ABSTRACT
The objective of this study was to evaluate the causes and mechanisms of road damage in rift valley escarpments, using the case of Agoro-Shahigubi Road (northern Ethiopia), for the benefit of future road construction. The research involved: (1) inventory of geohazards and associated road damage, (2) investigation of the geotechnical properties of the slope materials involved, and (3) evaluation of impacts and geohazard management options. The inventoried geohazards included: rockfalls and debris/earth slides in 15 locations; slumps (small rotational failures) in 168 sites; blockages of 64 culverts (94 percent of the total number); siltation of roadside ditches (14.8 km; 45 percent of total ditch length); and scouring of roadside ditches (13.8 km; 42 percent of total ditch length). These interrelated and cascading hazards not only caused damage to the asphalt pavement, retaining structures, and hydraulic systems of the road, but they also affected traffic movements and incurred additional costs for maintenance. The main causes of road damage were: erodible soil and weathered rock, steep road excavations, unstable slopes, unmanaged concentrated surface runoff, hydraulic design limitations, and the placement of excavated materials onto sensitive slopes. The recommended solutions include: modification of road-cut slopes; removal of potentially unstable blocks from rock cuttings; improvement to road drainage systems; and integrated bio-engineering and water management solutions. The evidence from northern Ethiopia shows how various geohazards are interrelated and have cascading effects, requiring integrated geological, geotechnical, hydrological, and bio-engineering solutions to ensure sustainability and functionality of roads in this type of terrain.
