Subsurface characterization of a quick-clay vulnerable area using near-surface geophysics and hydrological modelling

Abstract

Abstract. Quick-clay landslides are common geohazards in Nordic countries and Canada. The presence of potential quick clays is confirmed using geotechnical investigations, but near-surface geophysical methods, such as seismic and resistivity surveys, can also help identify coarse-grained materials associated with the development of quick clays. We present the results of reflection seismic investigations on land and in part of the Göta River in Sweden, along which many quick-clay landslide scars exist. This is the first time that such a large-scale reflection seismic investigation has been carried out to study the subsurface structures associated with quick-clay landslides. The results also show a reasonable correlation with radio magnetotelluric and travel-time tomography models of the subsurface. Other ground geophysical data, such as high magnetic values, suggest a positive correlation with an increased thickness of the coarse-grained layer and shallower depths to the top of the bedrock and the top of the coarse-grained layer. The morphology of the river bottom and riverbanks, e.g. subaquatic landslide deposits, is shown by side-scan sonar and bathymetric data. Undulating bedrock, covered by subhorizontal sedimentary glacial and postglacial deposits, is clearly revealed. An extensive coarse-grained layer (P-wave velocity mostly between 1500 and 2500 m s−1 and resistivity from approximately 80 to 100 Ωm) exists within the sediments and is interpreted and modelled in a regional context. Several fracture zones are identified within the bedrock. Hydrological modelling of the coarse-grained layer confirms its potential for transporting fresh water infiltrated in fractures and nearby outcrops located in the central part of the study area. The modelled groundwater flow in this layer promotes the leaching of marine salts from the overlying clays by seasonal inflow–outflow cycles and/or diffusion, which contributes to the formation of potential quick clays.

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

“…Therefore, some aspects of the data acquisition, such as the geophone natural frequency, receiver spacing, seismic source, and receiver spread, restricted the frequency content of the surface-wave data, the signal penetration depth and resolution. Malehmir et al (2013a, b) and Salas-Romero et al (2019) described the reflection seismic data acquisition and processing for the seven seismic lines collected in 2011 and 2013 (this information is summarized in table S1 included in the supplementary material). The most important information about these surveys are that (i) the natural frequency of the cabled geophones was 28 Hz, except in the northern part of line 5-5b where wireless stations were deployed, alternating single-component (1C) vertical geophones of 10 Hz and three-component (3C) broadband digital MEMs (micro-electro mechanical systems) sensors, (ii) receiver spacing for the cabled geophones was 2-4 m and wireless stations were separated by 10 m distance, (iii) dynamite, accelerated weight drop and sledgehammer were used as seismic sources, and (iv) maximum receiver-source offsets are large, reaching up to approximately 2300 m in line 5-5b.…”

“…MASW studies do not require specifically designed data acquisition geometries or techniques (Neducza 2007;Konstantaki et al 2013;Pasquet et al 2015;Socco et al 2009), although the investigation depth can be increased by using long spreads and low-frequency geophones (Pasquet et al 2015). This study is based on applying MASW to a non-optimised dataset acquired for active-source reflection seismic processing (Malehmir et al 2013a;Malehmir, Saleem, and Bastani 2013b;Salas-Romero et al 2019) in an area prone to quick-clay landslides in southwest Sweden. Geotechnical characterisation of the site is then achieved by complementing the results from MASW with previous results from reflection seismic (Malehmir et al 2013a, b;Salas-Romero et al 2019), full-waveform tomography (Adamczyk, Malinowski and Malehmir 2014), Pwave refraction tomography (Wang et al 2016), radio-magnetotelluric (RMT) resistivity (Lindgren 2014;Shan et al 2014;Wang et al 2016) and borehole data (Salas-Romero et al 2016).…”

“…This study is based on applying MASW to a non-optimised dataset acquired for active-source reflection seismic processing (Malehmir et al 2013a;Malehmir, Saleem, and Bastani 2013b;Salas-Romero et al 2019) in an area prone to quick-clay landslides in southwest Sweden. Geotechnical characterisation of the site is then achieved by complementing the results from MASW with previous results from reflection seismic (Malehmir et al 2013a, b;Salas-Romero et al 2019), full-waveform tomography (Adamczyk, Malinowski and Malehmir 2014), Pwave refraction tomography (Wang et al 2016), radio-magnetotelluric (RMT) resistivity (Lindgren 2014;Shan et al 2014;Wang et al 2016) and borehole data (Salas-Romero et al 2016). The main objectives of this study are (i) to obtain 2D VS models, (ii) to estimate VP/VS and Poisson's ratio along the seismic sections with previously obtained VP models, (iii) to compare the new models with the geological data obtained in three boreholes drilled in the study area in order to make an integrated interpretation of the study site for identifying softer subsurface areas, and finally (iv) to find relationships between the models that could provide the quick-clay distribution in the area.…”

“…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.…”

“…The aim of this project was to study quick-clay landslides using different geophysical methods and to interpret and characterise the subsurface down to bedrock using an integrated analysis of several types of datasets. The studies using reflection seismic (Malehmir et al 2013a, b;Salas-Romero et al 2019), electrical resistivity tomography, cone penetration test with resistivity, and geochemical sampling (Löfroth et al 2011), core sampling and downhole property measurements (Salas-Romero et al 2016), and Pwave refraction tomography and RMT resistivity (Wang et al 2016) revealed the subsurface structures and provided information on a coarse-grained layer underlying potential quick clays in some locations.…”