Abstract
Mountain roads play a vital role in the development of southwestern Saudi Arabia, as they were built in a difficult terrain. This part of the country is characterized by high-rising and steep slope mountains. This forms a natural obstacle to man-made road alignment 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 12 km portion of such mountain road, in this study, that 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 rockfalls. The man-made rock slope cuts are 70 degrees-90 degrees, and reach up to 40 m height. Many of these slopes are dangerous and potentially unsafe due to rockfalls. The source of rock blocks is from upper slope elevations. Absence of ditches and meshes aggravate the conditions under the slopes. In this research, the rock masses were studied in order to identify the decisive parameters of rockfalls, and applied the Rockfall Hazard Rating System on such steep man-made and natural rock slopes. Parameters such as slope angle, restitution coefficient, rolling friction coefficient, bounce coefficient, trajectories, effect of block size and geometry were studied. Colorado Rockfall Simulation Program (CRSP) modeled the most important rolling factors on rockfalls. According to this study, remedial measures were suggested according to the site conditions and the dominant parameters utilizing the latest technology to arresting fallen blocks.