Regional rockfall exposure assessment, experiences from Serbia

Abstract

Rockfalls are common in hilly and mountainous areas, especially along roads with engineered slopes and cuts. Such is the case for most of the state and local road routes in Central, Serbia, which was the subject in this case study. A road network of 276 km covering roughly 1700 km2 bewteen the cities of Kraljevo, Čačak and Ivanjica is presented. Assessing of such wide areas needs to be conducted from large to site-specific scale, i.e., using GIS spatial tools and 2D-3D stability models, respectively. The regional scale of assessment using GIS tools was in focus. The primary input was the Digital Terrain Model, obtained from open data ALOS mission at 12.5 m resolution, as well as appropriate sheets of geological maps at 100k scale. The first step was to delineate areas that can host unstable blocks by inspecting planar sliding kinematic condition against available data. These included raster data (slope angle and azimuth) but also, point-based data (discontinuities’ strike, dip and friction angle) which had to be estimated or interpolated across the area by various GIS operations. In total, there were nearly 5000 potential detachments delineated. Further step was to run the rockfall simulation by using these detachment zones as initiation sources in a simple kinetic model CONEFALL, standalone software. The output model simulated several thousands of rockfalls, with various runout distance (<650 m), velocity (<46.5 m/s) and energy (<540 kJ). When overlapped with the road network, this model revealed the road exposure to rockfall. Locations with runouts that reached the road lines make about 6.7 % of the total network length. Zones of estimated energies higher than serviceable threshold (300 kJ) occupy 0.9 % of the total and require additional remediation design. Presented analysis is a promising tool for supporting planning and decision making in the road management sector.