Unstable road cut slopes and design of retaining structures in the Rwandan context

The construction of new roads and the extension of existing ones on natural slopes often requires the excavation of very steep cut slopes. Such slopes become vulnerable under the influence of factors such as heavy rainfall, dynamic loading, weathering effect and various kinds of human intervention. Along several Rwandan main roads, cut slope failures recently caused a lot of damage to housing, infrastructures and crops as well as loss of lives. Based on field observations and variations in geological and geotechnical conditions, this paper presents a simplified way in which the classical geotechnical methodology could be applied to slope stability analysis, to be used for stabilization works. Three representative sample sites in the Rwandan context, recently subjected to landslides, were chosen to carry out a detailed study, including laboratory tests and numerical analyses. The conventional two-dimensional limit equilibrium method was used to analyse the representative cut slopes. Slope stability analyses are conducted not only to reproduce the failure events, to be used as back analyses, but also to propose potential remedial works, that could be assumed as an example for other similar situations. The obtained results show how, at least in most common situations, it is possible to obtain a reliable design for stabilizing works on cut slopes by applying classical geotechnical methodologies.