PIGS - Piling in Glauconitic Sand Joint Industry Project (JIP)

PIGS was established in August 2021 to conduct site investigation, field-scale pile testing, and data interpretation related to pile drivability and static vertical and lateral load testing. The main goal of the JIP is to develop an understanding of glauconitic soil behavior related to site characterization and soil-structure interaction to develop a framework for assessing the impact of glauconite on offshore wind infrastructure development, with a particular focus on the US Atlantic OCS and pile foundations.

Five industry developers have financed the JIP to date, comprising Equinor, Ørsted, Avangrid, Attentive Energy, and RWE. NGI is leading the project, with technical oversight and advisement provided by the University of Massachusetts Amherst and an advisory panel of industry experts.

Scope of Work

The JIP scope of work has focused on a single test site to date and is divided into three main phases, as listed below and detailed in the Project Phases section. A fourth phase is currently being planned. Its execution is subject to the necessary infusion of additional industry funds.

• Phase 1: site search and selection
• Phase 2: Field investigation, pile installation, and load testing
  - Site characterization activities at the test site
  - Pile installation and load testing
• Phase 3: Laboratory testing and data integration, with seven work packages

Glauconite Sands – a new offshore challenge

Offshore wind development in the US is expanding rapidly, with 30 GW of energy planned for development by 2030. Much of this development is focused on the North Atlantic and Mid-Atlantic Outer Continental Shelf (OCS), primarily due to its proximity to high energy demand, shallow water depths suitable for fixed-bottom foundations, and strong wind speeds.

The foundation types constructed to date, or now in the design stage, are primarily deep foundations consisting of jacket piles or monopiles. The Bureau of Ocean Energy Management (BOEM) designated the Atlantic OCS as a “frontier” region since there is limited experience with the geology and geotechnical properties and behavior of seabed sediments for design purposes. Multiple challenges have emerged, including high spatial variability and the presence of boulders, calcareous sediments, and glauconite sands.

The Atlantic Outer Continental Shelf (OCS) features glauconite-rich sediments, impacting pile installation for offshore development. Glauconite transforms from sand to fine-grained soil upon shearing, causing uncertainties in piezocone penetration tests (CPTu). Pile driving induces a shear zone of crushed glauconite around the shaft, affecting shaft friction and impeding target penetration depths.

Crushed glauconite, observed under static and dynamic conditions, leads to high soil resistance to driving (SRD). Coarse-grained glauconite at the pile tip and degraded fine-grained glauconite along the shaft contribute to elevated SRD. Areas with negative pore pressure offshore intensify effective stresses during driving, potentially causing high resistance and pile refusal. Predicting blowcounts using programs like GRLWEAP faces challenges due to uncertainties in quake and damping parameters. Previous projects highlight lower-than-predicted blowcounts, complicating empirical SRD models. Limited experience with glauconite conditions introduces significant uncertainty in pile-driving predictions for jacket piles and monopiles.

To address the uncertainties of glauconitic sand behavior around piles, a Joint Industry Project (JIP), Piling in Glauconitic Sand (PIGS), was established in August 2021

Geological and Geotechnical Characteristics of Glauconite Sands

Glauconite is a dioctahedral potassium and iron rich 2:1 interlayer-deficient mica clay of the illite family. It has been referred to as “greensand”, comprising green peloidal sand-size grains which darken with maturity. Glauconite forms near the sediment-water interface in suboxic marine environments with low sedimentation rates. 

Glauconite formation, occurring across geologic epochs, peaked in the Cretaceous and persists in the Cenozoic, particularly in the 200-300 m water depth range on the North Atlantic continental margins. Odin and Matter (1981) proposed a four-stage evolution for glauconite, transitioning from nascent to highly evolved. The maturation process spans 10³ to 10⁶ years, with highly evolved glauconite having a residence time of 10⁵ to 10⁶ years.

Authigenic glauconite forms in situ, while reworked and redeposited glauconite is termed allogenic. Recent glauconite-bearing sediments are presumed to be primarily allogenic due to the prolonged formation of authigenic glauconite.

Geotechnical challenges associated with glauconite sands, primarily observed during the construction of ring roads around Antwerp, Belgium, involve peloidal glauconite content ranging from 35 to 65%. Issues with pipe and sheet pile driving refusal are linked to high pile wall shear resistance caused by particle crushing, fines content, and plasticity.

Recent North Sea monopile driving experiences confirm underpredicted resistance even for low glauconite content. Glauconite's crushability, compared to calcareous and carbonate soils, exhibits higher potential, impacting drilling progress, sampling, and driving resistance.

The characteristic response of glauconite sands is reflected in high cone tip resistance, sleeve friction, and friction ratios, yet existing classification charts are not calibrated for these soils. 

Five industry developers have financed the PIGS JIP to date, comprising

• Equinor
• Ørsted
• Avangrid
• Attentive Energy
• RWE

NGI is leading the project, with technical oversight and advisement provided by

• University of Massachusetts Amherst
• University of Massachusetts Dartmouth
• University of Arkansas
• Rutgers University
• Haley & Aldrich
• GRL Engineers

and an advisory panel of offshore geotechnical experts from:

• NTNU – Norwegian University of Science and Technology
• DNV
• Ghent University 

Below is a list of publications concerning glauconite sand behaviour and its implications for U.S. East Coast offshore wind development. Although additional publications will emerge from all PIGS activities after the expiration of established confidentiality periods, the list provided encompasses the broader research output related to glauconite produced by the research team.

The possible threats posed by glauconitic soil deposits to offshore wind farm construction have also attracted the interest of the general public, as is testified by this article published in The New Bedford Light on October 19, 2023: “A tricky, sticky mineral that’s challenging offshore wind developers on the East Coast - The New Bedford Light”.

• Westgate, Z. J., McMullin, C., Zeppilli, D., Beemer, R. D., & DeGroot, D. J. (2022). Geological and geotechnical characteristics of glauconitic sands. In Geo-Congress 2022 (pp. 113-121).
• Westgate, Z., McMullin, C., & DeGroot, D. (2022). Glauconite sand challenges for US offshore wind development. In International Conference on Offshore Mechanics and Arctic Engineering (Vol. 86618, p. V001T02A002). American Society of Mechanical Engineers.
• Westgate, Z. J., DeGroot, D. J., McMullin, C., Zou, Y., Guo, D., Van Haren, S., Beemer, R. D., Zeppilli, D., Miller, K. G., & Browning, J. V. (2023). Effect of degradation on geotechnical behavior of glauconite sands from the US Mid-Atlantic Coastal Plain. Ocean Engineering, 283, 115081.
• DeGroot, D. J., Westgate, Z. J., & Yetginer-Tjelta, T. I. (2023). Geological and geotechnical challenges for US offshore wind development. In 9th International SUT Offshore Site Investigation and Geotechnics (OSIG) Conference (pp. 82-111) – keynote paper.
• Geyin, M., Madyarova, M. M., Dantal, V., & Kassa, H. M. (2023). SBI-Based interbeddedness index for the prediction of glauconitic materials for offshore geotechnics. In 9th International SUT Offshore Site Investigation and Geotechnics (OSIG) Conference (pp. 112-117).
• King, T., Wuenscher, T., Griffiths, L., & Fraps, A. (2023). A novel approach to quantifying glauconite content in soils using digital image analysis. In 9th International SUT Offshore Site Investigation and Geotechnics (OSIG) Conference (pp. 118-123).
• Westgate, Z. J., Beemer, R. D., & DeGroot, D. J. (2023). Implications of glauconite sands on US offshore wind development. In 9th International SUT Offshore Site Investigation and Geotechnics (OSIG) Conference (pp. 124-131).
• Quinteros, V. S., Westgate Z. J., Vinck, K., Dantal, V., Lindtorp, A., & Toma, M. A. (2023). Interface friction angle of glauconitic sands for pile design. In 9th International SUT Offshore Site Investigation and Geotechnics (OSIG) Conference (pp. 155-161).
• Zeppilli, D., Dennis, E., Westgate, Z., Zhang, G., DeGroot, D., Miller, K. G., Browning, J., & Beemer, R. D. (2024). Atterberg limits of two crushed and natural glauconite soils. In Geo-Congress 2024 (pp. 177-186).
• Westgate, Z. J., Rahim, A., Senanayake, A., Pisano, F., Maldonado, C., Ridgway-Hill, A., Perikleous, Y., De Sordi, J., Roux, A., Andrews, E., & Ghasemi, P. (2024). The Piling in Glauconitic Sands (PIGS) JIP: reducing geotechnical uncertainty for U.S. offshore wind development. In Offshore Technology Conference (OTC) – accepted for publication