Offshore skirted foundations can be simulated as pre-embedded foundations, since disturbance during installation is limited to a small region around the skirts themselves. The bearing capacity of this type of foundation may be assessed using limit analysis, based on a rigid-plastic idealisation of the soil. However, recent results have shown a significant gap between lower and upper bound estimates of capacity as the skirt depth increases. It is therefore necessary to use techniques such as the finite element method to assess appropriate bearing capacity factors more precisely, and also to identify the transition from shallow to deep failure mechanisms. The soil is considered as normally consolidated clay with undrained shear strength increasing linearly with depth. Soil flow mechanisms have been studied for embedment ratios of up to 5 and the flow mechanisms in normally consolidated soil have been compared with those in homogeneous soil. It has been found that, with increasing embedment ratio, the soil flow mechanism will change from surface failure to a deep, cavity expansion mode and that this transition occurs at a higher embedment ratio in a normally consolidated soil (with significant strength gradient) than in homogeneous soil. Limit analysis can give a reasonable prediction at shallow embedments before this transition. However, at deeper embedments it is necessary to employ a large penetration analysis in order to arrive at a true limiting capacity. In this paper, the limit bearing capacity and transition depths are evaluated and compared with corresponding results for homogeneous soil.
|Pages (from-to)||71 - 77|
|Journal||Soils and Foundations|
|Publication status||Published - 2002|