Norwegian Geotechnical Institute

The Gulf of Bothnia presents notable challenges for offshore wind development due to its metocean and geological conditions. The seabed substrate varies widely, from soft post-glacial sediments to dense glacial tills and mixed outwash deposits, with bedrock locally close to or outcropping at the seabed. These hard soils provide suitable conditions for gravity-based foundations (GBFs), but reliable design requires an understanding of cyclic soil behaviour under loading from wind, waves, and winter ice. This study evaluates the cyclic shear strength of glacial soils using Direct Simple Shear (DSS) contour diagrams derived from established databases and representative load histories from the Baltic and North Seas, with the aim of supporting preliminary GBF design in glacial environments. The influence of key soil properties, such as plasticity, density, and consolidation state, and the effects of partial drainage are assessed. The study also discusses key uncertainties associated with database representativeness, cyclic contour and stress-path selection, and load history generalisation. The results enhance the reliability of early-stage GBF assessments and support the sustainable development of offshore wind infrastructure in the Gulf of Bothnia and similar glaciated seabed conditions. • Cyclic shear strengths obtained from an established DSS database. • Glacial soil behaviour evaluated under offshore storm loading. • Partial drainage shown to enhance cyclic resistance in sands. • Density and fines content strongly influence cyclic response. • Database-based cyclic strengths support early GBF design.

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.

The growing availability of IoT-enabled sensor networks has transformed how slope stability is monitored within Landslide Early Warning Systems (LEWS), producing vast datasets on pore pressures, groundwater levels, displacements, and external drivers such as rainfall. In the literature, there is an increased trend to apply advanced data analysis approaches and surrogate models to support slope stability assessment and early warning. However, the sheer volume and complexity of these data often limit users’ ability to interact with them in a flexible and intuitive way. Emerging advances in multi-modal generative AI models and agentic frameworks suggest a new paradigm: chat-with-your-data.In this approach, users interact directly with slope monitoring data through natural language, requesting tailored visualizations, summaries, analyses, or forecasts without the need for bespoke coding or rigid workflows. In the context of slope stability assessment and early warning, a practitioner could ask for recent pore pressure trends, rainfall-displacement correlations, threshold exceedances, or anticipated changes in stability conditions based on forecasted meteorological inputs for a specific site. The system identifies the relevant data sources, retrieves data, performs the required operations, and returns insights in user-friendly formats such as maps, diagrams, or downloadable datasets.The potential benefits include more direct access to relevant data and analyses, uncovering correlations, and enabling real-time decision support. However, challenges remain. These include ensuring that project-level access controls are respected, handling heterogeneous geospatial references, providing tailored data representations across spatial scales, and maintaining transparency and reliability in automatically generated outputs. Addressing these issues requires combining domain-specific knowledge in slope stability and landslide processes with expertise in generative AI and data governance.This work outlines a vision for how conversational interfaces could enhance slope-scale Landslide Early Warning Systems by supporting monitoring, modelling, and forecasting activities through intuitive human–data interaction. By allowing experts to query their data directly, we move toward systems that are more adaptable, interpretable, and insight-driven, promoting more effective use of monitoring data for targeted warning and risk mitigation.

The offshore wind industry faces critical challenges from rapid turbine size growth, limited installation vessel capacity, and the need to extend the service life of aging infrastructure. With wind turbine generators reaching 26 MW and monopiles expected to exceed 2500 t by 2030, up to half of European installation vessels may become unsuitable for these heavy foundations. This study evaluates hybrid monopile foundations as next-generation solutions integrating conventional monopiles with supporting structures such as footings, collars, or suction buckets. A review of hybrid foundation concepts is first presented, including monopile-footing, collared monopile, monopile-bucket, and monopile-three-bucket configurations, along with their installation methodologies and associated challenges. Finite element simulations using the NGI-ADP constitutive model in soft clay demonstrate that hybrid foundations can outperform conventional monopiles of equal steel volume. The monopile-bucket and monopile-three-bucket provide the highest lateral capacity, improving performance by up to 21.4 %. Staged installation allows the use of smaller vessels but introduces additional complexity in installation sequencing. Field deployments at Kaskasi (collared monopile) and Putian Pinghai Bay OWF (monopile-bucket) demonstrate practical feasibility. Hybrid foundations represent a strategic approach that accommodates installation constraints, optimizes material use, and enables foundation improvement to extend offshore wind turbine service life. • Hybrid monopiles are considered as next-generation solutions for addressing offshore wind foundation challenges. • Four hybrid concepts are evaluated: footing, collar, single-bucket, and three-bucket. • Staged installation of hybrid monopiles lowers vessel demand and field trials confirm practical feasibility. • Finite element results show bucket hybrids outperform monopiles with equal steel volume.

This study investigates the effect of overburden stress (effective confining stress) on liquefaction triggering using the largest cyclic test dataset ever applied to this crucial topic. The dataset includes 225 overburden stress correction factor (Kσ) values derived from a wide range of confining stresses, relative densities, and fine contents. Our analysis reveals that specimen preparation methods, particularly tamping and compaction, significantly affect Kσ values. Compaction stresses due to tamping and compaction induce an overconsolidation ratio that changes with confining pressure, which may produce a larger apparent effect of confining pressure on Kσ. We propose a new model for estimating Kσ for clean, normally consolidated sands, which shows less dependence on confining pressure and relative density than existing models. The effect of fines content on Kσ could not be isolated from other effects because fine-grained specimens in prior research were generally prepared using tamping and compaction methods. The proposed Kσ model is intended to isolate the effect of overburden stress, enabling its use in liquefaction triggering models where different effects are accounted for by distinct correction factors.

Silty sand in the offshore Yuedong area exhibits static mechanical behaviour strongly influenced by fines content (FC) and density. To characterize this behaviour and inform geotechnical design, a series of monotonic triaxial compression tests under drained and undrained conditions was conducted on reconstituted Yuedong silty sand with FC from 0–50%. The results show that increasing FC consistently reduces the shear strength and friction angle with no evidence of a threshold fines content (TFC) for strength minima within the tested FC range of 0–50%, which is believed due to the low particle size ratio of the Yuedong silty sand. A high FC suppresses dilatancy and increases liquefaction susceptibility under undrained conditions. The mechanical behaviour is governed by the interaction of FC and void ratio (e 0). All specimens ultimately converged to a unique critical state line, indicating a constant critical state friction angle (∼31°) independent of fines content. Crucially, the CSL in the e–log p′ plane shifts downward with increasing FC, resulting in a growing state parameter (ψ = e−e cs) and reduced dilatancy potential at the same void ratio. These findings demonstrate the applicability of the critical state soil mechanics (CSSM) framework to high-FC silty sands, and unify the influence of FC, e 0, and stress level into a coherent interpretative model. This study advances the fundamental understanding of silty sand behaviour and provides valuable guidance for strength parameter determination and geotechnical design in Yuedong silty sand and similar materials.

Sea-ice algae account for a substantial part of annual primary production in ice-covered waters and are an important component of the Arctic marine food web. With climate-induced changes to snow and sea-ice cover and their impact on the surface ocean, such as earlier melt, thinner ice, and increased upper-ocean stratification, a shift toward earlier and more extensive nutrient limitation on ice algal growth can be expected. Therefore, increasing our understanding of the processes governing nutrient supply and uptake by sea-ice algae is essential. Here, we compiled a pan-Arctic dataset of concentrations of sea-ice and sub-ice nutrients and sea-ice chlorophyll a (chl a) to assess their regional and seasonal variability, as well as the relationship of sea-ice algae and nutrient dynamics in the Arctic Ocean. This dataset indicates that bottom sea-ice nutrient and chl a concentrations were highest in the central Canadian Arctic Archipelago (Resolute Passage) due to tidal-driven mixing at the ocean-ice interface, and lowest in the Arctic Ocean basins. At the regional scale, Pacific and Atlantic Water influence variability in sea-ice and sub-ice nutrient concentrations. Significant positive relationships of bottom sea-ice nutrient versus chl a concentrations were ubiquitous across the Arctic during the ice algal bloom, suggesting intracellular nutrient storage as an important mechanism to support ice algal growth. This relationship in turn alters nutrient ratios within the sea ice relative to sub-ice waters, decreasing NOx:PO4 ratios, while increasing NOx:Si(OH)4 ratios. In contrast, bottom sea-ice nutrient-chl a relationships were less common and sometimes negative when nutrient concentrations were low, likely reflecting nutrient limitation. In conclusion, we have demonstrated a pan-Arctic, yet regionally specific, influence of the ice algal community on bottom sea-ice nutrient concentrations.