Evaluation of Factors Influencing Slope Instability: Case Study of the R523 Road Between Thathe Vondo and Khalvha Area in South Africa

Abstract

The R523 road links Sibasa to Nzhelele area; it passes through Thathe Vondo and Khalavha. This road presents an important corridor in the area which connects different villages. Sustainable and affordable rural access is a necessary pre-condition for expanding socio-economic opportunities to the different villages. The road is also important to the operation of Thathe Vondo plantation and Tshivhase Tea Estate. Slope failures along busy roads do not only have the potential to cause fatalities and injuries but can also cause serious disruption to traffic. Slope failure of cut-slopes along a road presents a serious problem in most mountainous roads, causing damages to roads, buildings and other structures as well as disrupting the activities of the local people. They also threaten the lives of the people themselves. The road had been excavated using blasting and mechanical operation on the topographically challenging terrain of increasing slope height, inclination and altering slope shape forming an unstable slope, which, along with various other adverse geological conditions, causes slopes to fail during heavy rains, creating damage to property and blocking the road. The road construction has subjected the area to an intensive mass movement. The road construction changes the existing slope geometry and groundwater regime enough to unbalance driving and resisting forces on a slope that was in equilibrium, subjecting the area too unstable conditions. The road has been constructed with insufficient considerations of measures to prevent soil erosion and deposition of silt soil in the water channel. The construction of the road left many cut-slopes, which are difficult to rehabilitate to the original stability condition because the earth material was disturbed. The road also passes through areas of different geological hazards (debris flow, soil erosion and weathered zones). The different environmental factors, such as intensive summer rainfall and human activities, in the study area make the road susceptible to frequent slope failure from time to time.