Theoretical studies on penetration resistance of a modified suction caisson in sand

Abstract

The modified suction caisson (MSC) is an innovative offshore foundation, consisting of an internal caisson (IC) and an external skirt (ES). Determining the penetration resistances is a key point to predict the required suction for installing MSCs smoothly in sand. During suction-assisted installation of MSCs, the seepage will greatly change the effective streess in sand, and thus affect the penetration resistance along the caisson wall. Therefore, this study clarifies the distribution characteristics of the seepage field by exploring the excess porewater pressure and hydraulic gradient inside and outside the MSC with different aspect ratios in sand with SEEP/W. Meanwhile, the water fluxes are also investigated. It is found that the minimum absolute values of the excess porewater pressures and the hydraulic gradients outside the IC appear at the “0 seepage line”. The absolute values of water flux reaches the maximum at the tip of the IC and the ranges of the negative water fluxes outside will enlarge with increasing the aspect ratio. Based on the above results, the method of calculating the MSC penetration resistance and the formula of calculating the required suction for the MSC installation in sand is proposed, which is verified by the model test results.