Remediation and mitigation strategies for rock fall hazards along the highways of Fayfa Mountain, Jazan Region, Kingdom of Saudi Arabia

A rock fall hazard rating study was conducted along the roads of Fayfa Mountain in the Kingdom of Saudi Arabia to determine hazardous zones and to specify remediation and/or mitigation measures to improve the safety of the steep mountain roads. The mountain consists mainly of a weathered and/or fractured syenite core draped with slate, phylitic, and amphibolite rocks around the lower periphery of the mountain. Overall slopes on this mountain have an average range between 38 and 45 degrees, with rock cuts typically 30-40-m high in places. High-value properties dot these mountain roads, and when roads are closed because of rock fall, there is significant personal and economic disruption in the area. This study was concluded in 2011, and rock fall hazards were indentified and classified according to relative hazard (likelihood of rock fall) and relative consequence (consequence of rock fall). For this purpose, the Saudi Arabia Rock Fall Hazard Rating System was developed based on existing rating systems. In addition, remediation and mitigation measures were prescribed for each identified hazardous section. Specified solutions were geared to minimize cost and to make use of local expertise and available equipment. The suggested remediation solutions are scaling of loose rock (both manual and mechanical), mechanically reshaping the slope (to remove overhangs and remove protrusions that serve to increase the horizontal velocity of bouncing and rolling rock), increasing the ditch capacity by deepening and widening the ditch (often by cutting back the lower portion of the slope), or by installing jersey barriers on the down gradient side of the ditch, using locally built stone retaining walls to stabilize the lower section of slopes and using gabion and large block barriers to stabilize small debris flow channels. In a small number of cuts, trim blasting and creating benches were specified. Some solutions were not considered due to high cost or due to the concern that local contractors could not implement them effectively. These included anchoring systems, advanced walls such as sheet pile and anchored retaining walls, draped mesh, and sacrificial fences.