@@Mountain roads are a challenge for engineering and for development of southwestern Saudi Arabia, as they were built in a difficult terrain. This part of the country is characterized by harsh high-rising mountains and steep natural rock slopes. This forms a natural obstacle to road construction operation and the engineered slope-cuts. Abha-Al-Darb mountain road of almost 50 km long lies at one of the harshest terrains in Saudi Arabia. A 2 km portion of such mountain road, in this study, lies along sharp cliff suffers from frequent rock falls, mainly in rainy seasons, in addition to various types of slope failures. The rock masses are mainly schist of high grade metamorphism. The foliation of the schistosity dipping towards the rock slope cuts, causing a frequent occurrence of mainly toppling rockfalls. The dip of the man-made rock slope cuts are 70°-90°, reach up to 40 m height in some places. Some of the rock slopes are not stepped. Accordingly, many of them are dangerous and potentially source areas of rockfalls from upper slope elevations. Absence of ditches and meshes aggravate the road conditions under such slopes. In this research, the relevant geotechnical properties of the rock masses were studied in order to identify the decisive parameters of rockfalls, also applied 1) the Rockfall computer program and 2) Rockfall Hazard rating System on such steep man-made and natural rock slopes at a problematic part. Parameters such as slope angle, restitution coefficients, rolling friction coefficient, bounce coefficient, trajectories, effect of block size and slope geometry were studied. According to this study, remedial measures were suggested according to the site conditions and the dominant geotechnical parameters utilizing the latest technology to prevent fallen blocks from reaching the road.
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