Norwegian Geotechnical Institute (NGI) Digital Archive
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Design considerations of suction caisson foundations for offshore wind turbines in Southern China
Get PDFSuction caisson foundations are increasingly considered as a foundation solution for offshore wind farm development in China. This paper outlines the design considerations for developing a suction caisson supported jacket solution for an offshore wind farm in Southern China. Geotechnical analyses for four major aspects, ultimate limit state (ULS), serviceability limit state (SLS), fatigue limit state (FLS) and installation are discussed. The design challenges encountered in the project due to soft seabed and metocean characteristics (severe typhoon loading and dominant wind directions) and technical approaches adopted by the project are presented. Areas for further studies are identified and discussed. The purpose of this paper is to disseminate this knowledge and raise awareness of several important aspects.publishedVersio
Effect of reconstitution techniques on the triaxial stress-strength behaviour of a very dense sand
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Leveranse 5.2. Delprosjekt 5 – Risiko
No full textHensikten med verktøyet er å systematisk identifisere og vurdere risiko for uønskede hendelser. Risikomatrisen som genereres kan danne grunnlag for valg av anleggsmetoder og behov for avbøtende tiltak. Risikovurderingen vil også være mulig å oppdatere i ulike prosjektfaser og vil være nyttig ved kommunikasjon av risiko blant prosjektets ulike aktører
CPTU CORRELATIONS FOR CLAYS
Get PDFAs part of the R&D project GEODIP-SP8, a multivariate high-quality database of sensitive clays consisting of laboratory strength and consolidation test results, index parameters and CPTU parameters was established. The present report evaluates, with the help of multiple regression analyses, possible correlations among measured CPTU parameters (e.g. excess pore pressure, Δu, net cone resistance, qnet, and effective cone resistance, qe), undrained shear strength from CAUC tests (suC) and some basic clay properties (e.g., OCR, plasticity) included in the database.
The first part of the report presents the collected data points and it discusses sample quality. Then, correlations based on simple and multivariable linear regression analyses are proposed for undrained shear strength, overconsolidation ratio and preconsolidation stress. The goodness of the established correlations established is checked for seven test sites in Norway. Finally, recommendations for engineering practice are given based on the outcomes of this study
Investigation and geotechnical characterization of Perniö clay, Finland
Get PDFUnderstanding the behavior of soft sensitive clays is a key aspect of geotechnical design, especially in those regions where constructions are planned in marine clay areas. In Finland, one of the major geotechnical issues is the stability and deformation of the railway embankments located on soft soil deposits. The Tampere University of Technology (TUT) and the Finnish Transport Agency (FTA) have been carrying out a research project aiming to a better understanding of strength and deformation properties of Finnish soft clays. As a part of this project, a detailed site investigation was conducted at Perniö site in Western Finland. This paper presents the details of the geotechnical investigation, including field testing, sampling operations, and the laboratory testing program. In particular, an open drive tube sampler with 132 mm diameter, designed at TUT, was used to collect high quality samples. For comparison, samples were also taken using the conventional piston samplers and Sherbrooke Mini-block sampler. Field testing included piezocone, vane shear, and seismic piezocone. Laboratory testing consisted of index, consolidation, triaxial and simple shear tests. A comprehensive study of all these data is presented in a framework to describe Perniö soft clay.publishedVersio
Advantages and limitation of using 2-D FE modelling for assessment of effect of mitigation measures for railway vibrations
Get PDFThis paper addresses mitigation measures against railway vibrations in soft soils by use of FE calculations. In order for calculation models to be used as design tools, it is essential that they are relatively easy to set up and have reasonably short computational times which would allow sensitivity and optimization analyses. It is therefore desirable to use two-dimensional (2D) models to the greatest possible extent. The focus of this paper is to investigate the advantages and limitation of using such models as engineering approach to study effect of countermeasures. The difference between 2D and three-dimensional (3D) calculation models, and the performance of absorbing boundary conditions are investigated. The study shows that 2D models provide satisfactory results as long as root mean square values are considered, the treated area is long compared to other relevant distances, and the results are primarily used to compare different mitigation measures. However, since geometrical attenuation is not correctly captured in 2D models, they should not be used to calculate absolute vibration values. In a presented case study, the effects of lime-cement columns under the track bed and as a vibration-reducing screen parallel to the track are calculated and compared. The study shows good effect of both mitigation measures in the low frequency range. To avoid structure-borne noise problems, it may be necessary to combine columns below track bed with mitigation measures effective at higher frequencies, such as rail pads or ballast mats
Using local monitoring data for regional forecasting of weather-induced landslides in Norway
Get PDFSince 2013, a national early warning system addressing weather-induced landslides in soils is operational in Norway. The system is based on real-time hydro-meteorological measurements used as input to a spatially distributed precipitation-runoff model covering the whole country with 1 km by 1 km grid. The warning thresholds are defined considering relative water supply and relative groundwater conditions. This study presents a methodology aiming at integrating the adopted warning model with monitoring data collected at local scale, specifically pore water pressure measurements. Preliminary analyses of the temporal and spatial distribution of the landslide events in relation to the modelled territorial data and the local monitoring data are conducted within a test area, highlighting the additional contribution of local measurements for early warning purposes. The results of the research may be considered as a first attempt to integrate regional and local monitoring data within a warning model for landslides.Using local monitoring data for regional forecasting of weather-induced landslides in NorwaypublishedVersio
Decision-Based Approach to Account for Uncertainty in Estimating the Overtopping Hazard to Manage Risk for Dams
Get PDFThis paper describes and demonstrates an approach to improve the management of risks from small-probability events that can lead to large consequences. It applies a decision-based theory to account for limited information in estimating frequencies for rare events to large rockfill dam in Norway that is being assessed for rehabilitation. Uncertainties are considered specifically in estimating the overtopping hazard for the existing dam and for an elevated dam crest. Uncertainty in the estimates of the overtopping hazard curve means that smaller costs of dam failure and/or larger costs of rehabilitation may be justified. From a practical perspective, a cost of rehabilitation in this case that is nearly ten times larger could be justified when the uncertainty in the estimate of the hazard curve is considered. The value of perfect information about the hazard curve increases as the amount of information available decreases and as the cost of failure relative to the cost of rehabilitation decreases. In this case, the value of perfect information about the hazard curve is about 25 percent of the cost to raise the dam crestpublishedVersio
Constraints on Entrainment and Deposition Models in Avalanche Simulations from High-Resolution Radar Data
Get PDFDepth-integrated simulations of snow avalanches have become a central part of risk analysis and mitigation. However, the common practice of applying different model parameters to mimic different avalanches is unsatisfying. In here, we analyse this issue in terms of two differently sized avalanches from the full-scale avalanche test-site Vallée de la Sionne, Switzerland. We perform depth-integrated simulations with the toolkit OpenFOAM, simulating both events with the same set of model parameters. Simulation results are validated with high-resolution position data from the GEODAR radar. Rather than conducting extensive post-processing to match radar data to the output of the simulations, we generate synthetic flow signatures inside the flow model. The synthetic radar data can be directly compared with the GEODAR measurements. The comparison reveals weaknesses of the model, generally at the tail and specifically by overestimating the runout of the smaller event. Both issues are addressed by explicitly considering deposition processes in the depth-integrated model. The new deposition model significantly improves the simulation of the small avalanche, making it starve in the steep middle part of the slope. Furthermore, the deposition model enables more accurate simulations of deposition patterns and volumes and the simulation of avalanche series that are influenced by previous depositspublishedVersio
Investigation of chemical release and biota on seabed test fields in Grenlandsfjordene 2018-2019
No full textDenne rapporten beskriver overvåking av spredning og biotilgjengelighet av dioksiner (PCDD/F), heksaklorbenzen (HCB) og oktaklorstyren (OCS) i de ni årene fra etablering av testfelt for tynnsjikt-tildekking i Grenlandsfjordene i 2009, til siste store undersøkelse høsten 2018. Spredningen ble undersøkt in situ ved måling av utlekking med passive prøvetakere i bentiske kammer og ex situ i boks-kjerneprøver ved Marin Forskningsstasjon Solbergstrand. Bioakkumulering ble undersøkt i to sedimentlevende typer av organismer med forskjellig levevis og opptaksmekanismer. Selve tynnsjikthabitatene og utviklingen over tid har vært undersøkt ved utstrakt bruk av SPI-kamera og full makrofauna-kartlegging 1, 14, 48 og 110 måneder etter utlegging av tildekkingsmasser. Eksperimentet har vist at den ønskede effekten av tynnsjikttildekking med mineralske masser uten tilsatt aktivt kull i form av reduksjon i utlekking og biotilgjengelighet, opphørte 1-2 år etter utlegging. Med aktivt kull har både utlekking og opptak i organismer vært 60-90% lavere enn på ubehandlede referansefelt i hele perioden etter utlegging. Eksperimentet har avdekket et dilemma ved at bruken av aktivt kull har hatt en negativ effekt på faunasamfunnet som har vedvart minst ni år på et av feltene. Dersom metoden skal anvendes over et større område, må risikoen for skader på bunnfaunaen veies opp mot gevinsten ved redusert spredning og biotilgjengelighet av miljøgifter.Six test fields for thin layer capping were established in the Grenland fjords in 2009. The purpose was to test the suitability of this method to reduce the spread and bioavailability of dioxins from historically contaminated sediments. Classified according to Norwegian guidelines, the sediments in Ormerfjorden were "heavily polluted" (class IV) with dioxins, while the sediments in Eidangerfjorden were "very heavily polluted" (class V). The fields were established in the Ormerfjord (about 30 m deep) and the Eidangerfjord (about 100 m deep). Two fields were treated with suction dredged marine clay with activated carbon (AC), one field was treated with the same clay without AC and one field was treated with crushed rock (<2mm) from a limestone quarry on Langøya in the Oslofjord. In each of the fjords, a nearby, untreated reference field was established.publishedVersio