Shear strength estimation for Åknes sliding area in western Norway

This paper deals with the unstable rock-slope at Åknes sliding area, located in the county of Møre and Romsdal in western part of Norway. The sliding body has a complex geometry with several sliding planes at different levels, involving unfilled joints, gouge material/brecciated material as well as bridges of intact rock. Stability of the rock slope strongly depends on the shear strength of the sliding plane(s) and this paper discusses the shear strength of the materials present, ranging between the strength of intact rock and crushed, clay containing gouge material. Estimation of the in situ shear strength at the Åknes sliding area is discussed on the basis of triaxial test results and the Barton–Bandis empirical method. Triaxial tests have been carried out on samples of gouge material from a potential sliding plane and intact rock specimens, while the empirical method has been applied for rock joints in the area. Comparison and correlation with experimental results found in literature have also been made. The resultant shear strength range for the zone of sliding has been found to be in the range of 0.5–1.3 MPa, depending on the normal stress and the composition of the sliding zone.