Geophysical assessment and geotechnical investigation of quick‐clay landslides – a Swedish case study

Abstract

We present a preliminary assessment of the potential utility of various geophysical measurements carried out over a quick-clay landslide site in south-west Sweden. The multidisciplinary approach includes active P-and S-wave seismic investigations, including 2D and 3D reflection and refraction surveys, passive single and 3C seismic surveys, electrical resistivity tomography and electromagnetic surveys including controlled-source and radio-magnetotellurics, ground-penetrating radar and potential field studies. The P-wave and particularly S-wave reflection seismic data show a highresolution image of bedrock topography and the stratigraphy of a 100 m thick sequence of sediments that lies on top, which include lightly consolidated quick-clays. Of particular interest is the identification of a layer of relatively coarse-grained material between 10-20 m below the ground surface. Geotechnical investigations indicate that most but not all quick-clays at the site are located above this layer. Further studies are required to determine the importance of their relationship and whether the coarse-grained layer may have had a role in triggering quick-clay landslides in the region. Geoelectrical and electromagnetic methods provide high-resolution images of the unconsolidated subsurface and particularly the normal and leached clays. Radio-magnetotelluric methods proved valuable near the river where traditional geoelectrical methods failed to provide sufficient depth coverage. The study shows that geophysical data are able to image major subsurface structures associated with quick-clay landslides.

Interlobate esker architecture and related hydrogeological features derived from a combination of high-resolution reflection seismics and refraction tomography, Virttaankangas, southwest Finland

“…500 m/s) in the first few meters below the land surface. When the sediments become saturated (below water table or its vicinity) the seismic velocity makes a large increase to 1,500-1,800 m/s, which is typical for sandy or silty sediments (e.g., Malehmir et al 2013a;Salas-Romero et al 2016). During the preparation of the seismic data, a clear reflection of about 500 m/s consistently appeared at shallow depths on most shot gathers after direct arrivals (see for example the top red arrow in Fig.…”

“…above water table) and another one was focused on the bedrock surface and the structures in its immediate vicinity. An approach tested before (Miller and Xia 1998;Juhlin et al 2010;Malehmir et al 2013a;Place et al 2015) was to combine two different sets of reflections, by generating a stack focusing on very shallow reflections and another one focusing on bedrock reflections or below the water table. This gave the best results for profile 1 where 10-20 m deep shallow structures could be identified.…”

Landslide investigations in the northwest section of the lesser Khingan range in China using combined HDR and GPR methods

“…These techniques, less invasive than direct ground-based techniques (i.e., drilling, inclinometer, laboratory tests), provide information integrated on a greater volume of the soil, thus overcoming the point-scale feature of classical geotechnical measurements. Among the in situ geophysical techniques, the high-density resistivity (HDR) and groundpenetrating radar (GPR) methods have been increasingly applied for landslide investigation (McCann and Forster 1990;Malehmir et al 2013;Timothy et al 2014).…”

Boat-towed radio-magnetotellurics — A new technique and case study from the city of Stockholm

“…There are a vast number of publications covering a wide range of hydrological (e.g., Rubin and Hubbard, 2005;Hördt et al, 2007;Slater, 2007), environmental (e.g., Bastani et al, 2012;Chen et al, 2013;Revil et al, 2013), and engineering applications including underground-construction studies (e.g., Danielsen and Dahlin, 2009;Malehmir et al, 2013Malehmir et al, , 2015. These mainly focus on land (or downhole) geophysical data acquisitions and interpretation.…”