Delineating Potential Quick-clay Areas Using High-resolution Seismic Methods: Towards a 3D Model of an Area Prone to Slide in SW Sweden

Abstract:

Quick clay can liquefy under increased stress and is responsible for major landslides in Sweden, Norway and Canada, but despite extensive investigations delineating quick clay remains a challenge. As part of a large multidisciplinary project, this study focuses on an area prone to quick-clay landslides in SW Sweden. P- and S-wave seismic, electrical resistivity tomography, and RMT (radio-magnetotelluric) data obtained in 2011 (Malehmir et al. 2013) suggested the presence of a coarse-grained layer of variable thickness sandwiched between clays, with quick clay above. The coarse-grained layer was assumed to accelerate the formation of quick clay, influencing its thickness. Additional geophysical data (reflection and refraction seismic, and RMT) and studies of three boreholes drilled in 2013, with the aim to intersect the coarse-grained layer, extended the area covered in 2011. Here we report on four seismic profiles (total length 3.5 km) acquired in 2013, combined with side-scan and single channel reflection seismic data along a river, which was believed to be important in the context of quick-clay landslides. Wireless (50-1C-10 Hz and 24-3C-broadband) and cabled sensors (323-28 Hz), 4-10 m apart, were used for the data acquisition of the longest profile (nearly 2 km long). Dynamite, accelerated weight-drop and sledgehammer were used as seismic sources. Simultaneous data acquisition for two parallel profiles, about 300 m apart, provides additional information. Preliminary results delineate the bedrock and its undulation near and in the river. We believe that overlying reflections are caused by the coarse-grained materials, whose lateral extension is considerably larger than previously thought. This may imply a wider area containing quick clay and hence at risk of slope failure. The new data and previous results are combined to construct a high-resolution 3D subsurface model that focuses on the coarse-grained layer and potential quick-clay areas. 

Malehmir A, Bastani M, Krawzyck C, Gurk M, Ismail N, Polom U, Persson L (2013) Geophysical assessment and geotechnical investigation of quick-clay landslides—a Swedish case study. Near Surface Geophysics, 11, 341–350