Geomechanical analysis through distinct element modelling of the rockslide Gámanjunni 3, Troms, Norway

The rockslide Gámanjunni 3, with an estimated sliding volume of 26 Mio. m³ and an annual movement up to 5 cm, is classified as a high-risk object. Hence, the site is subject to continuous monitoring, including global navigation satellite system receivers (GNSS), a ground-based radar (GB InSAR) and a meteorological station. Several studies have analysed the patterns of movement and developed different interpretations of the internal structure of the shear zone and sliding body. The presence of permafrost in the sliding body was investigated in earlier research. Its degradation, togehter with variation in joint water pressure is assumed to be a significant trigger for the rock slope displacement, beginning in mid-Holocene.

Our work aims to investigate the influence of rock mass parameters, geometry of internal structures, ongoing displacement and climate driven triggers on the stability of the slide. This is done by using a model of the universal distinct element code (UDEC).

Prior to the numerical modelling, we analysed the current movement data, visible structures in the backscarp and the results of previous studies. Due to partly contradictory results, several versions for the geometry of the basal shear zone were developed. Based on own field work and earlier investigations, representative sets of rock mass and joint network parameters were estimated.

In the first modelling stage, scenarios with increasing degree of complexity were used to test the sensitivity of the results on the input parameters and the numerical setup. The parameters  were calibrated in order to fit the model output with the observed displacement. In the subsequent stage, the stabilisation trend under progressing displacement is investigated for the different versions of shear zone geometry. Additional model scenarios include climate driven triggers, such as groundwater and permafrost.

The results of this case study should improve the understanding of the behavior of rock slope displacements in response to inherent parameters and triggering factors. Further research will focus on the effects of various climate change prediction scenarios on the stability of the slope.