A comparative analysis of the results of terrestrial laser scanning and numerical modelling for assessing the stability of a road embankment on the active landslide on the Just mountain at Tęgoborze at Just – Tęgoborze

This article presents a method for the quick assessment of the safety of the road on an active landslide on the Just mountain at Tęgoborze using the landslide hazard ratio of landslide movements. The hazard indicator for landslide traffic has been defined as the quotient of the largest displacements obtained from measurements using a terrestrial laser scanner to the largest displacement obtained from a numerical model of the worst geotechnical conditions and an unstable landslide. The application of this indicator was presented on the example of national road No. 75 along the section of the road in km from 51 + 900 to 52 + 700 at the location of the Just mountain at Tęgoborze in the south of Poland. The road is located on an active landslide and has a lot of traffic. The measurements were conducted with the RIEGL. VZ400 terrestrial laser scanner from 2012 to 2016. As a result of the measurements performed with a terrestrial laser scanner, a cloud of 3D points was obtained. Differential models of subsequent measurements were constructed and compared to the first base measurements. The results of 3D differential models obtained from terrestrial laser scanner measurements were compared with results obtained from 3D numerical modelling. Numerical calculations were conducted assuming the worst geotechnical conditions. The model of the landslide was fully saturated. A numerical simulation computed using the finite element method (FEM) in the MIDAS GTS program was applied. A result of the safety factor F = 0.8 (i.e. an unstable landslide) was obtained. In order to estimate the hazard, the values of the landslide hazard indicator were determined for each date using the measurements conducted with the laser scanner.