Pullout behavior of superpile anchors in soft clay under static loading

Abstract

For anchoring tension leg platforms (TLPs) to the seabed, several new anchoring systems are being developed. The superpile anchoring system is one such new system. This article presents the results of laboratory tests to investigate the suitability of superpile anchors as foundations of TLPs in soft clays. The pullout load‐displacement behavior under static loading of model superpiles embedded in soft clay was studied and compared with that of similar large‐diameter piles having open tops. Under static loading, superpiles do not show any distinct failure and the pullout load continues to increase with displacement up to as much as 60% of the superpile diameter. The soil plug moves up with the superpile. Significant resistance is developed beneath superpiles during static pullout. This resistance (though of a short‐term nature) gives added uplift capacity and prevents sudden failure as observed in the case of large‐diameter piles having open tops. This resistance can be expressed in a dimensionless form as bottom breakout factors. The bottom breakout factors are strongly dependent on the pullout rate. They vary marginally with the embedment ratio and appear to be independent of the water content of soil