Numerical Investigation of the Installation Process and the Bearing Capacity of Suction Bucket Foundations

Abstract

This paper was developed in cooperation between the TUHH and Overdick GmbH & Co. KG. The goal of the presented work is gaining further knowledge about the installation and bearing behavior of suction bucket foundations for fixed offshore platforms based on sand. Buckets are usually made of steel and consist of a cylinder and a lid at the top. They are installed into the sea floor by pumping water out of the buckets to create suction, which drives the bucket into the soil. Suction buckets do not require heavy hammer-equipment for construction like common piles. Thus the installation procedure is much faster and protects the environment significantly by avoiding noise emissions. Therefore, suction buckets are to be considered as a serious foundation alternative compared to steel piles. For this paper numerical investigations are performed with the finite analyses software ABAQUS. A total of five finite element models — three for the bearing and two for the installation — were created to carry out parametric studies, while using a hypoplastic constitutive model to describe the soil conditions. Therefore, the buckets diameter, embedded depth and the pore-ratio are to be investigated. In addition three different load conditions are applied in the bearing capacity tests: the maximum vertical load, the maximum horizontal load and the minimum vertical load. During the simulation of the installation procedure different pore ratios are tested and it is attempted to simulate an installation by water-extraction. Based on these numerical investigations it is possible to investigate known and currently more or less unknown phenomena of the bearing and the installation of suction buckets. Thus, a more detailed knowledge about the function of this kind of foundation is to be gained. In addition, the numerical studies are compared to the design-procedure according to API RP-2A-WSD and the DNV CN-30.4.