ABSTRACT
Open excavation refers to the removal of material, within certain specified limits, for mineral exploitation and construction purposes. For this to be accomplished economically and without hazard, the character of the rock and soil masses involved and their geological setting must be investigated. Indeed, the method of excavation and the rate of progress are very much influenced by the geology of the site (Kummerle and Benvie, 1988). Obviously, the stability of a rock or soil mass is important in excavation, as are the position of the water table in relation to the base level of the excavation, and any possible effects of excavation on the surrounding ground and structures. Open joints in rock masses facilitate weathering and generally aid slope failure. Fissure zones usually represent zones of weakness along which rock masses may have been altered to appreciable depth by weathering. Faults that traverse the area in which excavation is to be made may cause serious trouble. This is principally because of the greater freedom afforded rock masses to move along fault planes. In particular, if a fault intersects a prominent joint or bedding plane in such a way that it produces a wedge that daylights into the excavation, then this is likely to slide. The cross-section of an open excavation is influenced by the dimensions of the base, its depth
and the profile of its slopes. In terms of construction, in particular, slopes should be as steep as possible, consistent with safety, in order to minimize the volume of material to be removed. Allowance must be made for any drainage works as far as the dimensions of excavations are concerned.
