ABSTRACT
Following the world demand for clean energy, the development of Offshore Windfarms (OWF) has been in constant growth with more challenging sites being considered for the construction of these OWF. Three Offshore Substations (OSS) of three different OWF located off the North and West coast of France, are installed on four-legged jackets founded on piles. For each of the OSS, the installation method of the pile foundations was different due to the soil conditions found on site: Rock Socket Drilling (RSD), Drill and Grouted (DG) and Drive-Drill-Drive (DDD). For all the three OSSs a pre-pilling template was deployed on the seabed. For the RSD method, for each pile a casing was oscillated into the seabed. Afterwards the rock socket was drilled to target depth and the casing retrieved after grouting. Then the pile was installed in the socket and the annulus between the pile and socket was grouted. For the DG method, first a pile was driven to the shallowest hard layer. Next a socket was drilled to target depth and the pile inserted. Afterwards, the inserted pile was grouted in the socket and in the driven pile. For the DDD method, first the pile was driven until initial refusal. Then a pilot hole was drilled and afterwards the pile was driven to target depth. In this paper, a more detailed description and challenges of these installation methods are discussed.
