Modelling the installation of suction Caisson foundations in sand

Suction caisson foundations have been widely used in the offshore oil industry and the current trend is to extend their use to offshore wind farms. The caisson consists of a large hollow cylindrical structure usually made from steel, open at the base and closed at the top.
The installation procedure of suction caissons must be analysed carefully to predict adequate control of the applied suction and prevent caisson damage due to critical conditions such as buckling and piping etc. The installation analysis is also useful as a preliminary step to obtain initial soil conditions for a bearing capacity analysis of the caisson foundation.
This paper presents the results of finite element simulations of suction caisson installation in sand. A two dimensional axisymmetric model is built using the ABAQUS commercial package and used in the prediction of soil conditions that develop during caisson installation. The required suction control is predicted by monitoring the increase of soil resistance as the caisson is pushed into the seabed. For this end, the water saturated soil is described as a two-phase porous medium, and the caisson is modelled by solid elements. A frictional contact algorithm based on a slide-line formulation is used in order to describe the interaction between the caisson and the surrounding soil. Contact constraints such as non-interpenetration between caisson and soil and impervious caisson surface, are enforced using a Penalty procedure. An interface is also created in the soil to facilitate soil flow around the caisson tip during caisson penetration. Such an interface is free to deform during caisson movement, without imposing any constraint on the penetration path, apart from enforcing continuous stress and pressure prior to soil separation. The present numerical model is adopted to estimate soil resistance to caisson penetration and emphasise the role of water seepage induced by suction in sand.