Geological parameters and shear strength of dry tills from the southern half of Norway in relation to bedrock geology

When excluding floods, it is primarily slope stability issues such as landslides and avalanches, which count for the main geohazards in Norway. Till is the dominant Quaternary sediment, where the till deposits mostly originate from local rocks with a transport distance less than five kilometres. Consequently, debris slides and debris flows are among the main geohazards on till-covered valley slopes. In this context, the shear strength of tills is poorly studied. In addition, available documentation and data supporting so-called ‘known relationships’ of bedrock geology to geological parameters of till, such as particle size distribution, particle shape, and the mineralogical composition seem to be rather poor or based on outdated or nonstandardised test methods. These geological parameters are also known to influence soil shear strength. To improve the knowledge on this subject, a set of 33 nearsurface, genetically independent till samples were collected from various locations in the southern half of Norway to investigate the relationships between shear strength, geological parameters, and bedrock geology. The samples were categorized into six regional rock provinces, i.e., the Precambrian basement, the Oslo region, and four provinces in the Caledonian orogen, with five to seven samples in each. The mapped rock type(s) assumed to represent the origin of the till samples were based on their area of extent around the sample sites, and adjusted for by the late Weichselian ice-flow directions. Furthermore, the disturbed samples were sieved (