Determination of Terrain-Specific Restitution Coefficients and Rockfall Hazard Assessment in the Chaku Bazar of Nepal

Many of Nepal's rapidly growing cities are located at the base of steep slopes, where rockfall hazards pose a significant threat. Rockfall issues have also been observed in Chaku Bazar, Sindhupalchowk, Bagmati Nepal, situated at km 102+000 along the Araniko Highway. The primary aims of this study were to determine the restitution coefficient of the material, stability analysis and to simulate rockfall at the steep slope in Chaku Bazar. The accuracy of rockfall simulations relies on the restitution coefficient. Initially, the normal and tangential restitution coefficients were calculated for 10 different rock boulders, varying in shape and composition using the Tracker Video analysis and modeling tool. The computed values for normal and tangential restitution coefficients were then used to simulate rockfall behavior using GeoRock 2D across four different sections, predicting rockfall trajectories and run-out distances. Geologically, the area is part of the Lakharpata Group of the Lesser Himalaya, characterized by calcareous rocks, primarily dolomite and schist. The normal restitution coefficient for vegetated rocky terrain was 0.25, while for solid rock it was 0.73. Likewise, the tangential restitution coefficient was 0.37 for grass-covered areas and 0.82 for rocky surfaces. The factor of safety of block for planar failure is 0.83, for wedge failure is 0.95 and for toppling failure is 1.35. After determining the restitution coefficients, the calculations revealed a maximum collision energy of 2576 kJ and a maximum bounce height of 4.6 meters.