| 1. |
- Malehmir, Alireza, et al.
(författare)
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A multidisciplinary geophysical and geotechnical investigation of quick clay landslides in Sweden
- 2013
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Konferensbidrag (refereegranskat)abstract
- Landslides are one of the most commonly occurring naturaldisasters. They claim hundreds of human lives and costbillions of dollars every year. In order to providegeophysical tools and techniques to better characterize sitesprone to slide, we have been carrying out and evaluatingpotential utility of several geophysical surveys over a quickclay landslide site in southwest Sweden since 2011. Themeasurements include 2D and 3D P- and S-wave highresolution surface seismics, radio- and controlled-sourceelectromagnetics, geoelectrics, ground gravity andmagnetic surveys. A particular focus here is given to theseismic studies in the site. Combined with downholegeophysical and geotechnical measurements, we show thatmajority of reflections correlate well with sandy-siltyformations in the site. Quick clays often occur above theseformations, which may be an indication of the role ofcoarse-grained formations to not only partly form quickclays but also triggering them when pore-water pressure issignificantly increased.
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| 2. |
- Salas Romero, Silvia, et al.
(författare)
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Analysis of seismic data and correlation with downhole geophysical measurements in theassessment of a Swedish area prone to quick clay landslides
- 2013
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Konferensbidrag (refereegranskat)abstract
- The use of geophysics in the investigation of quick claylandslides in Sweden allows to obtain information about thepresence, and possibly even the origin of these kinds ofclays and their physical properties. Geophysical methodsare non-invasive and non-destructive, and if complementedby, for example, geotechnical and hydrologicalinvestigations, can allow a better and improvedcharacterization of the target area.Downhole geophysical measurements such as naturalgamma density, fluid conductivity, fluid temperature and apreliminary classification of the samples from threeboreholes are presented here from our GeoscientistsWithout Borders project in southwestern Sweden. Themeasurements allow not only the constraining of the originof reflections in nearby seismic lines, but also improve ourunderstanding about the way quick clay landslides function.This knowledge contributes significantly to quick claylandslide assessments and mitigating the risks associatedwith them.
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| 3. |
- Salas Romero, Silvia, et al.
(författare)
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Blind testing using seismic methods for detecting flaws in an experimental embankment dam in Älvkarleby, Sweden
- 2020
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Ingår i: Conference Proceedings, NSG2020 26th European Meeting of Environmental and Engineering Geophysics, Dec 2020, Volume 2020, p.1 - 5. - : European Association of Geoscientists & Engineers.
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Konferensbidrag (refereegranskat)abstract
- One of the most common failures in embankment dams is internal erosion of the body and in the foundation. Vattenfall leads a joint research project for assessing the potential of geophysical methods for detecting flaws (with unknown position and size) within the core of an experimental dam in Älvkarleby, Sweden. Equipment for measuring seismic, resistivity and temperature data were installed within the core at different depths and in other areas of the dam. In this study, seismic investigations, such as P-wave reflection seismic and P-wave traveltime tomography, focused on testing and, if possible, detecting the built-in flaws in an early stage before water filling the dam. The reflection seismic results for the top middle and upstream hydrophone lines show high resolution in the first meters of the sections. Repetition of the seismic surveys every two months may improve the identification of the defects and provide a time-lapse seismic study. Synthetic traveltime tomography results indicate the defect position, but fail in recovering its P-wave velocity and size. Acquiring seismic data once the dam reservoir is filled will provide more insights about the potential of this method.
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| 4. |
- Salas-Romero, Silvia, et al.
(författare)
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Combined land and river high-resolution reflection seismic imaging of an area prone to quick-clay landslides in Sweden
- 2016
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Konferensbidrag (refereegranskat)abstract
- Quick-clay landslides are common in northern countries and the delineation of these materials is important when planning urban areas. High-resolution reflection seismic data were acquired on land along four profiles in an area prone to quick-clay landslides in southwest Sweden in 2013. These data complement previous investigations that show the influence of the underlying coarse-grained layers in the formation and thickness of the quick clays. The intercalation of the different glacial and postglacial sediments, and the structural information of the subsurface provide clues to the possible causes of a landslide. Apart from the land data, river seismic data, using one and six channels, were obtained. All the seismic sections show a clear undulating bedrock reflection, and signs of bedrock faults at shallower depth that maybe important in the generation of quick clays and landslides. The coarse-grained layer reflection is delineated on the land data, and several filled channels can be distinguished along the river. The presence of the coarse-grained layer indicates the possible large extension of the quick clays in the study area, which needs to be confirmed using geotechnical investigations.
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| 5. |
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| 6. |
- Salas-Romero, Silvia, et al.
(författare)
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Geotechnical site characterization using multichannel analysis of surface waves : A case study of an area prone to quick-clay landslides in southwest Sweden
- 2021
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Ingår i: Near Surface Geophysics. - : John Wiley & Sons. - 1569-4445 .- 1873-0604. ; 19:6, s. 699-715
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Tidskriftsartikel (refereegranskat)abstract
- Quick-clay landslides are important geohazards in Sweden, Norway and Canada. While they have been studied using various geotechnical and geophysical methods, only a handful of seismic surveys have been reported for their studies. Here, we reprocess active-source seismic data from a quick-clay landslide site in southwest Sweden to complement earlier studies of reflection imaging and first-break traveltime tomography with surface-wave dispersion analysis. Results suggest extremely low shear-wave velocities, even as low as 60–100 m/s. From a geotechnical perspective, this implies that the region classifies as a high-risk zone for landslides and construction purposes. High or anomalous values of Poisson's ratio (or similarly P- and S-wave velocity ratio) depict a zone within the normally consolidated sediments that likely represents a coarse-grained layer, thus confirming earlier results from a number of boreholes drilled in the study area. Overall, the results presented further support to the previous hypothesis that the coarse-grained layer plays a major role in the formation and creation of quick-clay landslides in the study area. Additionally, an attempt to model the distribution of potential quick clays along one of the seismic profiles is performed through a combination of the modelled geophysical properties and soil textures. This study illustrates the potential of seismic methods, and how the integration of multiple geophysical properties and different data handling strategies can help to accurately characterize regions susceptible to quick-clay landslides.
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| 7. |
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| 8. |
- Salas-Romero, Silvia, et al.
(författare)
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Identifying landslide preconditions in Swedish quick clays—insights from integration of surface geophysical, core sample- and downhole property measurements
- 2016
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Ingår i: Landslides. - : Springer Science and Business Media LLC. - 1612-510X .- 1612-5118. ; 13:5, s. 905-923
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Tidskriftsartikel (refereegranskat)abstract
- Quick-clay landslides are a serious geohazard in Canada, Norway and Sweden. Identification and mapping of quick clays are essential endeavours because the damage caused by an individual landslide can be large and costly, with potentially fatal consequences. We collected geophysical borehole and soil core data from an area prone to quick-clay landslides in southwestern Sweden. Methodologies included in situ and laboratory measurements, providing information about natural gamma radiation, sonic velocities, electrical conductivity, pH, physical grain size, elemental and mineral composition, magnetic properties, cation exchange capacity and fossil content. A stratigraphic thickness of almost 60 m enables us to study quick clays and their host environment in Sweden at unusually high resolution. Results identify the origin and location of reflections in nearby seismic lines and assign physico-chemical properties to the geological units present in the area. We show that coarse-grained layers are sandwiched between marine clays (some of which are quick clays). These layers function as a conduit for relatively fresh water that infiltrates the marine clays and chemically destabilizes them by leaching out their salts. The salinity distribution in the boreholes indicate that the groundwater movement is downwards, through the coarse-grained layer and towards the Göta river. The presence of these materials is important for the development of quick clays, although not a prerequisite. With the help of surface geophysical methods, the location of the coarse-grained layers can be known faster and more economically, which could be relevant for studying the potential for quick-clay landslide occurrence over large areas.
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| 9. |
- Salas Romero, Silvia
(författare)
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Multidisciplinary Near-Surface Investigation of a Quick-Clay Landslide Prone Area in Southwest Sweden
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Quick-clay landslides are considered one of the most important geohazards in Sweden, Norway, and Canada. The deposits involved are glacial and postglacial clays and silty clays, which are very sensitive to increased stress that may collapse their structure and cause liquefaction.A multidisciplinary approach was adopted in this study of quick clays in an area of southwest Sweden that is prone to landslides. It was mainly based on geophysical methods, but was complemented and validated with geotechnical, geological, and hydrological data. Downhole geophysics, land and river reflection seismics, radio magnetotellurics, P-wave refraction tomography, magnetics, and multichannel analysis of surface waves comprised the main geophysical methods used in this research. Laboratory measurements of core samples, such as grain size analysis, mineral magnetic properties, fossil content, X-ray fluorescence, cation exchange capacity, X-ray powder diffraction, electrical conductivity, and pH were also taken. Hydrological modelling was used to obtain information on the properties of groundwater within a coarse-grained layer, given the importance of this information in the formation of quick clays.The evaluation of the physico-chemical properties of the coarse-grained layer revealed high values of magnetic susceptibility, probably as a result of fluvial sorting, which tends to accumulate denser minerals such as magnetite. Potential quick clays were visually observed above this layer, and their presence was also confirmed by geotechnical data acquired in previous studies. Marine fossils identified within the coarse-grained layer confirmed the glaciomarine origin of the clays. Geophysical results revealed the presence of large-scale structures, an undulating fractured bedrock and a coarse-grained layer sandwiched between clay deposits, with leached sediments on top and unleached sediments below. This layer, important for the development of quick clays in the area, was 3D modelled in a regional context. Magnetic data also revealed that the coarse-grained layer together with quick clays, have the potential to act as a sliding prone layer. Multichannel analysis of surface waves helped to geotechnically characterize the area. Although the results could not reach the deeper layers, it did yield information about the shallower layers of clay, silt and sand. The VS30 values indicated the presence of soft soils, as well as soft clays/silts with high plasticity index and high water content.This PhD is expected to improve the current knowledge of quick-clay landslides and how they are preconditioned. Climate change will probably affect the study area in the near future, most likely increasing landslide risk, therefore, research should continue and advance to new levels. Application of other geophysical methods such as borehole or geophysical monitoring, and induced polarization, could provide more information about the formation of quick clays and associated landslides.
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| 10. |
- Salas Romero, Silvia, et al.
(författare)
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Subsurface characterization of a quick-clay vulnerable area using near-surface geophysics and hydrological modelling
- 2019
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Ingår i: Solid Earth. - : Copernicus GmbH. - 1869-9510 .- 1869-9529. ; 10:5, s. 1685-1705
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Tidskriftsartikel (refereegranskat)abstract
- Quick-clay landslides are common geohazards in Nordic countries and Canada. The presence of potential quick clays is confirmed using geotechnical investigations, but near-surface geophysical methods, such as seismic and resistivity surveys, can also help identify coarse-grained materials associated with the development of quick clays. We present the results of reflection seismic investigations on land and in part of the Gota River in Sweden, along which many quick-clay landslide scars exist. This is the first time that such a large-scale reflection seismic investigation has been carried out to study the subsurface structures associated with quick-clay landslides. The results also show a reasonable correlation with radio magnetotelluric and travel-time tomography models of the subsurface. Other ground geophysical data, such as high magnetic values, suggest a positive correlation with an increased thickness of the coarse-grained layer and shallower depths to the top of the bedrock and the top of the coarse-grained layer. The morphology of the river bottom and riverbanks, e.g. subaquatic landslide deposits, is shown by side-scan sonar and bathymetric data. Undulating bedrock, covered by subhorizontal sedimentary glacial and postglacial deposits, is clearly revealed. An extensive coarse-grained layer (P-wave velocity mostly between 1500 and 2500 m s(-1) and resistivity from approximately 80 to 100 Omega m) exists within the sediments and is interpreted and modelled in a regional context. Several fracture zones are identified within the bedrock. Hydrological modelling of the coarse-grained layer confirms its potential for transporting fresh water infiltrated in fractures and nearby outcrops located in the central part of the study area. The modelled groundwater flow in this layer promotes the leaching of marine salts from the overlying clays by seasonal inflow-outflow cycles and/or diffusion, which contributes to the formation of potential quick clays.
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| 11. |
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