Multi‐method geophysical mapping of quick clay

Abstract

The UCD community has made this article openly available. Please share how this access benefits you. Your story matters! (@ucd_oa) Some rights reserved. For more information, please see the item record link above. ABSTRACT Marine clay deposits in coastal, post-submarine areas of Scandinavia and North America may be subjected to quick clay landslides and hence significant efforts are being taken to map their occurrence and extent. The purpose of this paper is to assess the use of a number of geophysical techniques for identifying quick clay. The investigated area, Smørgrav, located in southern Norway has a history of quick clay sliding, the most recent event occurring in 1984. Geophysical techniques that are used include electromagnetic conductivity mapping, electrical resistivity tomography, seismic refraction and multichannel analysis of surface waves. These results are compared to geotechnical data from bore samples, rotary pressure soundings and cone penetration testing. A number of these approaches have proved promising for identifying quick clay, in particular electrical resistivity tomography and electromagnetics, which delineated a zone of quick clay that had previously been confirmed by rotary pressure soundings and sampling. Seismic refraction was useful for determining the sediment distribution as well as for indicating the presence of shallow bedrock whereas the multichannel analysis of surface-waves approach suggested differences between the intact stiffness of quick and unleached clay. It is observed that quick clay investigations using discrete rotary pressure soundings can be significantly enhanced by using, in particular, electrical resistivity tomography profiles to link together the information between test locations, perhaps significantly reducing the need for large numbers of soundings.

Towards geophysical and geotechnical integration for quick‐clay mapping in Norway

“…) and geotechnical soundings (Moholdt ), resistivity values ranging from at this site mainly represent leached clay sediments and high‐resistivity values correspond to coarse sediments. This is in agreement with previous works (Solberg et al , 2011; Long et al ). Resistivity values below are not observed, suggesting that most of the clay has been leached, at least in the vicinity of the two ERT profiles.…”

Mapping of quick clay using geoelectrical imaging and CPTU‐resistivity

“…The potential for using electrical imaging for delineating areas with potential quick clay was demonstrated in the study presented by Rankka et al () and Lundström et al (). These results are supported by results presented by Solberg et al () and Donohue et al (). The above experiences have resulted in a Norwegian guideline for the use of electrical imaging for potential quick clay areas (Solberg et al ).…”

Assessment of near-surface mapping capabilities by airborne transient electromagnetic data — An extensive comparison to conventional borehole data

“…Review papers by Dahlin (2001) for direct current (DC) methods and Tekzan (1999) and Everett (2012) for induction EM methods provide overviews of the large range of applications in which near-surface geologic information is useful. Among the most recent studies, one can find various applications such as aquifer vul-nerability mapping (Röttger et al, 2005), landslide hazards (Pfaffhuber et al, 2010;Supper et al, 2013), clay mapping (Donohue et al, 2012), agriculture regulation (Refsgaard et al, 2014), and overburden mapping Oluwafemi and Oladunjoye, 2013). Most of those studies rely on the mapping of clay geologic units because of their particular mechanical and hydraulic properties, which play key roles in geotechnical (e.g., landslides, construction) and hydrogeological (e.g., groundwater flow modeling, pollution plumes) problems.…”