ABSTRACT
Intermediate foundations may encounter a range of hazards and are arguably more hazard prone than either shallow or deep (pile) foundations. To avoid on-site embarrassment during installation in weak clays, current design practice is to use reasonable wall thickness to diameter, WT/D, ratios, and to vary thickness with depth (i.e. highest WT near the top, to accommodate highest underpressures and, if possible, avoid using internal ring stiffeners). In addition, if they are present, internal stiffener outstand widths are kept as small as possible and are also chamfered. Finally, a reduced internal soil-wall adhesion or friction factor, ai value, is considered above the stiffener to assess (Low, Best and High Estimate) penetration resistances and corresponding underpressures. Subject to economic and time constraints, intermediate foundation sites should be investigated as comprehensively as possible.
