This paper describes the design and installation of twelve large capacity suction anchor piles in the North Sea. Innovative both in concept and design, these piles were the first commercial application of the suction pile principle and its success proves that the suction on pi 1e is an attractive solution for anchoring mooring buoys. As the installation does not require any driving or drilling operation from large, conventionally moored barges but only 1ight craft, the suction pile is likely to find application as removable anchor points for various systems (CALM, SALM, Supply Vessel Moorings, etc???..) in water of any depth.
The paper focuses on the specific problems of the first application starting from acquisition and analysis of soil data through development of new geotechnical and structural design techniques to installation and testing. None of this material has previously been published and problem areas of general interest are highlighted. Several of these problem areas were the subjects of special laboratory and theoretical investigations for which the principal conclusions are outlined. Results of measurements taken during installation and subsequent testing are given and compared to theoretical results obtained at the design stage.
Details concerning the installation phase, including equipment and duration, are given so that potential users will be able to estimate the substantial savings on surface vessels that this novel installation concept offers.
Two Catenary Anchor Leg Moorings(CALM) were ordered at the end of 1979 by Dansk Boreselskab A/S (DANBOR) for the Gorm Field in the Danish sector of the North Sea (see location map on figure 1) and installed in the summer of 1980. These two buoys were designed for crude loading and in the future for condensate loading. Once installed, the buoys were connected to a process platform by a 12-inch diameter submarine pipeline. The process platform is connected to two wellhead platforms and to another platform in the neighboring DAN field. The two buoys must then transfer the oil production of both the GORM and DAN fields. Initially, 35,000 dwt tankers will be employed but the berth can accommodate up to 70,000 dwt tankers.
One CALM and 12 anchor points were designed and delivered by Single Buoy Moorings Inc. to meet the specific requirements and environmental conditions. A maximum design chain force of 200 tones was considered acting horizontally at mud line, resulting in a design of six anchor chains of 3 /4 inches for each CALM. Each chain leg is connected to the seabed by means of a suction emplaced anchor pile (called "suction pile", hereafter for brevity). A total of twelve suction piles were designed by SBM Inc., the 1icensee for these suction piles developed by Shell International Petroleum Maatschappij B.V. (SIPM).
The water depth on the site is approximately 40 meters. The soil conditions, which are described in detail in Section 2, primarily consist of a 6 m sand layer underlain by 1 to 2 m of soft clay then by stiff clay.
