ABSTRACT
The capacity of foundations under combinations of vertical and horizontal (i.e.V-H) loading has been studied for a range of soil conditions. There are two main design approaches: (i) the Terzaghi bearing capacity method, and (ii) the failure envelope approach. In the bearing capacity method, modification factors for load inclination are applied to the vertical bearing capacity equations as first suggested by Terzaghi (1943). More recently, use of the failure envelope method has become more common. In this method, the load components (V, H and M) applied to the foundation are plotted on an interaction diagram and an envelope of failure states is ascertained (e.g. Zaharescu, 1961; Georgiadis, 1985; Nova & Montrassio, 1991; Gottardi & Butterfield, 1993). Equations describing failure envelopes have been presented by a range of authors for different soil conditions (e.g. sand, clay.) and foundation types (e.g. plan shapes, embedment ratios etc.). It should be noted that the majority of equations for drained conditions (e.g. Nova & Montrassio, 1991; Gottardi & Butterfield, 1993) have been for flat plate foundations resting on the soil surface.
