Design of a novel drilled-and-grouted pile in sand for offshore oil&gas structures

• The paper describes the development of a novel type of drilled and grouted pile designed for the offshore structures.
• Preliminary field trials were carried out to verify the MIDOS pile installation procedure and load carrying performance.
• The installation process was validated with the pile installed to its target depth of 17 m with ease, in under 3 h.
• The performance of the MIDOS pile was shown to compare favorably with conventional design procedures.

New offshore oil and gas exploration has placed renewed emphasis on developing structures in relatively complex geological conditions. Due to the damaging nature of impact driving, traditional steel piles used to support jacket structures, are not ideally suited to specific soil types, such as carbonate sands. Drilled and grouted piles are commonly used to support structures in these soil conditions. This paper describes a novel drilled pile, which has been developed specifically to provide a cost effective installation process while maintaining the benefits of grouted piles. The installation process negates the need for temporary casing in weak soils and minimizes the number of offshore operations. In this paper, the installation methodology and post-installation performance of a large scale onshore field trial is described. The installation process was successfully demonstrated with a 1.9 m diameter test pile installed in fine sand to 17.7 m depth in under 3 h. The performance of the pile, as measured in a tension static load test, was shown to compare favorably with existing pile design methods.