate the experimental tests conditions of the plane strain models. Elastic perfectly plastic soil model, employing Mohr-Coulomb's yield criteria, was adopted to simulate the behavior of the tested sand. Deformed meshes, displacement vectors, stresses, strains, and displacements of the plane strain models are analyzed and presented. A theoretical model to predict the ultimate bearing capacity of shell foundations was developed. The theory provides kinematically and statically admissible solution. The effects of shell configuration on the shape of rupture surface and accordingly on the ultimate bearing capacity were incorporated. A computer program "BC-Shell" was developed to perform the mathematical calculations of the theoretical analysis. The program "BC-Shell" was then designed in an interactive mode for an easy application to predict the ultimate bearing capacity. Parametric study was conducted to examine the sensitivity of the governing parameters on the ultimate bearing capacity. Design charts and design tables are also presented to determine the bearing capacity coefficients and depth factors. In addition, the theory was extended to predict the ultimate bearing capacity of shell foundations in axisymmetrical and three dimensional conditions by introducing shape factors for shell foundations. The results of this study support that shell foundations should come into wider use in the geotechnical field as a serious alternative to shallow and deep foundations.