Theoretical Study Of The Failure Mode And Pullout Capacity Of Suction Anchors In Clay

As the demand on energy rapidly increases, oil companies extend their search foroil and gas into deep and ultra deep waters. Because of good performances both inpullout capacity and deepwater installation, suction anchors are widely applied inmooring systems. Previously published methods for predicting the inclined pulloutcapacity of suction anchors are mainly based on experimental data or FEM analysis.The present study aims at developing a rational and simple theoretical analysismethod which can be used to simulate the failure modes and pullout capacity ofsuction anchors in clay.In the present work, the author introduces a rational mechanical model forsuction anchors with limit equilibrium theory and a principle that suction anchor willfail along the direction that requires the minimum mooring force. By applying themechanical model and the principle, an analytical method is developed to predict thefailure mode and ultimate pullout capacity of suction anchors.A parametric analysis is performed systematically to study the effects of soilproperties and the geometry of suction anchors. In order to examine the analyticalmodel, the failure angle and pullout capacity of suction anchors from FEM simulation,numerical solution and laboratory tests in uniform and linear cohesive soils areemployed to compare with the theoretical predictions and the agreement is satisfactory.An analytical method that can evaluate the optimal position of the attachment point isalso proposed in the present study. When the mooring force is attached on theoptimum attachment point, the suction anchor has the largest pullout capacity.