Numerical study on pull-out capacity of torpedo anchors in clay

This paper reports the results from dynamic finite-element analyses undertaken to provide insight into the behaviour of torpedo anchors during pullout in non-homogeneous clay. The results were validated against field data prior to undertaking a parametric study, exploring the relevant range of parameters in terms of installation effect, impact velocity, anchor geometry, padeye position, pullout angle. Installation method (e.g. quasi-static and dynamic installation) has shown significant influence on the vertical pullout capacity, but that influence reduced to marginal for lateral pullout. The inclined pullout capacity was dictated by the anchor weight and fully mobilised anchor-soil contact surface area and consequently the capacity increased with increasing the number of fins. Due to the lower weight and total surface area, the 45° (at the padeye) pullout capacity of the finless anchor was 29% of that of the considered four-fin anchor. The results showed that this percentage can be increased to 83% by shifting the padeye location of the finless anchor to 0·56 times the anchor shaft length from the top. Anchor capacity under inclined pullout loading was presented as failure envelopes expressed in terms of dimensionless vertical and horizontal components, which lied between the envelops developed for piles and embedded foundations.