Failure mechanisms of skirted foundations in uplift and compression

Kinematic soil failure mechanisms around skirted foundations, embedded in lightly overconsolidated clay and subjected to undrained compression and tension, have been investigated through digital image analysis of drum centrifuge tests and compared with predictions from finite-element analyses. Analysis of images captured in the centrifuge tests showed that rather different kinematic mechanisms govern failure in tension and compression. In tension, a reverse end bearing mechanism involving a bulb of soil beneath the foundation was mobilised even for a skirt depth to foundation diameter ratio as low as 0·1. Bearing capacity factors from centrifuge tests for a selected embedment ratio were similar in compression and uplift despite the difference in associated failure mechanism. Comparison of the failure mechanisms observed in the centrifuge tests with those predicted by finite-element analyses shows some marked differences, in spite of close agreement of bearing capacity factors.