Delineation of a quick clay zone at Smørgrav, Norway, with electromagnetic methods under geotechnical constraints

Thomas Kalscheuer, Mehrdad Bastani, Shane Donohue, Lena Persson, Andreas Aspmo Pfaffhuber, Fabienne Reiser, Zhengyong Ren

    Research output: Contribution to journalArticle

    25 Citations (Scopus)
    335 Downloads (Pure)

    Abstract

    In many coastal areas of North America and Scandinavia, post-glacial clay sediments have emerged above sea level due to iso-static uplift. These clays are often destabilised by fresh water leaching and transformed to so-called quick clays as at the investigated area at Smørgrav, Norway. Slight mechanical disturbances of these materials may trigger landslides. Since the leaching increases the electrical resistivity of quick clay as compared to normal marine clay, the application of electromagnetic (EM) methods is of particular interest in the study of quick clay structures.

    For the first time, single and joint inversions of direct-current resistivity (DCR), radiomagnetotelluric (RMT) and controlled-source audiomagnetotelluric (CSAMT) data were applied to delineate a zone of quick clay. The resulting 2-D models of electrical resistivity correlate excellently with previously published data from a ground conductivity metre and resistivity logs from two resistivity cone penetration tests (RCPT) into marine clay and quick clay. The RCPT log into the central part of the quick clay identifies the electrical resistivity of the quick clay structure to lie between 10 and 80 O m. In combination with the 2-D inversion models, it becomes possible to delineate the vertical and horizontal extent of the quick clay zone. As compared to the inversions of single data sets, the joint inversion model exhibits sharper resistivity contrasts and its resistivity values are more characteristic of the expected geology. In our preferred joint inversion model, there is a clear demarcation between dry soil, marine clay, quick clay and bedrock, which consists of alum shale and limestone.
    Original languageEnglish
    Pages (from-to)121-136
    Number of pages16
    JournalJournal of Applied Geophysics
    Volume92
    DOIs
    Publication statusPublished - May 2013

    Bibliographical note

    The data presented in this paper were collected as part of NGI projects “SIP12 — Resistivity anisotropy in quick clay” in 2009 and “SIP12 — Procedures for quick clay mapping” in 2010 funded by the Research Council of Norway and the International Centre for Geohazards. Geotechnical and -chemical analyses at Smørgrav have been performed by Tonje Eide Helle, RCPT data were supplied by Magnus Romøen. Sara Bazin was involved in ERT data acquisition and processing in Smørgrav.

    ASJC Scopus subject areas

    • Geophysics

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