ON THE BEARING CAPACITY OF SURFACE FOOTINGS ON SAND UNDER GENERAL PLANAR LOADS

Abstract

Estimation of the bearing capacity of a shallow footing subjected to both inclined and eccentric loads is usually based on well-known limit-equilibrium solutions which apply linear superposition to a problem that is highly non-linear. This paper concerns an alternative approach using "interaction diagrams" to relate the different loading components at failure. Such curves define a region inside which all allowable load combinations must lie. They can be obtained experimentally as the failure envelope of a series of load tests. A comprehensive experimental programme, using a new three-dimensional, small-scale physical model, has been carried out at the University of Padua to determine the form of such diagrams for a very dense sand. The experimental rig as well as the test programme-in which the loading path was the only variable parameter-is briefly described. Failure conditions in all three loading component planes are analysed and very simple expressions are found to interpret the experimental data in an acceptable way. In the H-M/B plane, where the sign of the eccentricity is important in relation to the direction of the horizontal load, a new, interesting geometrical form of failure envelope has been revealed. All the planar interaction diagrams investigated appear to be load-path independent and therefore provide a rational way of studying the load capacity of such footings.