Norwegian Geotechnical Institute (NGI) Digital Archive
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Effect of kinematic interaction on seismic response of offshore wind turbines on monopiles
Get PDFInterest in renewable energy over the past decade has motivated a remarkable research on offshore wind energy. Due to the environmental loading conditions in the early developments of offshore wind farms, the focus of the research and engineering has been on aerodynamic and hydrodynamic subjects. However, earthquake has turned out to be a major design concern in seismic areas such as East Asia, Southern Europe, and United States. The topics include, among others, nonlinear response of foundations, soil liquefaction, and their impacts on foundation performance. An important topic in seismic soil‐structure interaction (SSI) analysis is the kinematic seismic response of foundations. This information is crucial for analyses based on the substructuring approach where both kinematic response and foundation impedances are key parameters. While considerable research has been spent on the latter topic, very little has been reported on the kinematic interaction. Large monopoles with low aspect ratios tend to rotate much more than regular piles in pile group foundations due to seismic waves. The rotation leads to additional load on the tower and the turbine. This article uses a rigorous numerical model for monopole‐soil interaction in layered soil and computes both rotational and horizontal responses at the pile head (seabed) as functions of frequency. A suite of generic homogeneous and heterogeneous soil profiles with shear moduli representative of clay (generally linear) and sand (generally parabolic) are considered in these analyses. Through representative analyses, both in frequency domain and time domain, it is illustrated how the kinematic interaction influences the earthquake loads imparted to an offshore wind turbine (OWT).acceptedVersio
Benchmark study of undrained triaxial testing of Opalinus Clay shale: Results and implications for robust testing
Get PDFTriaxial testing of argillaceous rocks and shales is significantly more challenging than conventional rock mechanical testing. The challenges are mainly related to the very low permeability of these geomaterials, and their sensitivity to exposure of atmosphere and brines, which induces variations of water content, suction and effective stress. There are currently no international standards to guide service laboratories for robust testing procedures for shales. A benchmark study of undrained triaxial testing was therefore initiated with three leading service laboratories in shale testing, performing 13 tests and using two different methods of establishing sample saturation prior to deformation. Both methods paid particular attention to minimize volume expansion of the specimens during saturation, and the loading rate during the shear phase in all tests was selected based on intrinsic sample properties and drainage configurations to ensure pore fluid pressure equilibration across the specimen. Opalinus Clay shale core material from the Mont Terri underground research laboratory was used for testing specimens, and intervals on cores were pre-selected on the basis of computer tomography to minimize material heterogeneity. A detailed diagnostic analysis of all tests was performed, and a comparison of the testing results is presented. Good reproducibility of the effective stress paths was achieved by the different laboratories for tests at identical or near-identical initial effective stress conditions. In particular, the test results over a larger range of effective stresses indicate very similar evolution of the fluid pressure during testing and a consistent picture for the derivation of global material properties. On the example of Opalinus Clay, the study demonstrates that robust triaxial testing results can be achieved for shales if some key challenges are adequately addressed.publishedVersio
Bioactive Metabolites of Marine Origin Have Unusual Effects on Model Membrane Systems
Get PDFMarine sponges and soft corals have yielded novel compounds with antineoplastic and antimicrobial activities. Their mechanisms of action are poorly understood, and in most cases, little relevant experimental evidence is available on this topic. In the present study, we investigated whether agelasine D (compound 1) and three agelasine analogs (compound 2–4) as well as malonganenone J (compound 5), affect the physical properties of a simple lipid model system, consisting of dioleoylphospahtidylcholine and dioleoylphosphatidylethanolamine. The data indicated that all the tested compounds increased stored curvature elastic stress, and therefore, tend to deform the bilayer which occurs without a reduction in the packing stress of the hexagonal phase. Furthermore, lower concentrations (1%) appear to have a more pronounced effect than higher ones (5–10%). For compounds 4 and 5, this effect is also reflected in phospholipid headgroup mobility assessed using 31P chemical shift anisotropy (CSA) values of the lamellar phases. Among the compounds tested, compound 4 stands out with respect to its effects on the membrane model systems, which matches its efficacy against a broad spectrum of pathogens. Future work that aims to increase the pharmacological usefulness of these compounds could benefit from taking into account the compound effects on the fluid lamellar phase at low concentrationspublishedVersio
Building Deformation Caused by Tunneling: Centrifuge Modeling
Get PDFThis paper investigates the deformation of buildings due to tunneling-induced soil displacements. Centrifuge model tests of three-dimensionally (3D) printed building models subject to a plane-strain tunnel excavation in dense, dry sand are discussed. The small-scale structures replicate important building characteristics including brittle material properties similar to masonry, a realistic building layout, façade openings, strip footings, and a rough soil-structure interface. Digital images were captured during the experiments, enabling image-based measurements of the building response. Results demonstrate the essential role of the building-to-tunnel position and structural details (i.e., opening percentage and building length). The onset of building cracking and cracking patterns confirms the importance of the building-to-tunnel position and structural details. The tests illustrate that an increase in the façade opening area leads to increased shear deformations while longer buildings caused an increase in bending deflections. An evaluation of the widely accepted framework of treating a structure separately at either side of the greenfield inflection point shows that this procedure can underestimate building damage.acceptedVersio
Organic-rich shale caprock properties of potential CO2 storage sites in the northern North Sea, offshore Norway
Get PDFAssessment of the geomechanical properties of organic-rich shale caprocks is critical for a successful CO2 storage into a saline aquifer. In this study, we investigated the geochemical properties of the organic-rich shale caprocks of the Draupne and Heather formations, overlying the potential sandstone reservoirs of Sognefjord, Fensfjord, and Krossfjord formations in the northern North Sea, offshore Norway. The caprock’s depositional variations within the sub-basins are established by analyzing the gamma-ray shape and stacking patterns. The effect due to differences in depositional environments, on the caprock compaction behavior is investigated by integrating petrographical analysis of core and cutting samples from 3 wells and by rock physical analysis of wireline log data from 27 exploration wells. Three rock physics templates are used where the wireline log data are interpreted using the published background trends. The effect of kerogen type, maturation level, and deposition environment on caprock properties within the study area are also evaluated. Moreover, the caprock property, such as brittleness, is estimated by using four mineralogy and elastic property-based, empirical relations, which is a quantitative measure of caprock property with respect to changes in stress-state. Finally, the seismic inversion method is assessed for the possibility of extracting caprock properties from surface seismic data. Regardless of compaction processes, the results indicate that the Heather Formation is mechanically stronger than the Draupne Formation. However, both formations appear to be ductile in nature. The depositional environments control the mineralogical composition and fabric of the Draupne and Heather formations, which influence the caprock properties significantly. Results also show that the effect of TOC on caprock properties is insignificant in the study area. The brittleness of the organic-rich shale caprocks in the study area follows a different trend compared to the published trends. We also observed an excellent correlation between the log-derived elastic properties and geomechanical parameters. Still, it is difficult to assess the caprock elastic properties from seismic due to the overlap of data clusters. The evaluation of caprock geomechanical behaviors is challenging as these properties are site-specific and also influenced by other factors such as exhumation, in-situ stress conditions, the existence of natural fractures, and their orientations.publishedVersio
Structural analysis of the Smeaheia fault block, a potential CO2 storage site, northern Horda Platform, North Sea
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Effect of prior small to moderate seismic events on monotonic undrained shear strength of sand
Get PDFIn this study we investigate the effect of prior seismic shaking on the monotonic shear strength of saturated Ottawa Sand 20/30. We perform a series of stress-controlled undrained cyclic triaxial tests with different seismic intensities intentionally without causing failure, followed by drainage of the excess pore pressure and an un-drained monotonic loading test to determine the undrained shear strength. The experimental data show that small to moderate seismic events that do not fail the specimen can significantly increase undrained shear strength without much change in relative density. One prior seismic event with peak ground acceleration ~ 1.3 m/s2 may increase the undrained shear strength of a specimen at ~ 10 m depth by around 30%. The results also show that as the intensity of the shaking increases, the increase in the monotonic shear strength increases. However, the strengthening effect does not increase with the number of seismic events although a small degree of global densification in the sample is observed. The results of this paper will help assess the change in static slope stability after a single or multiple small to moderate events occurred without causing initial instability.publishedVersio
Deliverable 3.2. Capacity building material for the field trials
Get PDFIn Deliverable 3.1 (Deltares, 2019) the theoretical background, research questions, hypotheses (also summarized in Section 2 of this document) and overall method have been described. This deliverable focuses on the workflow in the field trials and provides capacity materials (templates) to carry out the research. The workflow and templates are meant to help to:
1. Select the climate service(s) that will be adapted for the EVOKED project;
2. Identify ‘usability-gap(s)’ between the information given by the climate service(s) and the information needs of the end-user(s);
3. Think about a new, improved information design (i.e. the way in which information is presented – for a more elaborate explanation on the concept we refer to Deliverbale 3.1 (Deltares, 2019) of the selected climate service(s) to help bridge the aforementioned ‘usability-gap’ through the way information is presented to the user of the climate service(s);
4. To test the new information design (as an experiment).
Finally, this document aims to create a coherent data management structure by using the same templates for each case study location. This enables both the cross-comparison between the case studies and the overall analysis regarding EVOKED-hypotheses.EU, Horizon Europe
European Research Area for Climate Services
JPI Climate
The Research Council of Norway
Federal Ministry of Education and Research (Germany)
NWO
FORMA
Effect of conservation farming and biochar addition on soil organic carbon quality, nitrogen mineralization, and crop productivity in a light textured Acrisol in the sub-humid tropics
Get PDFConservation farming (CF), involving basin tillage, residue retention and crop rotation, combined with biochar may help to mitigate negative impacts of conventional agriculture. In this study, the effects of CF on the amount and quality of soil organic matter (SOM) and potential nitrogen (N) mineralization were investigated in a maize-soya-maize rotation in an Acrisol in Zambia. A large field was run under CF for 7 years and in the subsequent three growing seasons (2015–2018), four management practices were introduced to study effects on soil characteristics and crop yield. We tested i) a continuation of regular CF (CF-NORM) ii) CF without residue retention (CF-NO-RES); iii) Conventional (CONV), with full tillage and removal of residues; and iv) CF with 4 ton ha-1 pigeon pea biochar inside basins and residue retention (CF-BC). The experiment involved the addition of fertilizer only to maize, while soya received none. Soya yield was significantly higher in CF systems than in CONV. Maize yields were not affected by the different management practices probably due to the ample fertilizer addition. CF-NORM had a higher stock of soil organic carbon (SOC), higher N mineralization rates, more hot-water extractable carbon (HWEC; labile SOC) and particulate organic matter (POM) inside basins compared to the surrounding soil (outside basins). Our results suggest that the input of roots inside basins are more effective increasing SOM and N mineralization, than the crop residues that are placed outside basins. CONV reduced both quality and quantity of SOM and N mineralization as compared to CF inside basins. CF-BC increased the amount of SOC as compared with CF-NORM, whereas N mineralization rate and HWEC remained unaffected. The results suggest benefits on yield of CF and none of biochar; larger impact of root biomass on the build-up of SOM than crop residues; and high stability of biochar in soil.publishedVersio