AVSÄTTNINGSMILJÖ OCH STRATIGRAFINS ROLL I BILDANDET AV KVICKLERA En studie om skredkänslighet i Västra Götaland

Abstract

Landslides have historically been a major issue in Västra Götaland, Sweden. They have caused significant damage to infrastructure with events such as the landslides in Stenungssund 2023 and in Tuve 1977, with even lives being lost in such cases. In Västra Götaland the landslide susceptibility is mainly due to the presence of the sensitive quick clay found in the region. This study aimed to investigate the formation of quick clay by connecting the depository environment and the presence of more permeable sediments in conjunction with marine clay. This was conducted to simplify the identification and mapping of quick clay. To achieve this, an area was mapped in QGIS, considering the distance to permeable deposits, including geomorphological features such as moraine, eskers and historical shorelines, with their adhering sedimentary deposits. This mapping resulted in a classified area which was deemed as elevated risk of quick clay formation. The area was then used to delimit previously identified landslide scars, as mapped by the Swedish Geological Survey (SGU) and Swedens Geotechnical Institute (SGI). These delimited landslide scars were subsequentially mapped by area, length, and width. Then categorized and statistically analyzed to find landslides which had the probability of originating from quick clay based on morphometrics. This resulted in the identification of four previous landslides, which were further analyzed using pre-existing borehole data to examine the stratigraphy of the landslide masses. The main findings and conclusions include that all four investigated landslides had a connection to permeable deposits in their stratigraphy, with two of these having an alternating sequence of clay with more permeable sediments. Also, a majority of the landslides in the Västra Götaland region were within this classified area of heightened quick clay susceptibility. From this, the conclusion was drawn that there is a connection between quick clay formation and the presence of more permeable deposits. Furthermore, some interesting correlations could be found between previous landslides, primarily regarding shape and land slide energy. Furthermore, correlations between previous landslides were observed, particularly concerning shape and landslide energy, as well as latitude and landslide area. For further studies more in-situ analysis could be beneficial, such as geotechnical investigations to see how well the classified area performs at identifying areas with quick clay. While also possibly mapping landslides and landforms such as eskers and moraines to refine the classified area.