Stability of installation of marine caisson anchors in clay

Abstract

If they can be installed, steel caissons offer a number of advantages over more traditional marine anchors in the exploitation of offshore resources. The stability of insertion of such caissons into clay has been studied both theoretically and experimentally. A relatively simple theory is presented, which shows that directional stability depends primarily upon the method of insertion, gravity loading (self-weight or load imposed on top of the caisson) being much more likely to result in instability than suction (pumping out water from inside the caisson). The relative dimensions of the caisson and soil stiffness are also taken into account, and both plain circular and internally stiffened caissons are considered. A brief account is given of some model tests that have been carried out, at two different scales, which give substantial support to the theory, at least within a certain range of soil stiffness. Although in principle suction appears to be a very good way of inserting caisson anchors, its use in practice may involve certain difficulties. Keywords: caissons, soil-structure interaction, stability, anchors, offshore structures, clay.