A unique type of soil is found along the Atlantic Outer Continental Shelf. It is called greensand, named for its typically green to sometimes black color. The geological name is glauconite, the clay mineral that makes up the majority of the its structure. Historically, glauconitic ‘sand’ was mined for agricultural purposes due to its potassium content; several of these now-abandoned mines dot the New Jersey landscape across the coastal plain. More recent interest in glauconitic sand has arisen as offshore wind developers seek to build large fixed seafloor foundations to support turbines for generating renewable electricity.

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​The uniqueness of glauconitic sands relates to the fact that is not technically sand, but rather an agglomerate in pellet form, comprised of clay minerals bound to a granular substrate. It forms at the soil-water interface of the seafloor under low oxygen and low energy environments to mature into a soil high in iron and potassium. Its iron content at full maturity, typically over a couple of millions years, can reach about 30%, making the soil magnetic. During this maturation process, the particles undergo a recrystallization that creates fractures and fissures, weakening the particle. Its friability, or susceptibility to crushing, can be higher than many carbonate soils which are notorious for creating construction and engineering challenges in both onshore and offshore environments.

The crushing of glauconitic sands changes its behavior of the soil from coarse-grained (i.e. well-drained, frictional) to fine-grained (poorly drained, cohesive). This fundamentally alters the engineering response of the soil, affecting foundation design. For large offshore monopile foundations, the main design aspects comprise installation, long term axial capacity, and lateral pile-soil stiffness. The monopiles first have to get into the ground, and this requires high capacity offshore pile driving equipment, essentially massive hammers that bang the piles into the seabed. With high frictional resistance from the native sand at the pile tip together with the high cohesive resistance from the crushed sand along the pile shaft, it can be difficult to ensure the piles can be driven to their target depth. Mitigations to alleviate the high shaft resistance, such as external driving shoes, can impact the long term axial capacity and lateral pile-soil stiffness.

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​To address these concerns, two major offshore wind developers have launched a joint industry project to investigate piling in glauconitic sands (PIGS, for short). The project is led by the Norwegian Geotechnical Institute and supported by several universities, consultants and contractors. A test site located within the glauconitic sand belt of New Jersey has been selected for field work, comprising geological and geotechnical investigation, pile installation, and axial and lateral pile load testing. The University of Massachusetts Amherst has been awarded an initial grant for 120,000 USD to play a key role in the technical leadership of the project, providing field testing support and performing advanced geotechnical laboratory testing. With the Phase 2 field work now wrapping up, the UMass team, led by Associate Professor Zack Westgate of the Civil and Environmental Engineering Department, look forward to kicking off the third phase of the project this summer with advanced laboratory testing using the geotechnical facilities on campus.

Dr. Zack Westgate is an Associate Professor of Civil Engineering at the University of Massachusetts, Amherst. He received his doctorate from the University of Western Australia, and his master's degree from UMass Amherst, both in geotechnical engineering. Zack has over 15 years' experience as a consulting engineer and manager for multidisciplinary design firms, geotechnical contractors, and specialist consultancies in the marine energy industry, and is currently a consultant at the Norwegian Geotechnical Institute. His experience and research interests include offshore geotechnics, foundation engineering, pipeline/riser/cable-seabed interaction, experimental methods, and soil-interface mechanics. He currently teaches undergraduate and graduate courses on foundation engineering and offshore geotechnics. He is an active member of both the SUT OSIG and MRE committees and serves on ISSMGE and API/ISO technical committees related to offshore foundations and pipeline/riser standards development. He is a registered Professional Engineer in several states.