Geotechnical assesment of landslide-prone road cut slope zone (study case: Jabungan-Mluweh street, Semarang, Indonesia)

Geotechnical is a branch of Geological science that studies soil and rock and their relation to the surrounding buildings. Geotechnical assessment on a slope that is indicated to be prone to landslides is very important to do, especially if the slope is in a location that is often passed by humans. In this paper, a geotechnical assessment is carried out on the landslide-prone road cut slope on the Jabungan-Mluweh Road, Semarang, Indonesia with the aim of knowing the level of vulnerability to landslides on the slopes around the road. The method used is remote sensing and field observations. The remote sensing methodology for determining the distribution of landslide-prone by 5 parameters, that is rock resistance, land use, slope, fault fracture density, and normalized difference vegetation index. After that, detailed observations were made in the field and it was found that there were 10 locations prone to landslides, at those 10 locations a more detailed analysis was carried out to determine the geological strength index (GSI), slope geometry, and joint conditions. Slope modeling is done using phase 2 software by finite element method. The results of the analysis show that Geotechnical assessment on road cut slopes can be done using laboratory data, but an empirical approach using Schmidt hammer rebound value (SHRV) can also be applied in the assessment if the observed terrain is quite difficult and dangerous. The slope stability analysis show that there are 7 slopes in unstable conditions, 1 slope is marginally stable, and 2 slopes are stable. Therefore, several suggestions are proposed to forstrengthen the stability of the cut slope.