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Multidisciplinary Near-Surface Investigation of a Quick-Clay Landslide Prone Area in Southwest Sweden
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.ORCID iD: 0000-0002-7020-8769
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 70
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1775
Keywords [en]
Quick-clay, reflection seismic, landslide, southwest Sweden, borehole logging, physico-chemical properties, hydrogeological modelling, multichannel analysis of surface waves, magnetics
National Category
Geophysics Geosciences, Multidisciplinary Geology Environmental Sciences
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
URN: urn:nbn:se:uu:diva-375568ISBN: 978-91-513-0575-2 (print)OAI: oai:DiVA.org:uu-375568DiVA, id: diva2:1287343
Public defence
2019-03-29, Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2019-03-05 Created: 2019-02-11 Last updated: 2019-03-18
List of papers
1. Identifying landslide preconditions in Swedish quick clays - insights from integration of surface geophysical, core sample- and downhole property measurements
Open this publication in new window or tab >>Identifying landslide preconditions in Swedish quick clays - insights from integration of surface geophysical, core sample- and downhole property measurements
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2016 (English)In: Landslides: Journal of the International Consortium on Landslides, ISSN 1612-510X, E-ISSN 1612-5118, Vol. 13, no 5, p. 905-923Article in journal (Refereed) Published
Abstract [en]

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 Gota 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.

Keywords
Landslide; Quick clay; Southwestern Sweden; Correlation; Downhole geophysics; Physico-chemical properties
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-270198 (URN)10.1007/s10346-015-0633-y (DOI)000385174600005 ()
Funder
Swedish Research Council Formas
Note

Erratum in Landslides 13(5) pg: 1319 DOI: 10.1007/s10346-015-0653-7

Available from: 2015-12-22 Created: 2015-12-22 Last updated: 2019-02-11Bibliographically approved
2. Subsurface Structures of a Quick-Clay Sliding Prone Area Revealed Using Land-River Reflection Seismic Data and Hydrogeological Modelling
Open this publication in new window or tab >>Subsurface Structures of a Quick-Clay Sliding Prone Area Revealed Using Land-River Reflection Seismic Data and Hydrogeological Modelling
(English)In: Solid Earth, ISSN 1869-9510, E-ISSN 1869-9529Article in journal (Other academic) Submitted
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-375560 (URN)
Available from: 2019-02-07 Created: 2019-02-07 Last updated: 2019-02-11
3. Geotechnical Site Characterization Using Multichannel Analysis of Surface Waveṣ–A Case Study of an Area Prone to Quick-Clay Landslides in Southwest Sweden
Open this publication in new window or tab >>Geotechnical Site Characterization Using Multichannel Analysis of Surface Waveṣ–A Case Study of an Area Prone to Quick-Clay Landslides in Southwest Sweden
(English)Manuscript (preprint) (Other academic)
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-375563 (URN)
Available from: 2019-02-10 Created: 2019-02-10 Last updated: 2019-02-19

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