ABSTRACT
Bucket foundations are one of the foundation technologies used in the construction of offshore oil and gas platforms as illustrated in Figure 14.1. The technology is especially suitable for shallow water areas where there are thick sediment layers on the sea floor. The bucket foundation platform has high stability, mobility and re-usability while its relatively simple structure saves construction materials and costs. It is installed by using negative pressure suction methods, which reduce the on-site construction
times. The installation process minimally disturbs the marine environment and is thus an environment-friendly technology, widely used since the early 1990s (Baerheim 1995; Erbich et al. 1995; Rusaas 1995; Tjelta 1995a, 1995b). During platform installation, a key technology is how to press a bucket foundation efficiently so that it penetrates the sea floor’s sediment layers. In this process, water pumps are used to produce a negative pressure inside the bottom-up bucket. As a result, the relatively high pressure of the sea water and the atmosphere outside the bucket forces interstitial water in the surrounding sediment to flow into the bucket. This water flow forms a seepage field in the sea-floor sediments both outside and inside the bucket. Field operations show that this seepage field can cause favorable and unfavorable effects on the suction penetration of the bucket foundation. For instance, the penetration resistance with seepage can be reduced to half of that without seepage. On the other hand, the increase in effective stress between the surrounding sediment and the bucket wall may hinder penetration. Therefore, it is important to analyze the dynamics of the seepage field during the penetration process to increase the successful installation of the bucket foundation platform.
