Effects of long-term pre-loading on the performance of a footing on clay

An instrumented footing test in Bothkennar clay is described, which examines the effects of a long period of drained pre-loading on the footing's undrained bearing capacity. It is seen that pre-loading induced a significant increase in the subsequent foundation stiffness due to consolidation but also due to creep and ageing processes that led to an outward expansion of the clay's large-strain yield surface. Pre-loading also resulted in a downward shift of the bearing capacity mechanism and an ultimate bearing capacity that was substantially greater than that expected due to consolidation effects alone. Evolving anisotropy and creep are identified as being important contributory factors to the enhanced undrained capacity after pre-loading.