Fugro (United States)

The interface friction angle is a crucial design parameter for various foundations, including piles, suction buckets, anchors, gravity-based structures, pipelines, cables, and more. In the past decade, the exponential growth of offshore wind projects has led to a higher demand for multistage ring shear tests to mimic installation effects. Moreover, there is a need to obtain reliable interface friction angles, due to the potential savings in manufacturing, transportation, and installation of foundations, such as monopiles. To investigate the reliability of the interface friction angle obtained by laboratories worldwide, a round-robin testing program on interface shear tests of sand against rough steel is presented. This study focuses primarily on the most common ring shear devices, including the Bishop type and the Bromhead. Results from 42 ring shear tests conducted on 30 different devices across 19 laboratories (using the same sand and similar procedures) are presented and compared. The data suggest that the residual interface friction angle (δres) obtained from Bromhead can be 10% to 35% higher than that obtained from the Bishop ring shear apparatus. Significant scatter was observed in the results, as the Bishop ring shear yielded a δres=26.2°±0.8° (mean and standard deviation), while for the Bromhead devices, a δres=30.5°±3.5° (min=23.7° and max=39.4°) was derived, indicating that the Bromhead device could overestimate δres, in sand, by an average of approximately Δδres=4° or more. Additional tests revealed that careful specimen reconstitution is necessary to avoid creating extra friction between the sand and the confining rings in the Bromhead ring shear device. Furthermore, as suggested in previous studies, decreasing the settlements during consolidation (to <0.75 mm) does aid but does not eliminate side friction of the Bromhead device when testing a typical North Sea offshore sand in multistage shear testing. Finally, best practice recommendations are provided in this paper for obtaining more reliable interface friction angles on sand using Bromhead-type ring shear devices.

This study investigates the use of high-resolution 3D geometric data collected by unmanned aerial vehicles (UAVs) for estimating material properties in dam stability assessments following failure events. The analysis focuses on the Sparmos Dam in Greece, which collapsed in 2016 due to under seepage and at a different location due to rapid drawdown. UAVs provided timely, high-quality 3D data that allowed for the estimation of failure geometry. Using this data, 2D and 3D rapid drawdown analyses were conducted, applying the Duncan three-stage method to assess stability under rapid drawdown conditions. The comparison between the critical sliding blocks from the simulations and the failure surface captured by UAVs indicated that material properties such as undrained shear strength and overconsolidation ratio could be constrained effectively. This study demonstrates that UAV-collected data can provide valuable insights into failure mechanisms and serve as a rapid, reliable tool for post-disaster response, offering an understanding of dam stability before even sampling and laboratory testing results can be available.

ABSTRACT Thick rings represent a relatively recent solution implemented in laboratory testing practice to prevent slippage during shear at the interface between the soil specimen and the top and bottom caps of the direct simple shear system. The setup of a specimen with thick rings involves two additional rings, approximately 9 mm in thickness, placed at the top and bottom ends of the regular ring stack. In order to laterally confine the soil–cap interface, the end of the specimen lies inside the thick ring where it makes contact with the porous stone of the top or bottom cap. The addition of thick rings essentially moves the shear test boundary away from the plane of contact between the soil specimen and the porous stone into the soil at the end of the thick ring. This paper describes the setup of soil specimens with thick rings in relation to the conventional setup with no thick rings and evaluates the impact of thick rings on stress–strain-strength measurements obtained from constant volume monotonic and cyclic direct simple shear tests performed on a high-plasticity marine clay. Because of the test boundary offset in direct simple shear tests on specimens with thick rings, there is a need to introduce an effective shear height in the calculation of shear strains based on ASTM D6528-17, Standard Test Method for Consolidated Undrained Direct Simple Shear Testing of Fine Grain Soils. This is different from the total specimen height at the start of the shear phase currently used in shear strain calculations.

Abstract The Bureau of Ocean Energy Management (BOEM) has designated call areas within the Gulf of Maine outer continental shelf in water depths suitable for floating turbines (i.e., greater than 100 m). The objective of this study is to present an overview of the geologic and geophysical conditions and constraints within the Gulf of Maine where potential lease areas may be located. This work expands on the previous 2022 BOEM-funded desktop study supporting the US Department of the Interior, Bureau of Safety and Environmental Enforcement’s solicitation for areas of interest to the Bureau of Ocean Energy Management Technology Assessment Program on offshore wind technology (BAA No: 140M0121R0006) (Fugro 2022). The study utilized public domain geophysical and geotechnical data to evaluate the seafloor and near-seafloor geological and geotechnical conditions relevant to floating offshore wind. Data available from published scientific literature and offshore projects were integrated and evaluated using GIS and seismic interpretation software to identify and map geohazards, seabed and subsurface conditions, and key stratigraphic geotechnical units. These results are presented as maps illustrating seabed and subsurface conditions, including geohazards. Our evaluation of the study area indicates generally favorable conditions for offshore wind development, with site-specific considerations to be factored into engineering design. Key findings related to geological conditions include exposed bedrock, glacial deposits (including exposed glacial till and boulders), and very soft fine-grained sediments. Based on these conditions, the suitability of various foundation concepts is discussed. Other conditions include ocean usage, from fishing activities to vessel traffic. This paper will highlight potential geohazards and provide developers with an understanding of geological and geotechnical conditions in the call area. Understanding of geologic and geotechnical conditions will aid in feasibility assessment for floating wind developments within the Gulf of Maine call area.

Considering the benefits of understanding the circulation patterns of the shelf, it is not surprising that there are numerous studies of the Texas Shelf circulation patterns. Given that previous studies were focused on the low-frequency variability of the circulation which is upcoast (northeast flow) in the summer and downcoast (southwest flow) especially on the inner shelf in the non-summer seasons, this study investigates the weather band (2–15 days) variability of the Texas Shelf near-surface circulation pattern. Current meter data at 1.5 m below the sea surface from the inner, mid, and outer shelves were analyzed. This study demonstrated that there are high-frequency current reversals within the weather band in each season. From the estimated persistence of the currents during reversals, the inner and mid shelf currents are predominantly downcoast in the non-summer seasons and upcoast in the summer season whereas the outer shelf currents are mostly upcoast all year round. The Wavelets analysis of the currents revealed that most of the variabilities on the inner and mid shelf regions were within the 4-12-day band whereas on the outer shelf the dominant variability was within the 3–8-day band. From the cross-spectra analysis of both the currents and wind data, it was determined that the influence of the wind was more dominant on the inner and mid shelf regions at the 8–15-day band than on the outer shelf where the contribution of the wind is prevalent at the 2–4-day band.

In 2021-2022, two related validation studies were conducted on structural health monitoring of the Samuel de Champlain Bridge in the La Prairie Basin of the Saint Lawrence River near Montreal, Canada. In the first study, C-band satellite Interferometric Synthetic Aperture Radar (InSAR) observations of bridge line-ofsight thermal displacement measurements were compared to predicted values. A companion observational study of multispectral (MS) imagery assessed turbulent and flow features on the river’s surface that are indicative of changes in the riverbed morphology and used stereo MS imagery to derive river velocity vectors using a Particle Image Velocimetry (PIV) algorithm. This paper presents the preliminary findings of a follow-up study, in which timeseries of InSAR displacement observations at nine piers of the Samuel de Champlain Bridge were compared to water depth, ambient water surface temperature from satellite imagery, and ambient air temperature from a nearby in-situ weather station.

Abstract Offshore wind developers obtain extensive geophysical, geotechnical, and habitat data during Site Characterization activities. Integration and delivery of this information to a diverse group of stakeholders and Government agencies is required. We present an integrated benthic habitat mapping approach tailored to regional geology and ground conditions and discuss how various data was utilized to deliver multiple components of the permitting process. Multiple data sets were integrated and presented via a web-based GIS platform to aid delivery, visualization, and communication. Our unified approach to benthic habitat mapping and delivery of products to stakeholders was instrumental in successfully coalescing multiple performers to develop their individual deliverables in a cohesive and rapid manner. This approach reduced risk to schedule and budget, without sacrificing data density or quality. Four annual (2019–2022) benthic surveys were acquired to support Site Characterization and subsequent permitting processes. High-Resolution Geophysical data were collected concomitantly with the 2020 benthic survey data and used to refine subsequent 2021 and 2022 benthic survey designs. Benthic survey data consisted of grab sample tests (grain size), macrofaunal taxonomy, sediment profile and plan view imagery (SPI-PV), video imagery from each grab station, and towed video transects. Acoustic data products were processed and interpreted to create polygons of seafloor sediment coverage over the ASOW study area and ground-truthed with physical sampling, video, and digital still imagery to refine and validate acoustic data into a mappable model of essential fish and benthic habitats. Seafloor morphology and seabed sediment interpretations were coalesced into a benthic habitat model that displayed substrates consisting mostly of mobile sand sheets, with interspersed areas of gravelly sand and discrete patches of gravel. Overlying the substrate model was a range of benthic features and morphologies, including sand ridges, sand waves, megaripples, ripples, areas of depressional marks, hummocky seafloor, interbedded surficial sediments, irregular seafloor, and localized relief features. From these data, classified maps of Coastal Marine Ecological Standard (CMECS) substrates and fish habitats were made. Additional CMECS classification of benthic biotic components were mapped, showing the taxonomic communities that are present in each substrate. Seabed sediment modeling and morphological trends were dynamically studied and compiled into an interpreted and GIS-friendly dataset that enabled rapid online transfer to subject matter experts tasked with quantifying the benthic ecosystem across the development area. The methods and modeling that were produced by expert refinement of geophysical data to reflect the physically observed habitat structures allowed for dynamic minimum mapping unit variability while also isolating and identifying key areas of interest for benthic researchers and regulators. This mapping process led to an efficient and unified approach for all teams, saving project time and expense.

Abstract This study presents site-specific CPT-based correlation relationships for preconsolidation pressure, undrained shear strength, relative density and effective friction angle, developed for geotechnical characterization of foundation zone sediments at the Atlantic Shores offshore wind farm development. Results of laboratory geotechnical tests on samples from 49 soil borings performed at the Lease Area were correlated with corresponding measured cone resistance values from companion seabed or downhole CPTs. Ranges of overconsolidation ratios estimated using CPT-derived preconsolidation pressures from site-specific correlation relationships are in good agreement with overconsolidation ratios derived from laboratory measured preconsolidation pressures for various cohesive soil units. Interpreted ranges of cone resistance factors (i.e., Nkt) required in CPT-based undrained shear strength evaluation for cohesive soil units are significantly wider compared to the typical range of 15 to 20 representative for Gulf of Mexico clay sediments, as a result of large variability in soil plasticity as well as intermixed nature of the soils. Representative ranges of relative density and effective friction angle obtained from CPT data using site-specific correlation relationships, developed for the cohesionless soils at the Lease Area, are consistent with ranges of laboratory measured values.