Analysis of shallow footings for relatively simple loading configurations and geometries is generally performed through the application of conventional bearing capacity calculations. These calculations are essentially based on adapting theoretical solutions for the vertically loaded infinite strip problem through the application of bearing capacity factors to other cases, such as footings of finite dimensions (rectangular or circular), sloping ground, inclined bases and combinations of vertical, horizontal and moment loadings. This approach has proved very successful and, from a designer's point of view, is very attractive since the process is straightforward to apply, provided suitable bearing capacity factors are available.
This paper presents the results of a study of the response of triangular footings subjected to both centric and eccentric loading. A series of small-scale single gravity tests were carried out on model footings to investigate the footing response. In addition, a basic numerical study was carried out using a simple elastic-perfectly plastic soil model.
The model tests are analysed using conventional bearing capacity theory in conjunction with the derivation of an ‘equivalent’ rectangle, which has section and areal properties derived from the reduced area of the loaded footing.
Shallow foundations used in the offshore environment are invariably subjected to complex loading patterns, where the application of conventional bearing capacity theory through the use of bearing capacity factors is limited. Consequently much research has been directed to the analysis of shallow foundation systems through the use of both physical and numerical modeling techniques1, 2, 3. In most cases this research has focused on regular shaped footings - rectangular and circular - and little work is reported for the case of irregular shaped footings, in particular, triangular ones. Such shapes are often encountered in the form of ‘mudmats’ used for the temporary support of offshore structures prior to the installation of piles. In some instances, irregular shaped foundation pads are also used for the permanent support of more minor structures, such as sub-sea isolation valves (SSIVs). The actual shape of the foundation pad, or mudmat, is usually dictated by the geometry of the structure, i.e. triangular mudmats are often formed when steel plates are welded between the bottom chords of an offshore jacket structure.
The bearing capacity of shallow foundations has received much attention in the study of soil mechanics, and as a result several approaches to the problem have been formulated4, 5, 8, 9. These bearing capacity formulae are generally applicable as variations in geometry, and loading are catered for through the use of bearing capacity factors. For most conventional foundations (square, rectangular and circular) these factors are generally satisfactory, however, it is not obvious how best to apply this approach to irregular footing shapes.
Triangular footings, for example, are regularly used for the temporary support of offshore structures in the form of mudmats formed at the apex of jacket legs (Figure 1). There is little guidance in the literature to aid the analysis of irregular shaped footings, and current practice follows the recommendation that the effective area of irregular shapes