Norwegian Geotechnical Institute (NGI) Digital Archive
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Yield Stresses in Soft Contracting Clays
Get PDFThe undrained shear strength su along an arbitrary failure plane can be expressed as: su = 1/2(σ'ULS − σ'LLS) (1) where σ'ULS and σ'LLS denote the upper (U) and lower (L) effective, normal, compressive failure stresses acting at angles of +45 and −45° with the failure plane. These limiting stresses represent values that cannot be exceeded without yield occurring. In this paper, a study was done to investigate how the friction and attraction are mobilised by the plastic and elastic deformations to which the clay has been subjected. It is then possible to express undrained shear strength as a function of the consolidation stresses and two effective stress-strength parameters, the relative material attraction χ, and the effective material friction angle, sinϕ'M. The proposed theory forms the basis for constructing so-called yield envelopes for a clay, based on these strength parameters
Exploring seismic detection and resolution thresholds of fault zones and gas seeps in the shallow subsurface using seismic modelling
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Predicting permanent slope displacements due to multidirectional earthquake shaking from unidirectional shaking analyses
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Comparison of the condition of steel fiber-reinforced shotcrete with water-glass and alkali-free activators after more than 20 years of service in a subsea road tunnel
Get PDFThe in-service condition of steel fiber-reinforced shotcrete installed more than 20 years ago as single-shell rock support lining in the Nordkapp subsea road tunnel was investigated. The novelty of this study is the comparison of shotcrete with water–glass and alkali-free activators in a saline groundwater environment. The lowest shotcrete density was obtained at joints between two adjacent shotcrete layers. In the case of alkali-free accelerator, ettringite enrichment was observed in these joints. Leaching appeared to be the main degradation mechanism in the outermost 10–15 cm towards the traffic room
Extreme precipitation-induced landslide event on 30th July 2019 in Jølster, western Norway
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Weight of evidence tools in the prediction of acute fish toxicity
Get PDFAcute fish toxicity (AFT) is a key endpoint in nearly all regulatory implementations of environmental hazard assessments of chemicals globally. Although it is an early tier assay, the AFT assay is complex and uses many juvenile fish each year for the registration and assessment of chemicals. Thus, it is imperative to seek animal alternative approaches to replace or reduce animal use for environmental hazard assessments. A Bayesian Network (BN) model has been developed that brings together a suite of lines of evidence (LoEs) to produce a probabilistic estimate of AFT without the testing of additional juvenile fish. Lines of evidence include chemical descriptors, mode of action (MoA) assignment, knowledge of algal and daphnid acute toxicity, and animal alternative assays such as fish embryo tests and in vitro fish assays (e.g., gill cytotoxicity). The effort also includes retrieval, assessment, and curation of quality acute fish toxicity data because these act as the baseline of comparison with model outputs. An ideal outcome of this effort would be to have global applicability, acceptance and uptake, relevance to predominant fish species used in chemical assessments, be expandable to allow incorporation of future knowledge, and data to be publicly available. The BN model can be conceived as having incorporated principles of tiered assessment and whose outcomes will be directed by the available evidence in combination with prior information. We demonstrate that, as additional evidence is included in the prediction of a given chemical's ecotoxicity profile, both the accuracy and the precision of the predicted AFT can increase. Ultimately an improved environmental hazard assessment will be achieved.acceptedVersio
Microplastic in sediments and fauna. Offshore and inshore
Get PDFSamples of sediment and sediment-dwelling organisms were obtained from the Norwegian Continental Shelf and fjords in Southern Norway. These are referred to as offshore areas and inshore areas, respectively. The sediments samples in inshore areas had significantly higher concentrations of microplastics/kg dw. (mean ± SD: 6 132 ± 5 537) than the offshore sediments (mean ± SD: 1 298 ± 788). This is most likely due to closer proximity to anthropogenic influences and sources of plastic emissions, as well as the presence of accumulation areas of marine debris closer to the coastline. The inshore polychaeta samples trended towards higher concentrations of microplastic items/g w.w. (mean ± SD: 1 773 ± 2 598), than the offshore polychaeta (mean ± SD: 485 ± 607), though due to the large statistical variations in individual biota samples, this cannot be considered statistically significant The most frequently detected plastic polymers were polyolefins (PE, PP), chlorinated-polyethers (PVC, chlorinated PE), PS and rubber in both sediments and polychaeta samples, however there was also large variation in polymer composition between corresponding sediment and polychaeta samples. The environmental impact of microplastics on benthic ecosystems are unknown and in need pf further investigation. The anticipated concentrations of microplastics are expected to increase in the foreseeable future, potentially leading to threshold concentrations, so it is of relevance to repeat this monitoring exercise to account for this. In general the study in this survey were comparable with that of a previous survey also looking at microplastic and sediment concentrations in this region, though some of the polychaete concentrations were higher in this study, but nevertheless the biota-to-sediment enrichment factors (11 to 4 864 gd.w/ gw.w.) were on the low range of the previous study (100 to 11 000 11 to 4 864 gd.w/ gw.w.)
The effects of soil organic matter on leaching of hexavalent chromium from concrete waste: Batch and column experiments
Get PDFConcrete is one of the most common building materials in the world and in accordance with the world’s shift to a circular economy, there is a need of an increase in concrete reuse and recycling. One of the environmental concerns linked to concrete recycling is the leaching and spread of hexavalent chromium (Cr(VI)). In the present study the Cr(VI) leaching from crushed concrete waste and the effects of soil organic matter (SOM) on chromium (Cr) speciation has been investigated in realistic reuse scenarios by the means of batch shale tests and layered column tests. The effects of concrete properties (pH, grain size and age) on Cr(VI) leaching was also studied. Cr leaching from concrete alone is mainly in the form of Cr(VI), with the pH of the leachate being >10. The smaller the grainsize of the concrete, the higher the Cr(VI) concentration is in the leachate. There was no correlation between the age of the concrete and concrete leaching. When exposed to SOM the Total-Cr concentration in the leachate was reduced. The reduction increased with higher TOC level, with a 99% reduction at very high TOC (25%). The results indicate that Cr(VI) leaching from recycled concrete waste can be mitigated by exposing it to SOM in the desired recycling scenario.publishedVersio
Monitoring geological storage of CO2 using a new rock physics model
Get PDFTo mitigate the global warming crisis, one of the effective ways is to capture CO2 at an emitting source and inject it underground in saline aquifers, depleted oil and gas reservoirs, or in coal beds. This process is known as carbon capture and storage (CCS). With CCS, CO2 is considered a waste product that has to be disposed of properly, like sewage and other pollutants. While and after CO2 injection, monitoring of the CO2 storage site is necessary to observe CO2 plume movement and detect potential leakage. For CO2 monitoring, various physical property changes are employed to delineate the plume area and migration pathways with their pros and cons. We introduce a new rock physics model to facilitate the time-lapse estimation of CO2 saturation and possible pressure changes within a CO2 storage reservoir based on physical properties obtained from the prestack seismic inversion. We demonstrate that the CO2 plume delineation, saturation, and pressure changes estimations are possible using a combination of Acoustic Impedance (AI) and P- to S-wave velocity ratio (Vp/Vs) inverted from time-lapse or four-dimensional (4D) seismic. We assumed a scenario over a period of 40 years comprising an initial 25 year injection period. Our results show that monitoring the CO2 plume in terms of extent and saturation can be carried out using our rock physics-derived method. The suggested method, without going into the elastic moduli level, handles the elastic property cubes, which are commonly obtained from the prestack seismic inversion. Pressure changes quantification is also possible within un-cemented sands; however, the stress/cementation coefficient in our proposed model needs further study to relate that with effective stress in various types of sandstones. The three-dimensional (3D) seismic usually covers the area from the reservoir's base to the surface making it possible to detect the CO2 plume's lateral and vertical migration. However, the comparatively low resolution of seismic, the inversion uncertainties, lateral mineral, and shale property variations are some limitations, which warrant consideration. This method can also be applied for the exploration and monitoring of hydrocarbon production