Experimental Study on Gravity Anchor for Optimum Design of Shear Key

Abstract

The purpose of a gravity anchor is to moor the installation barge affected by the environmental condition during installation at the offshore site. It is important to obtain the sufficient holding capacity to prevent the anchor from dragging. There are several methods to enhance the holding capacity such as increasing its self-weight or attaching the shear key at the bottom of the gravity anchor. However, increasing the self-weight of gravity anchor is a constrained approach due to the limitation of handling equipment capacity. Therefore, it is necessary that the shear key design should be optimized to maximize the holding capacity under limited handling equipment. In this paper, reduced scale model tests simulating rock condition mixed by sand, cement, and water are performed. The actual offshore mooring condition is simulated by using towing carriage. Five types of gravity anchor models which have different shear keys are assessed to examine what type of the shear key is the optimum design. The optimum shape and the number of shear keys for maximizing the holding capacity are assessed through this study. The results of this study can be utilized to design the shear key of gravity anchor.