ROCKFALL HAZARDS ALONG ABURI-ACCRA ROAD, GHANA

Abstract

The expansion of the Peduase-Ayi Mensa road along a section of the Akwapim-Togo Range required excavation forming rock-cut slopes. These exposed the rocks face to geologic and climatic conditions influencing weathering. Even though ditches and benches have been constructed in some sections, rock falls still occur. The exposure of road users to rock fall hazards puts human lives and properties at risk. This study, therefore, sought to determine the factors influencing rock fall and evaluate slope face using the Modified Colorado Rock Fall Hazard Rating System (MCRHRS) for contribution to policy considerations on measures to prevent these failures. The study area was purposively divided into thirty-five sites. In determining the factors influencing the failure, observations were made to identify types of rocks and describe the nature of distinct joints. Interviews were also conducted to seek information on the causes and management of rock falls. Furthermore, observations and measurements of parameters were used to evaluate sites with MCRHRS. Total RHRS scores obtained from the evaluation of sites, in addition to aerial photographs, were used to map the degree of rock fall hazards at each site. Findings from the study indicated that rock fall hazards are influenced by the physical disturbance of the geology of the area during the construction of the road and buildings, unfavourable slope angles at some sites, in addition to rock mining and rainfall. Also, evaluation of sites indicated that RS11 is most likely to fail and hence requires higher priority of remedial works. In the course of the study, vegetation along the slope face and a section of the natural slope from RS35 to 18 were removed for the installation of wire mesh. Since it still occurs, the removal of weathered rocks and spraying of fibrecrete onto the slope face could also be considered.