The paper describes the main features and initial underwater field-testing results of a remotely operated submersible drill rig designed to obtain continuous cores of soil and/or rock up to 6m long in water depths of 200m. The rig mast angle is hydraulically actuated covering 90° of altitude. This enables both a fully horizontal position used for deployment onto, and recovery of the rig from, the seabed, as well as a fully vertical position during coring. The frame is equipped with positioning and inclination sensors for accurate register of core orientation. Coring equipment with diameter of up to 133mm can be mounted in the rig, thus enabling the recovery of relatively large-diameter cores. The coring operation is fully instrumented and all the drill operation parameters such as torque, thrust, advance, injection rate and pressure are recorded. The equipment is deployable from a variety of platforms.
The need for marine geotechnical soil investigations is clearly increasing. Apart from the already seasoned drivers of this industry (e.g. harbour and coastal developments), or the unrelenting trend towards underwater resource exploitation by the extractive industries, development of marine renewable energy resources, particularly for wind, is quickly approaching maturity. The costs associated with their deployment and mobilisation are usually the main item in any marine soil investigation campaign (Gourvenec and Randolph, 2011), and the choice of which type of vessel/platform to use requires careful consideration. Obviously important amongst the factors that need to be considered are the required investigation depth, the water depth at the site and the expected nature of the soils under investigation. Perhaps even more essential factors to establish are the quality level of the data and the ability of the vessel to deploy the necessary equipment and, therefore, the nature of that equipment.