Some slope stability problems in soils derived from the Ecca Shales of Natal,South Africa

Shales of the Lower Ecca stage of the Late Palaeozoic Series are actively degrading in the particular topography and climate of Natal. The failure of a large road embankment near Pietermaritzburg and the subsequent failure of the adjacent natural slope were caused by movement along existing shear zones in the underlying colluvium. Other cases of instability in both natural slopes and engineering earthworks are known, in the Pietermaritzburg and Durban areas and elsewhere in Natal. These failures in various types of slope in different parts of Natal suggest an inherent instability in colluvial and residual soil derived from shale of the Lower Ecca stage.