Mapping of quick clay using geoelectrical imaging and CPTU‐resistivity

Abstract

Quick clay has a major impact on landslide risk and it is therefore of considerable interest to map its presence and extent. In Sweden, quick clay has been involved in most landslides in soft clay with serious consequences. The predominant method for detection of quick clay in Sweden has been to take undisturbed samples and to perform fall‐cone tests on the clay in its undisturbed and remoulded state. Originally deposited in saltwater in a marine environment, the salt maintains the stability of the clay. When the salt is leached out, the clay can become quick. When salt is leached from clay of marine origin the resistivity increases. In this study the intention was to calibrate electrical imaging with cone penetration tests with resistivity measurements (CPTU‐R) and measurement of the total penetration resistance, i.e. the total rod friction, together with both geotechnical and chemical analyses on specimens in the laboratory. The results show that electrical imaging can be used for separation of leached soil volumes in marine clays that may form quick clay, from those where the salt content remains too high for this. In the dry crust and thin weathered zone at the top, the resistivity is high but the clay is non‐quick. Also soils with less clay content will have higher resistivity without being quick. The technique may thus be used as a screening tool in order to delimit areas where further investigations are needed from areas that do not require more attention. This has a potential of saving significant resources if used in a relatively early stage of the survey process. It can also increase the overall quality and reliability of the survey results. The induced polarization (IP) results are consistent and seem to be geologically realistic, and appear to contain additional information to the resistivity that is related to material or electrochemical properties, although it is not clear how due to lack of sufficiently detailed reference data. The electrical imaging gives a general picture of the variation in resistivity along soil sections. The CPTU‐R gives variations at depth with very high vertical resolution in one specific location. There is generally good agreement between the models based on electrical imaging and the CPTU‐R. The CPTU‐R results may be used to calibrate the electrical imaging results with quick clay estimations based on rod friction.

Airborne mapping of sensitive clay—stretching the limits of AEM resolution and accuracy

“…In addition, groups in Sweden and Canada, where quick clay is commonly referred to as Leda or Champlain Sea clay, have studied the applicability of geophysical methods (Dahlin et al . ; Hunter et al . ; Shan et al .…”

Assessment of the Efficiency of Consolidation Treatment through Injections of Expanding Resins by Geotechnical Tests and 3D Electrical Resistivity Tomography

“…The 3D representation of subsurface resistivity distribution, associated with the information deriving from the geotechnical survey (penetrometric or other tests) allows an initial general classification of the soils. The effectiveness of combining these survey techniques was recently confirmed by Dahlin et al [ 26 ]. Moreover, the ERT provides details, regarding the type, continuity, and depth of the foundation, characterising any anomalies due to the presence of voids, water retention, or other distinctive lithological elements.…”

Geotechnical site characterization using multichannel analysis of surface waves: A case study of an area prone to quick‐clay landslides in southwest Sweden

“…Quick clays are clayey sensitive glacial and postglacial sediments that are prone to liquefaction under increased stress conditions, such as heavy rainfall, earthquakes or unloading/loading works (Osterman 1963;Torrance 2012). They have extensively been studied by geotechnical and resistivity methods (Dahlin et al 2013;Löfroth et al 2011;Lundström, Larsson and Dahlin 2009;Solberg et al 2012Solberg et al , 2016Wang, Malehmir and Bastani 2016), while only a few studies report the usage of surface-wave dispersion analysis for different investigations on quick clays (e.g. Comina et al 2017;Donohue et al 2012;Long, Wood and L'Heureux 2017;Sauvin et al 2013).…”

“…This area has been subjected to numerous geophysical, geotechnical and hydrological surveys (Fig. 1, Adamczyk et al 2013Adamczyk et al , 2014Comina et al 2017;Dahlin et al 2013;Malehmir et al 2013a, b;Löfroth et al 2011;Lundberg et al 2014;Polom et al 2013;Salas-Romero et al 2016, 2019Shan et al 2014Shan et al , 2016Wang et al 2016). The main target of these different investigations was mostly quick-clay mapping.…”