Slope Stability of Benguela and Lobito Urban Areas, Western Angola, Using RHRS

Abstract

A study of slope stability in the Benguela and Lobito areas, in Western Angola, was carried out. Seven slopes are studied. Three of the slopes are located at the urban area of Lobito, the other three are situated at Catumbela and one is located in the Caota’s area. The majority of the slopes are essentially composed of intercalations of limestone and marls belonging to the Quissonde Formation of the Cretaceous period. The methodology adopted in this work was useful to identify and characterize the different stability problems of the slopes. The Rockfall Hazard Rating System (RHRS), established by Pierson et al. (1990), was used to define the potential hazard for the roadways users. RHRS permits an analysis of the rockfall on roadways with relative low costs and can be applied in undeveloped countries, where the measurements devices are limited or scarce. Different types of slopes failures have occurred such as rockfalls, flows and landslides. The main causes of the slope movements are rainfall, slope geometric modification, rapid urbanization and roadway construction without the necessary geological and geotechnical characterization. The areas, of the studied slopes belong to dry tropical climate of arid and semi-arid characteristics, nevertheless torrential rainfall episodes can occur and initiate hazardous landslides. The majority of results of RHRS for the different slopes lie between 300 and 500. The results analysis allowed the adoption of mitigation and prevention measures.