Sea Technology

JAN 2013

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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T1 and T2 are the arbitrary time boundaries of the sound event (i.e., the pile driving blow), and T0 is 1 second. Normally, the sound event between T1 and T2 is about 0.05 to 0.40 seconds. Reference sound pressure p0 is 1 micropascal. Essentially, the SEL The Dive Drill works by drilling out of the complete feed while using equation includes the clamping systems located in the up- square of the observed time-variable sound per and lower positions. pressure p(t), takes the average over time T1 and T2, and divides by the squared reference sound pressure p02 (energy averaging). It is important to point out that the driving noise depends not only on the intensity of the pile ramming but also on the averaging time and the pause between the pile driving blows. The single-event level of a sound pulse (pile driving blow) is therefore the level of a continuous sound of 1-second duration and same sound energy as the impulse. Different measurements during pile driving of research platforms and foundation structures of offshore wind turbines in the North Sea and Baltic Sea give SEL values of 10 decibels higher than the 160-decibel limit. Therefore, BAUER Maschinen is developing drilling systems for alternative offshore pile installations. BSD 3000 Drilling Tool In the case of the successful installation of a 1-megawatt tidal energy turbine in the European Marine Energy Centre test area off the island of Eday in Orkney, Scotland, in July 2011, a monopile was chosen as the foundation structure due to the large loads. At a water depth of about 33 meters, the seafoor consisted of sedimentary rocks from the Silurian and Carboniferous periods that were generally sandstone and siltstone of medium strength (up to 150 micropascals) in alternating strata. The turbine axis was located about 15 meters above the seafoor. The rotor blades had a diameter of 16 meters. The monopile's pipes had a 2-meter outer diameter with 60-to90-millimeter wall thickness. A transition piece was welded at the pile tip. The connection with the rock strata was 11 meters long and had a diameter of 2.3 meters. The monopile was installed by means of BAUER Maschinen's BSD 3000 drilling tool. The drilling rig consists of three main components: drilling template with legs, including leveling and weight plates, and the middle piece, including tubing clamp and clamp; a guide tube with casing shoe and internal consoles, and bars for supporting the drilling unit; and the drilling unit with a rotary drive, rag and pinion, drill pipe and the roller bit drilling head. The drilling was performed with a conventional rotary drill with a full-face roller bit with heavy weights. Drill cuttings were transported by airlift. The air siphon tube ended just above the drill. The drilling took about 24 hours, and the drill pressure had to be adjusted continually due to the varying rock ground conditions. Once the drilling operation was completed, the pile was threaded into the guide tube with an adapter at the pile tip. The pressing operation involved about 40 tons special grout and lasted 50 minutes. To control the grouting progress, fber-optic cables were fxed on the outside of the monopile to provide information on the grout's propagation and hydration. Dive Drill and Alternative Pile Installation Methods As its BSD 3000 drill is not suitable for offshore drilling operation in soils, BAUER Maschinen has developed the Dive Drill for offshore foundation construction in hard to soft soils. The Dive Drill, presently in development, could be used for drilling a small borehole (about 3 meters) and is therefore suitable for small-diameter monopiles or for tripod or quadropod foundations. The Dive Drill weighs approximately 35 tons. The rotary drive produces a torque of 275 The drilling tool and delivery tube of the Dive Drill for soft soils. 48 st / JANUARY 2013 www.sea-technology.com

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