Response Analysis of a Suction Pile Under the Influence of Mooring Tension

The thesis focuses on the numerical prediction of the ultimate capacity of suction piles in normally consolidated clay in the Gulf of Guinea. Suction piles can be subjected to horizontal, vertical or inclined load. Each load scenario affects the response of the pile and thus, the ultimate holding capacity of the suction pile. Soil with low permeability was simulated using Plaxis-3D and applied as pressure and friction on the pile. Suction pile aspect ratio is 4.5. The suction pile is modelled using Abaqus . The suction pile plate is 40mm thick. An 8 node quadratic shell element with a geometric seed size of 100mm is used. The suction pile was subjected to certain specified load until soil collapse occurs; the value of tension load on mooring line was recorded. The angle between the mooring line and the horizontal was varied for the simulation to determine the worst angle to cause soil collapse around the pile. The maximum horizontal force and maximum vertical force were deduced for each load case. The angle between the mooring line and the horizontal was 33.3o when a force of 15290kN caused the local soil collapse, for lateral load, the load that causes soil collapse was much larger ; 25261kN. The pullout capacity of the pile was tested by a purely vertical force and a much lesser force caused collapse. Hence, the point of load application has a great effect on the ultimate local soil resistance and pile capacity. The above result is enough to conclude that the point of application of load along the entire length of the suction caisson together with the angle at which it is applied plays a key role in determining the mode of failure of the soil body around the suction pile.