Design of Larger Span Overhanging Cliffs Constructed in Himalayas

Road construction and maintenance is challenging in Himalayan region of Pakistan. The operators must deal with slope stability issues and falling rocks. In addition, the slope heights are huge that have a greater impact on economics and feasibility of operations. To deal with this situation the contractors create a slot (or overhanging cliff) in the base of the slope, especially in competent rock. These address some of the issues like reduced excavation costs and avoiding tumbling rock falls from top of the slope. Thus, it reduces overall excavation cost and construction time. While the occasional fall of rocks and debris on the highways is diverted by hanging cliff or rock cover, the construction design of these structures is purely based on experience. The problem add-on when an expansion in span or height is desired in existing roads. This paper summarizes the stability study of overhanging cliffs and evaluates its design in challenging ground. An extension of a national highway case study for existing span of 7 m tunnel is studied. Numerical modeling is used to study the stability of road overhanging cliff. Different scenarios are modeled in consultation with the field practitioners and a stable design is proposed for extension.