Norwegian Geotechnical Institute (NGI) Digital Archive
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Effect of Shallow Slip Amplification Uncertainty on Probabilistic Tsunami Hazard Analysis in Subduction Zones: Use of Long-Term Balanced Stochastic Slip Models
Get PDFThe complexity of coseismic slip distributions influences the tsunami hazard posed by local and, to a certain extent, distant tsunami sources. Large slip concentrated in shallow patches was observed in recent tsunamigenic earthquakes, possibly due to dynamic amplification near the free surface, variable frictional conditions or other factors. We propose a method for incorporating enhanced shallow slip for subduction earthquakes while preventing systematic slip excess at shallow depths over one or more seismic cycles. The method uses the classic k−2 stochastic slip distributions, augmented by shallow slip amplification. It is necessary for deep events with lower slip to occur more often than shallow ones with amplified slip to balance the long-term cumulative slip. We evaluate the impact of this approach on tsunami hazard in the central and eastern Mediterranean Sea adopting a realistic 3D geometry for three subduction zones, by using it to model ~ 150,000 earthquakes with Mw from 6.0 to 9.0. We combine earthquake rates, depth-dependent slip distributions, tsunami modeling, and epistemic uncertainty through an ensemble modeling technique. We found that the mean hazard curves obtained with our method show enhanced probabilities for larger inundation heights as compared to the curves derived from depth-independent slip distributions. Our approach is completely general and can be applied to any subduction zone in the world.publishedVersio
Acoustic characterization of an artificial CO2 seep using split-beam echo sounders
Get PDFGeological carbon storage (GCS) has emerged as a promising method for reducing greenhouse gas emissions and achieving international climate goals. Currently, sub-seafloor GCS sites sequester about 1.8 MtCO2/yr. Additional sites are under development and by 2050, there is potential for storage of ≈ 100 Mt CO2/yr. For the expansion of sub-seafloor GCS to be successful, cost-efficient and effective leak monitoring systems must be available. The ACT4storage project is tasked with development of leak monitoring through the selection and use of available technologies. A part of the monitoring suite is the use of active acoustics to detect and quantify free CO2 bubbles and droplets. An artificial seep device was created to simulate leaks of CO2 bubbles. Leak simulations were quantified by two broadband split-beam echosounders (50-90 kHz and 250-450 kHz). The split-beam echosounders offer high sensitivity, broadband transmission and were calibrated to quantify flux from a leakage site. The split-beam echosounders show promise as cost-efficient and effective methods for the detection and quantification of free CO2.publishedVersio
Can polyethylene passive samplers predict polychlorinated biphenyls (PCBs) uptake by earthworms and turnips in a biochar amended soil?
Get PDFA pot experiment was carried out in which aged polychlorinated biphenyls (PCBs) contaminated soil was amended with biochar, and three phases; earthworms, turnips and polyethylene (PE) passive samplers, were added simultaneously in order to investigate changes in bioavailability of PCB following biochar amendment. Two biochars were used; one made from rice husk in Indonesia using local techniques and the other made from mixed wood shavings using more advanced technology. The biochars were amended at 1 and 4% doses. The overall accumulation of PCBs to the phases followed the order: earthworm lipid > PE > turnip. The rice husk biochar reduced PCB accumulation to a greater degree than the mixed wood biochar for all phases, however there was no effect of dose for either biochar. Earthworm uptake was reduced between 52% and 91% for rice husk biochar and by 19% to 63% for mix wood biochar. Turnip uptake was not significantly reduced by biochar amendment. Phase to soil accumulation factors (PSAF) were around 0.5 for turnips, approximately 5 for PE and exceeded 100 for earthworms. This study demonstrates that both biochars can be a sustainable alternative for in situ soil remediation and that PE can be used as tool to simulate the uptake in earthworms and thus remediation effectiveness.publishedVersio
Biochar amendment improves degraded pasturelands in Brazil: environmental and cost-benefit analysis
Get PDFMost deforested lands in Brazil are occupied by low-productivity cattle ranching. Brazil is the second biggest meat producer worldwide and is projected to increase its agricultural output more than any other country. Biochar has been shown to improve soil properties and agricultural productivity when added to degraded soils, but these effects are context-dependent. The impact of biochar, fertilizer and inoculant on the productivity of forage grasses in Brazil (Brachiaria spp. and Panicum spp.) was investigated from environmental and socio-economic perspectives. We showed a 27% average increase in Brachiaria production over two years but no significant effects of amendment on Panicum yield. Biochar addition also increased the contents of macronutrients, soil pH and CEC. Each hectare amended with biochar saved 91 tonnes of CO2eq through land sparing effect, 13 tonnes of CO2eq sequestered in the soil, equating to U$455 in carbon payments. The costs of biochar production for smallholder farmers, mostly because of labour cost, outweighed the potential benefits of its use. Biochar is 617% more expensive than common fertilizers. Biochar could improve productivity of degraded pasturelands in Brazil if investments in efficient biochar production techniques are used and biochar is subsidized by low emission incentive schemes.Biochar amendment improves degraded pasturelands in Brazil: environmental and cost-benefit analysispublishedVersio
Reservoir assessment of Middle Jurassic sandstone-dominated formations in the Egersund Basin and Ling Depression, eastern Central North Sea
Get PDFReservoir quality assessment was conducted from petrophysical analysis and rock physics diagnostics on 15 wells penetrating Middle Jurassic sandstone reservoir formations in different regions of the eastern Central North Sea. Seismic interpretation on available 3D and 2D seismic reflection data was utilized to map thickness variations and to draw broad correlations to structural features such as salt structures and faults. In the central Egersund Basin, the Sandnes Formation shows good reservoir properties (gross thickness = 107–147 m, N/G = 33–53%) while the Bryne Formation exhibits poorer reservoir quality (N/G < 20%). Both formations display variable reservoir properties and thicknesses on the northern flank of the Egersund Basin and in the Ling Depression (Sandnes Formation: gross thickness 16–26 m, N/G = 11–81%; Bryne Formation: 30–221 m, N/G = 25–70%). The time-equivalent Hugin and Sleipner formations are more locally developed in the southwest part of Ling Depression, and display good-to-excellent and intermediate reservoir quality, respectively. Furthermore, we use the outcomes of the conducted analyses to correlate observations to further exploration on various reservoir target formations and on seismic prediction of reservoir properties. Thus, the risk on reservoir presence and efficiency for the chased targets is considerably reduced. The main remaining risks within the study area are related to source rocks, their maturity, expulsion and migration of hydrocarbon, and the timing of trap formation.Reservoir assessment of Middle Jurassic sandstone-dominated formations in the Egersund Basin and Ling Depression, eastern Central North SeapublishedVersio
Numerical modeling of liquefaction and its impact on anchor piles for floating offshore structures
Get PDFAnchor piles and suction anchors have been used for anchoring different types of offshore structure in the past four decades. The recent growing interest and demand for wind energy has motivated the industry to evaluate the use of Offshore Wind Turbines (OWT) in deep waters for which floating wind turbine is a good alternative to bottom-fixed solutions particularly in seismic regions with possibility of soil liquefaction. Extensive research has been carried out to assess the consequences of soil liquefaction for buildings and onshore structures; however, this phenomenon has not been sufficiently studied for offshore foundations. This paper aims at investigating the use of advanced liquefaction modeling in assessment of the performance of anchor piles for offshore facilities and in particular floating offshore wind turbines. The software FLAC3D is used to carry out the nonlinear dynamic analyses using SANISAND constitutive model for saturated sand. The analyses indicate that SANISAND model is capable of correctly simulating the excess pore water pressure in the free-field as observed in centrifuge tests. Pore pressure build-up due to earthquake shaking together with earthquake-induced displacements are computed at various points in the soil medium containing an anchor pile in different scenarios. The numerical results indicate that anchor piles may experience permanent lateral displacements and tilt due to the combined action of static mooring load and earthquake shaking leading to soil liquefaction.Numerical modeling of liquefaction and its impact on anchor piles for floating offshore structure
Standardization of in situ tests and field work
Get PDFThe Norwegian Geo-Test Sites (NGTS) research infrastructure, with funding from The Research Council of Norway, creates a national research test site facility for geotech-nical research. The five national test sites are located in Norway and on Svalbard. The research consortium consists of NGI and NTNU, SINTEF/UNIS and NPRA (Norwegian Public Roads Administration). The research project aims at developing five sites as field laboratories for the testing and verification of innovative soil investigation and testing methods. The sites cover the soil conditions of soft clay, quick clay, silt, sand and per-mafrost. At the end of the project, the test sites will serve as reference sites for the in-dustry, public authorities, research organizations and academia where benchmarked data can be used by several generations of scientists and engineers to develop soil material models, new investigation methods, new foundation solutions and advance the state-of-the-art. The five sites will be operative for at least 10-20 yrs.
To ensure quality of the data generated in the project and to ensure as much uniformity of the results as possible it is important that all partners performing work at the sites follow the same test procedures and standards.
The present report give an overview of the main in situ testing methods and sampling techniques to be used in the NGTS project. Work at the NGTS sites shall be performed according to the referenced standards and requirements listed in the present report.Research Council of Norway (RCN
Leaching and transport of PFAS from aqueous film-forming foam (AFFF) in the unsaturated soil at a firefighting training facility under cold climatic conditions
Get PDFThe contaminant situation at a Norwegian firefighting training facility (FTF) was investigated 15 years after the use of perfluorooctanesulfonic acid (PFOS) based aqueous film forming foams (AFFF) products had ceased. Detailed mapping of the soil and groundwater at the FTF field site in 2016, revealed high concentrations of per- and polyfluoroalkyl substances (PFAS). PFOS accounted for 96% of the total PFAS concentration in the soil with concentrations ranging from <0.3 μg/kg to 6500 μg/kg. The average concentration of PFOS in the groundwater down-gradient of the site was 22 μg/l (6.5–44.4 μg/l), accounting for 71% of the total PFAS concentration...publishedVersio
Offshore Wind Turbine Foundations State of the Art
Get PDFThe huge growth and intense development in the European offshore wind power sector over the last decade have created significant achievements within the wind turbine foundation technology. The state of the art focusing on geotechnical design aspects for Offshore Wind Turbine (OWT) foundations and important aspects for installation are presented in this paper. In place operational experience based on structural health monitoring campaigns and future trends are also discussedpublishedVersio
Snow Avalanche Accident in the Tamok Valley, 2019-01-02
No full textFire utenlandske skituristerutløste et snøskred på topptur i Tamokdalen. Alle de fire omkom. Notatet beskriver skredfaglige faktorer.NVE (Norges vassdrags- og energidirektorat