Gathering the geotechnical data needed to determine foundational engineering parameters is a painstaking component of any wind project, and further complicated when that project is offshore. Marine geotechnical studies, which involve the physical sampling and testing of seabed soil to determine its characteristics, provide the information engineers need to develop foundation designs for wind turbines, cable, and other structures. These studies are based on analysis of data gathered from geophysical surveys and require significant experience with a range of marine-condition samples and test equipment.
Alpine Ocean Seismic Survey’s R/V Shearwater is a multiuse vessel equipped to deliver turnkey marine data acquisition services, including geophysical and geotechnical studies.
Alpine Ocean Seismic Survey, Inc., a subsidiary of U.K.-based Gardline Marine Sciences Ltd., recently added geotechnical capabilities to its existing marine data collection services for North American clients. Norwood, NJ-based Alpine Ocean, working in partnership with its sister company, Gardline Geosciences, is one of the few companies working in the U.S. capable of providing a turnkey geotechnical, geophysical, environmental, hydrographic, and oceanographic package, says President Robert Mecarini.
Gardline Geosciences has gained extensive experience conducting geophysical and geotechnical surveys for European offshore wind projects, while Alpine combines over 50 years experience performing geophysical surveys worldwide with a successful track record in site characterization studies for several prominent development-phase projects in the U.S. These include LeedCo in Lake Erie, Fishermen’s Energy projects in state and federal waters, and other projects along the East Coast. Developers of the Atlantic Wind Connection project, which will create a power transmission backbone stretching from Virginia to New York, have awarded Alpine a contract for first-phase survey efforts.
Offshore geophysical surveys provide a detailed image of surface and subsurface characteristics of the seafloor including bathymetry, hazards, potential areas of archaeological interest, geological structure, and other features, according to Mecarini. This data, along with geotechnical data, is required to determine cable burial routes as well as design turbine and other structure foundations. “We use a variety of acoustic equipment [sonar] to collect this information. Depending on the frequencies used, and the manner in which the frequencies are transmitted and received, we image different aspects of the seafloor and its substructure,” Mecarini says.
The geotechnical assessment that follows involves physical testing and sampling of the seabed. Researchers use a range of technologies to collect data, including conventional soil boring and cone penetration testing (CPT). Whereas soil boring requires sending samples to the laboratories for analysis, CPT units take in-situ measurements by pushing a probe into the soil that measures a variety of parameters such as soil density and shear strength.
“When CPTs can be used, usually in softer sediment types, they offer the most accurate and reliable way to measure seabed properties for engineering purposes,” says Andy Barwise, business development director of Gardline Geosciences. When soil samples are needed, Gardline and Alpine choose the appropriate tools from a range of sampling and drilling technologies based on project requirements, water depth, and drilling depth.
Scientists examine a sediment sample onboard the Shearwater. The sample reveals information about the ocean floor at the candidate wind-turbine site.
In shallower waters, says Mecarini, many projects use jack-up platforms with truck-mounted drilling rigs run by contractors whose experience lies in land-based operations. However, he adds, “As development efforts in the U.S. start to move to deeper water, the use of jack-ups with truck-mounted rigs gets complicated, as these vessels are limited by water depth and this drilling approach isn’t designed for tougher marine conditions.”
To handle sampling and drilling in deeper waters, heave compensated drill rigs—devices that let a ship rise and fall with ocean swells while keeping drill rods properly engaged—address the safety and efficiency issues raised by jack-ups. These units can be permanently installed on geotechnical survey vessels or mounted on third-party barges and vessels, an important attribute for contractors who want to hire local providers to better engage the community in projects.
Although the U.S. has the largest onshore wind power capacity in the world, offshore wind development has lagged far behind Europe, and to a lesser extent, China. One contributing factor to the faster adoption of offshore wind in Europe is its relative lack of undeveloped land onshore, while the U.S. has ample land for turbines, says Barwise.
However, the issue with U.S. onshore wind production to date, Mecarini says, is that much of the development isn’t near high electricity demand centers. “One of the reasons you’re seeing wind farm development along the East Coast is because it has strong offshore wind resources and a high population density, making it a good place for the U.S. to site projects,” he says.
Both agree that for the U.S. offshore wind industry to move forward, the nation needs a long-term energy policy that provides a roadmap and stable incentives. “Right now incentives are uneven and unpredictable, and fossil fuels like gas and coal are relatively cheap,” Mecarini says. “Therefore, the economics of an offshore wind farm are not always appealing to an investor.” Still, there is a lot of positive thinking, he adds, but whether there will be a commercial-scale wind farm in U.S. waters within the next couple of years remains to be seen.
“I think it will ultimately depend on our politicians and their commitment to putting policies and incentives in place that will nurture this nascent industry,” he says. “If they don’t, we will be losing a great opportunity to create thousands of jobs, increase our energy independence while creating a hedge against fluctuating fossil fuel prices, and improve our environment. We will also be losing out to Europe and China on an opportunity to do what the U.S. has historically done best—pioneering the development of new technologies that pave the way for future economic growth.” WPE
Filed Under: Offshore wind, Projects
