With support from the Norwegian Deepwater Programme - Seabed Project NGI developed criteria for design of a new deepwater seabed sampler. The aims of the design was to have a sampler that can penetrate 15 - 20 m below seabed in 2000 m, with at least 95 % recovery and sample quality similar to what can be obtained with a thin wall piston sampler in drilling mode. The design criteria were followed up by more detailed studies at NGI, including laboratory tests and field and FE studies. The Dutch manufacturer APvandenBerg also joined the project and made detailed design of important features like a stationary piston and core retainer as well as instrumentation. A prototype was made and GardlineLankelma joined the project to take care of handling aspects of the sampler. The sampler was tested out at NGI's onshore test site at Onsøy and was subsequently used twice at the Troll field as part of soil investigations for Statoil. Results of the laboratory tests carried out on the obtained samples confirm high quality.
For many offshore geotechnical problems, e.g. anchoring of floating structures with suction piles, or evaluation of submarine slope stability, it is sufficient to determine soil conditions to a depth of say 20 - 40 m below seabed. It is also important to get a comprehensive understanding of the geology of the shallow sediments for most field developments. A cost efficient way of collecting soil data is to carry out seabed sampling to about 20 m below seabed and to perform seabed piezocone (CPTU) tests to somewhat deeper depths, e.g. 40 m. However, it is of vital importance that the quality of the samples is good from a geotechnical viewpoint, otherwise the results of laboratory tests on the samples will not be representative for the in situ conditions. Standard Kullenberg piston samples have significant problems both with recovery and sample quality (eg. Lunne and Long, 2006).
The aim of the new sampler project, as described in this paper, was to design a sampler that can penetrate 15 - 20 m below seabed in 2000 m, with at least 95 % recovery and sample quality similar to what can be obtained with a thin wall piston sampler in drilling mode.
The initial part of the project consisted of a comprehensive review of which aspects of seabed sampling are most important with respect to sample recovery and sample quality. The review consisted of a thorough literature survey, a study of findings in recent NGI research and consulting projects and communication with colleagues in other organizations. The outcome of this study was establishment of a set of design criteria (NGI, 2002 and Lunne and Long, 2006) and identification of some aspects of sampler design that needed to be studied by experimental and theoretical work (NGI, 2004). The last part of the project consisted of the final design of the sampler, and subsequent onshore and offshore testing (NGI, 2006).
The project was financed by the Norwegian Deepwater Programme - Seabed Project, a research programme aimed at preparing for field developments in the deepwater Norwegian Sea and financed by awarded licence holders.