Time filter

Source Type

Oslo, Norway

Norwegian Geotechnical Institute NGI is a leading international centre for research and consulting within the geoscience. NGI develops optimum solutions for society, and offers expertise on the behaviour of soil, rock and snow and their interaction with the natural and built environment. NGI is a private foundation with office and laboratory in Oslo, branch office in Trondheim and daughter company in Houston, Texas, USA, and during 2014 a daughter company will be established in Perth, Australia. NGI was awarded Centre of Excellence status in 2002.The core competence is within geotechnics, engineering geology, hydrogeology and environmental geotechnology, with expertise within geomaterial properties and behaviour, numerical modelling and analysis, and instrumentation and monitoring. NGI's strength lies in the expertise of its personnel working in collaboration with clients and cooperating partners, to find practical solutions for the industry and society. NGI works within the following sectors: Offshore energy - Building, Construction and Transportation - Natural Hazards - Environmental Engineering. NGI has the honour to be the custodian of the Terzaghi and Peck Libraries. All academic material from Karl von Terzaghi and his colleague Ralph B. Peck has been given to NGI to be available for interested researchers.NGI was the host of the International Centre for Geohazards from 2003-2012, one of Norway's first Centres of Excellence . NGI's partners were NORSAR, the Norwegian Geological Survey , the University of Oslo and the Norwegian University of Science and Technology . Wikipedia.

Gauer P.,Norwegian Geotechnical Institute
Cold Regions Science and Technology | Year: 2014

Besides the runout distance of an avalanche information on avalanche intensity along the path is often required for hazard zoning or planning of mitigation measures. The avalanche (front) velocity is a common intensity measure as it can be linked to expected impact pressures. Furthermore, the velocity of an avalanche determines if the avalanche stays in its usual track or if the avalanche unexpectedly deviates and thus endangers areas believed to be safe. Therefore, a reliable prediction of the expected velocities is most important. However, many of the prevailing avalanche models either tend to underestimate velocities or they overestimate the runout distances.In this paper, several avalanche front velocity measurements from the Ryggfonn test site are presented. The measurements are derived from photo and/or video analyses of mainly dry-mixed avalanches. Some of these observations are partly supplemented by Doppler radar measurements.Additionally, the measurements from the Ryggfonn test site are compared with published velocity measurements from other locations to obtain a wider spectrum of avalanche conditions. By analyzing these velocities, constraints for possible rheological models of avalanche flows are obtained.The measurements of the presented avalanches, of which the most were relatively large to their path and can be classified as dry-mixed avalanches (i.e. they were partially fluidized and accompanied by a powder cloud), suggest a lower (apparent) velocity dependency of the bottom friction term than generally believed. The measurements show that the maximum front velocities of these avalanches scale with the square root of the total fall height of the avalanche front, that is, the maximum velocity Um∝Hsc. © 2013 Elsevier B.V.

Rathje E.M.,University of Texas at Austin | Saygili G.,Norwegian Geotechnical Institute
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2010

Permanent sliding displacements are used to evaluate the seismic stability of earth slopes, and current practice utilizes a pseudoprobabilistic approach to predict the expected sliding displacement. The pseudoprobabilistic approach specifies a design ground-motion level based on a probabilistic seismic hazard analysis and a specified hazard level (e.g., 2% probability of exceedance in 50 years), but the displacement is predicted deterministically based on the design ground-motion level. The fully probabilistic approach develops a hazard curve for sliding displacement, and it is used to assess the displacement of the slope for a given hazard level. Comparisons of the fully probabilistic and pseudoprobabilistic approaches indicate that the pseudoprobabilistic analysis provides nonconservative estimates of sliding displacement in most cases. This paper presents a modification to the pseudoprobabilistic approach that provides displacement values more consistent with the fully probabilistic approach. This modification involves specifying a displacement greater than the median, in order to take into account the uncertainty in the displacement prediction. The appropriate value of displacement above the median is a function of the ky/PGA value and the model used to predict the displacement. © 2011 American Society of Civil Engineers.

Berre T.,Norwegian Geotechnical Institute
Canadian Geotechnical Journal | Year: 2014

The tests in this investigation were performed on a natural soft clay with plasticity index around 32%, which was K0 consolidated to a vertical stress of 2942 kPa and then K0 unloaded to a vertical stress of 74 kPa (i.e., to the “in situ” stress). The specimens so created were disturbed in various ways to study the effect of sample disturbance on the stress–strain relationships during undrained shearing and during drained K0 loading (i.e., K0 triaxial and oedometer tests). The results for two testing alternatives may be summarized as follows. Alternative 1: Allow the specimen to swell at the correct in situ effective stresses, but accept an initial water content that is higher than the in situ value. This alternative was found to give the best stress–strain relationships around the in situ effective stresses for undrained triaxial tests, but with undrained shear strength values up to about 20% too low, due to the swelling taking place during consolidation to the in situ effective stresses. Alternative 2: Prevent swelling by starting the test at effective stresses that are higher than the in situ stresses, but with a water content that is closer to the in situ value than if alternative 1 is chosen. Using only isotropic stresses prior to shearing, this alternative was found to give better undrained shear strength values (although up to about 14% too high) but strain values much too small around the in situ effective stresses. For oedometer tests, only alternative 2 was investigated. Also, for these tests, the strains around the in situ stress were too small, but preconsolidation stresses estimated from stress–strain curves were typically only around 60% of the true value. © 2014 National Research Council of Canada. All rights reserved.

Du J.,Wuhan University | Yin K.,Wuhan University | Lacasse S.,Norwegian Geotechnical Institute
Landslides | Year: 2013

The prediction of active landslide displacement is a critical component of an early warning system and helps prevent property damage and loss of human lives. For the colluvial landslides in the Three Gorges Reservoir, the monitored displacement, precipitation, and reservoir level indicated that the characteristics of the deformations were closely related to the seasonal fluctuation of rainfall and reservoir level and that the displacement curve versus time showed a stepwise pattern. Besides the geological conditions, landslide displacement also depended on the variation in the influencing factors. Two typical colluvial landslides, the Baishuihe landslide and the Bazimen landslide, were selected for case studies. To analyze the different response components of the total displacement, the accumulated displacement was divided into a trend and a periodic component using a time series model. For the prediction of the periodic displacement, a back-propagation neural network model was adopted with selected factors including (1) the accumulated precipitation during the last 1-month period, (2) the accumulated precipitation over a 2-month period, (3) change of reservoir level during the last 1 month, (4) the average elevation of the reservoir level in the current month, and (5) the accumulated displacement increment during 1 year. The prediction of the displacement showed a periodic response in the displacement as a function of the variation of the influencing factors. The prediction model provided a good representation of the measured slide displacement behavior at the Baishuihe and the Bazimen sites, which can be adopted for displacement prediction and early warning of colluvial landslides in the Three Gorges Reservoir. © 2012 Springer-Verlag.

Havelsrud O.E.,Norwegian Geotechnical Institute
BMC microbiology | Year: 2011

Methane oxidizing prokaryotes in marine sediments are believed to function as a methane filter reducing the oceanic contribution to the global methane emission. In the anoxic parts of the sediments, oxidation of methane is accomplished by anaerobic methanotrophic archaea (ANME) living in syntrophy with sulphate reducing bacteria. This anaerobic oxidation of methane is assumed to be a coupling of reversed methanogenesis and dissimilatory sulphate reduction. Where oxygen is available aerobic methanotrophs take part in methane oxidation. In this study, we used metagenomics to characterize the taxonomic and metabolic potential for methane oxidation at the Tonya seep in the Coal Oil Point area, California. Two metagenomes from different sediment depth horizons (0-4 cm and 10-15 cm below sea floor) were sequenced by 454 technology. The metagenomes were analysed to characterize the distribution of aerobic and anaerobic methanotrophic taxa at the two sediment depths. To gain insight into the metabolic potential the metagenomes were searched for marker genes associated with methane oxidation. Blast searches followed by taxonomic binning in MEGAN revealed aerobic methanotrophs of the genus Methylococcus to be overrepresented in the 0-4 cm metagenome compared to the 10-15 cm metagenome. In the 10-15 cm metagenome, ANME of the ANME-1 clade, were identified as the most abundant methanotrophic taxon with 8.6% of the reads. Searches for particulate methane monooxygenase (pmoA) and methyl-coenzyme M reductase (mcrA), marker genes for aerobic and anaerobic oxidation of methane respectively, identified pmoA in the 0-4 cm metagenome as Methylococcaceae related. The mcrA reads from the 10-15 cm horizon were all classified as originating from the ANME-1 clade. Most of the taxa detected were present in both metagenomes and differences in community structure and corresponding metabolic potential between the two samples were mainly due to abundance differences. The results suggests that the Tonya Seep sediment is a robust methane filter, where taxa presently dominating this process could be replaced by less abundant methanotrophic taxa in case of changed environmental conditions.

Discover hidden collaborations