Experimental study of uplift resistance of shallow skirted foundations in clay under transient and sustained concentric loading

Wind, wave and current forces cause significant overturning loads to be transmitted to foundation systems of fixed-bottom offshore structures, while buoyancy forces, in conjunction with environmental loading, impart direct tensile loads to foundations of floating facilities. Shallow skirted foundations are a potentially attractive foundation solution when overturning or tension loading is significant, as suctions mobilised within the soil plug provide tensile resistance. While passive suctions are maintained, undrained reverse end bearing will govern failure providing enhanced uplift resistance compared with vented pull-out of the foundation unit (with or without the soil plug), governed by skirt/soil friction. Currently uncertainty exists over the limiting ratio of skirt depth to foundation diameter to mobilise undrained reverse end bearing and the duration over which passive suctions can be sustained. This paper reports results from beam centrifuge tests investigating the response of shallow skirted foundations in lightly over-consolidated clay to concentric transient and sustained uplift.