Norwegian Geotechnical Institute (NGI) Digital Archive
Not a member yet
1356 research outputs found
Sort by
Impact of cone penetrometer type on measured CPTU parameters at 4 NGTS sites. Silt, soft clay, sand and quick clay
Get PDFUsing cone penetrometers from different manufacturers may yield different results even if the equipment complies with international standards. This report presents a study on differences in CPTU test results as function of cone type.
The Norwegian GeoTest Sites (NGTS) project established five research sites with different characteristic soil types in 2016. This study includes testing at four of the NGTS sites, i.e. soft clay site, silt site, quick clay site and sand site, using twelve different penetrometers from five manufacturers. In total, eighty-seven cone penetration tests are evaluated.
A major contributor to the scatter in CPTU results appear to be the temperature at which zero readings were taken. It was decided to do a temperature correction of all the results. This significantly decreased the scatter in the data. To eliminate this uncertainty, it is recommended to take zero readings with the cone penetrometer at a temperature as close as possible to ground temperature as recommended by ISO 22476-1:2012. If this is not the case, it is recommended to use cone specific temperature calibration to correct for temperature effects.
Regarding tests with the same cone type, this study suggests that the penetration pore pressure, u2, provides the most repeatable results. The corrected cone resistance, qt, generally varies somewhat more than u2. Some of the cone types give good repeatability for sleeve friction, fs, while some show relatively large variation. These conclusions are valid for all test sites. Comparing results from different cone types reveal that the penetration pore pressure generally produces less scatter compared to the corrected cone resistance and sleeve friction. The measured sleeve frictions are very small for soft soils and vary significantly from one cone type to another, which is in line with previous experience. Hence one should be careful using sleeve friction, and the friction ratio, when interpreting soil parameters for design in soft soils. Since the measured u2 appears to be the most reliable parameter, it should be used in addition to qt for deriving soil parameters.
The results show that filter saturation is poor in the start of some tests and this could be improved as emphasized by ISO 22476-1:2012. Following the ISO code it is recommended to carry out the testing with a minimum distance between a CPT and adjacent boreholes of 2 m. The thrust machine should push the rods so that the axis of the pushing force is as close to vertical as possible. The deviation from the intended axis of the cone should be less than 2°.
For some of the tests at the soft clay sites, measured sleeve friction, not corrected for temperature, can be as low as zero. For subtraction cones, the measured values may be this low due to the way the sleeve friction is calculated. A small offset in the measured cone resistance may lead to erroneous values of sleeve friction. As remedy it is suggested to correct the cone resistance and resistance behind sleeve for temperature effects before doing the subtraction.
Some cone penetrometers are sensitive to temperature changes and it was decided to study the time necessary to get stabile readings of the cone resistance, sleeve friction and penetration pore pressure at zero load level. The penetrometers were placed in a bucket of water and in free air. The results show the importance of good procedures for taking zero readings and indicate that cone temperature may seriously affect the readings. The importance of waiting for the readings to stabilize at ground temperature is evident from the results. It was also observed that stabilization is quicker and more uniform when taking readings in water compared to taking readings in air. A procedure for taking stable zero readings close to ground temperature has been suggested.publishedVersio
Coupling rheology and segregation in granular flows
Get PDFDuring the last fifteen years there has been a paradigm shift in the continuum modelling of granular materials; most notably with the development of rheological models, such as the μ(I) μ(I) -rheology (where μ μ is the friction and I is the inertial number), but also with significant advances in theories for particle segregation. This paper details theoretical and numerical frameworks (based on OpenFOAM) which unify these currently disconnected endeavours. Coupling the segregation with the flow, and vice versa, is not only vital for a complete theory of granular materials, but is also beneficial for developing numerical methods to handle evolving free surfaces. This general approach is based on the partially regularized incompressible μ(I) μ(I) -rheology, which is coupled to the gravity-driven segregation theory of Gray & Ancey (J. Fluid Mech., vol. 678, 2011, pp. 353–588). These advection–diffusion–segregation equations describe the evolving concentrations of the constituents, which then couple back to the variable viscosity in the incompressible Navier–Stokes equations. A novel feature of this approach is that any number of differently sized phases may be included, which may have disparate frictional properties. Further inclusion of an excess air phase, which segregates away from the granular material, then allows the complex evolution of the free surface to be captured simultaneously. Three primary coupling mechanisms are identified: (i) advection of the particle concentrations by the bulk velocity, (ii) feedback of the particle-size and/or frictional properties on the bulk flow field and (iii) influence of the shear rate, pressure, gravity, particle size and particle-size ratio on the locally evolving segregation and diffusion rates. The numerical method is extensively tested in one-way coupled computations, before the fully coupled model is compared with the discrete element method simulations of Tripathi & Khakhar (Phys. Fluids, vol. 23, 2011, 113302) and used to compute the petal-like segregation pattern that spontaneously develops in a square rotating drum.publishedVersio
Stabilization of PFAS-contaminated soil with activated biochar
Get PDFBiochars are considered potential sustainable sorbents to reduce the leaching of per- and polyfluoroalkyl substances (PFAS) fromcontaminated soils. However, biochar characteristicsmust probably be optimized to achieve useful sorption capacity. In the presentwork, eightwaste timber biochars were produced, including biochars activated to different degrees, at different temperatures, and using both steamand CO2. In laboratory batch experiments, the eight biochars were amended to soil samples from two different horizons, with low and high total organic carbon (TOC, 1.6% and 34.2%, respectively), of a heavily PFAS-contaminated soil (1200–3800 μg kg−1 PFAStot), at varying doses (0, 0.1, 0.5, 1.0 and 5.0%).With a 5% amendment to the low-TOC soil, all eight biochars resulted in strongly reduced leachate PFAS concentrations (by 98–100%). At the same amendment dose in the high-TOC soil, leachate concentration reductions were more modest (23–100%). This was likely due to a strong PFAS-sorption to the high-TOC soil itself, as well as biochar pore clogging in the presence of abundant organic matter, resulting in fewer sorption sites available to PFAS. Reduction in PFAS leachingwas proportional to the degree of activation and activation temperature. Thus, lower amendment doses of activated biochars were needed to reduce PFAS leaching to the same level as with the non-activated biochar. Activation however, came at a tradeoff with biochar yield. Furthermore, the adsorption ability of these biochars increased proportionally with PFAS-fluorocarbon chain length, demonstrating the role of hydrophobic interactions in reduction of PFAS leaching. Development of internal surface area and porosity was proposed as the main factor causing the improved performance of activated biochars. This study shows that woody residues such as waste timber can be used to produce effective sorbents for the remediation of PFAS-contaminated soil. It also highlights the desirability of sorbate and matrix-specific optimization of biochar production.publishedVersio
Paper product production identified as the main source of per- and polyfluoroalkyl substances (PFAS) in a Norwegian lake: Source and historic emission tracking
Get PDFThe entirety of the sediment bed in lake Tyrifjorden, Norway, is contaminated by per- and polyfluoroalkyl substances (PFAS). A factory producing paper products and a fire station were investigated as possible sources. Fire station emissions were dominated by the eight carbon perfluoroalkyl sulfonic acid (PFSA), perfluorooctanesulfonic acid (PFOS), from aqueous film forming foams. Factory emissions contained PFOS, PFOS precursors (preFOS and SAmPAP), long chained fluorotelomer sulfonates (FTS), and perfluoroalkyl carboxylic acids (PFCA). Concentrations and profiles in sediments and biota indicated that emissions originating from the factory were the main source of pollution in the lake, while no clear indication of fire station emissions was found. Ratios of linear-to branched-PFOS increased with distance from the factory, indicating that isomer profiles can be used to trace a point source. A dated sediment core contained higher concentrations in older sediments and indicated that two different PFAS products have been used at the factory, referred to here as Scotchban and FTS mixture. Modelling, based on the sediment concentrations, indicated that 42e189 tons Scotchban, and 2.4e15.6 tons FTS mixture, were emitted. Production of paper products may be a major PFAS point source, that has generally been overlooked. It is hypothesized that paper fibres released from such facilities are important vectors for PFAS transport in the aquatic environment.publishedVersio
Wind simulations for use in local avalanche forecasting
Get PDFQuantification of release probabilities in local avalanche forecasting are depending on
knowledge of historical weather characteristics as well as detailed knowledge of the
wind driven snow distribution on a fine scale. In WP5 we have computed extreme
weather statistics for snow and other related parameters for historical and future climates
at 1 km2 resolution (2), and prepared gridded regional scale wind data for use in statistics
together with historical gridded data (3). Within each 1x1 km grid cell wind is the
dominant factor determining snow distribution in the terrain. Simple terrain indexes as
well as a complex fluid dynamic (CFD) model have been tested and evaluated with
respect to performance in modelling wind fields (4), determine snow distribution (4.7)
and potential release areas (4.8). Several scripts and tools have been developed along
this study with the aim of establishing an improved toolbox for avalanche forecasting
on a local scale.Norges vassdrags- og energidirektora
Deliverable 3.3. Reports on execution of field trails at each case study site
Get PDFThe main objective of the field trials was to bring into practice the key aspects of EVOKED: the focus on climate services, the Living Labs approach, and the information design of the selected climate services for each of the EVOKED case study sites (Deltares, 2019). To support comparing the outcomes of these case studies, Deliverable 3.2 (Deltares, 2020) was developed to create a framework to structure the data that has been collected in the case studies as well as to draw lessons and conclusions based on a case comparison. The final objective as presented in the present report is “a systematic evaluation of the climate information designs and thus of the communicative qualities of currently used climate services; insight into the different information needs, perceptions of risk and uncertainty, and the responsibilities and roles of different stakeholder groups; a set of visualization principles and visualization strategies for stakeholder specific climate services.” (Deltares, 2019, p.17).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
Evaluation of soil models for improved design of offshore wind turbine foundations in dense sand
Get PDFIn order to perform optimised and safe design of foundations for offshore wind turbines (OWT), it is important to have calculation tools that describe the key features of water-saturated soil subjected to complex and irregular loading over a wide range of strain levels. Soils subjected to cyclic loading are prone to strain accumulation. The accumulated (plastic) volumetric strain may result in excess pore pressure or stress relaxation, which will reduce the effective stresses, stiffness and strength of the material. Strain accumulation in dense sand is a complex mechanism of deformation and it is challenging to describe it properly. Four different soil models to describe the stress–strain relationships of dense sand are evaluated in this paper: two implicit models that follow the actual stress history and two explicit models that calculate the accumulated strains as a function of number of cycles. These models are first evaluated on the basis of their theoretical framework and back-calculations of laboratory tests specifically carried out for the design of OWT foundations in dense sand. Second, the models are implemented in finite-element analyses and evaluated on the basis of the analyses of an OWT monopile subjected to different loading conditions.publishedVersio
Wetting-Drying Response of an Unsaturated Pyroclastic Soil Vegetated with Long-Root Grass
Get PDFThis paper investigates the effect of a long-root grass on the hydraulic response of a partially saturated pyroclastic soil. The work is based on both long-term monitoring under atmospheric conditions and short-term wetting/drying tests, aimed to simulate rainfall/evapotranspiration during different seasons. A 1D physical model was created, namely two identical columns were filled with a pyroclastic silty-sand, and later equipped with tensiometers and soil moisture sensors at four depths. One column was vegetated, while the second was left bare as a control. Roots growth and foliage evolution were observed for one year. The monitoring of the hydraulic variables highlighted the capability of vegetation to modify the retention ability of the rooted soil. During the drying tests, the final soil suction within the rooted zone was higher than in the bare soil, especially during summer, when plant transpiration is very high. In the wetting tests, the presence of vegetation delayed the infiltration process, reducing the total amount of water infiltrating the soil, and consequently the chances for rainfall to cause a drop in soil suction. The paper quantifies the effects of long-rooted grass, here conceived as a nature-based solution viable in landslide prone areas.acceptedVersio
Hydrogeological characterization of an alpine aquifer system in the Canadian Rocky Mountains
Get PDFGroundwater storage in alpine regions is essential for maintaining baseflows in mountain streams. Recent studies have shown that common alpine landforms (e.g., talus and moraine) have substantial groundwater storage capacity, but the hydrogeological connectivity between individual landforms has not been understood. This study characterizes the hydrogeology of an alpine cirque basin in the Canadian RockyMountains that contains typical alpine landforms (talus,meadow, moraines) and hydrological features (tarn, streams, and springs). Geological, hydrological, and hydrochemical observations were used to understand the overall hydrogeological setting of the study basin, and three different geophysical methods (electrical resistivity tomography, seismic refraction tomography, and ground penetrating radar) were used to characterize the subsurface structure and connectivity, and to develop a hydrogeological conceptual model. Geophysical imaging shows that the talus is typically 20–40 m thick and highly heterogeneous. The meadow sediments are only up to 11 m thick but are part of a 30–40-m-thick accumulation of unconsolidated material that fills a bedrock overdeepening (i.e. a closed, subglacial basin). A minor, shallow groundwater system feeds springs on the talus and streams on the meadow, whereas a deep system in the moraine supplies most of the water to the basin outlet springs, thereby serving as a ‘gate keeper’ of the basin.Although the hydrologic functions of the talus in this study are substantially different from other locations, primarily due to differences in bedrock lithology and geomorphic processes, the general conceptual framework developed in this study is expected to be applicable to other alpine regionspublishedVersio