Assessment of Hazard and Contributing Factors of Landslides in Abay Gorge in Ethiopia

The role of engineering geology in the final design and construction of a road crossing the Blue Nile (Abay) gorge in Ethiopia is described. This new road between Mekhane Selam and Gundewein is a strategic link in the Ethiopian road network and encounters very steep and difficult terrain that poses significant engineering geological challenges. Remote sensing, landscape modelling, reference condition classification, and conventional field mapping have been applied to assist in the finalisation of the alignment, the prediction of ground conditions for earthworks design, and the implementation of slope and drainage protection works. The approach adopted serves as a blueprint for other road construction and improvement projects in the region though limitations exist with respect to the prediction of variable volcanic rock sequences at depth without the benefit of ground investigation boreholes. Although ground conditions different from those predicted have been exposed along 15 % of the alignment, these have been of relatively minor significance and have necessitated unanticipated remedial action affecting less than 2 % of the alignment in the gorge. Thus far, the main damage to the road from geohazards has been caused by roadrelated effects, including the concentration of road drainage below culverts and seepages from broken and blocked side drains. The susceptibility of the terrain to uncontrolled runoff is such that preventative and reactive maintenance will be required throughout the lifetime of the road.

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Slope hazards on the Ethiopian road network

Hearn¹

2018

QJEGH

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Jointed rock masses, adverse lithological sequences, often deeply-weathered soil profiles, seasonal rainfall, stream erosion and seismicity have created conditions favourable to the development of landslides in many parts of Ethiopia. Large, deep-seated landslides occupy many hillsides and some may date from the late Pleistocene–mid Holocene. Others are more recent and their activity is controlled by rainfall and, in some cases, the effects of land use change and road construction and widening schemes. The road network of Ethiopia has been expanding significantly over recent decades and has been impacted in many areas by reactivated ground movements and new, first-time failures. The Ethiopian Roads Authority (ERA) has undertaken a number of initiatives to combat these problems, including a research programme aimed at developing mitigation designs for 118 locations on the federal road network of the country. Engineering geological mapping formed the cornerstone of the geotechnical investigations, together with targeted trial pitting, drilling and geophysical investigations, that allowed remedial options to be scheduled. Nevertheless, geotechnical uncertainty prevailed at several locations, especially where ground investigation was precluded by budget constraints. A pragmatic approach had to be applied to the construction contract documentation that made provision for confirmatory ground investigation prior to design finalization and geotechnical inspection and interpretation during construction.

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Assessment of Hazard and Contributing Factors of Landslides in Abay Gorge in Ethiopia

Cited by 4 publications

References 1 publication

Case Example of GIS Utilization on Abay Gorge’s Landslide Survey in Ethiopia

Case Example of GIS Utilization on Abay Gorge’s Landslide Survey in Ethiopia

The role of engineering geology in the route selection, design and construction of a road across the Blue Nile gorge, Ethiopia

Slope hazards on the Ethiopian road network

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