Reliability-based ultimate limit state design of spread footings on aggregate-pier-reinforced clay

This paper summarises the evaluation of previously existing and recently developed bearing capacity estimation methods for spread footings resting on aggregate pier reinforced clay. A load test database of full-scale footings resting on stone columns was used to generate an accurate ultimate limit state design model for bearing capacity and characterise the associated model uncertainty. Different levels of variability in area replacement ratio, slenderness ratio, length of pier, depth of footing embedment, and undrained shear strength, were incorporated in the resistance factor calibration in order to account for possible uncertainty in the load test database and future construction. Resistance factors were calibrated as a function of the ratio of dead to live load, reliability index, and total variability in the nominal bearing capacity. The operational factor of safety was computed for comparison to allowable stress design procedures and indicated that typical factors of safety associated with current practices can continue to be used for soil deposits with moderate variability.