4.1 Dump Configuration
The configuration and the size of a mine dump have a direct impact on its stability and potential size of failures. The primary geometric variables are:
Height of the dump: It is defined as the vertical distance from the dump crest to the ground surface at the dump toe. Dump height typically ranges from 20m to more than 400m. It is an important characteristic for stability, mode and speed of failure, and potential runout distance. In general, dump height is predetermined by the mine site physiography and mining rate. The ultimate toe of a dump is dictated by the volume of material to be placed depending on the size of the area or the depth of the valley.
Volume: Small dumps are considered to contain less than about 1 million m3, while large dumps have more than 50 million m3. Medium sized dumps have volumes in the range of 1 to 50 million m3.
Slope Angle: The overall dump angle is measured from crest of the uppermost platform to the toe. The normal range of dump slopes is between 26° to 37°, the lower value commonly adopted for reclamation whereas the upper value corresponds to the free dumped cohesionless rockfill. Slopes steeper than 37° may also occur if the dump material contains appreciable fines or cohesive material, or consists of very large, angular boulders.
Foundation Slope and Degree of Confinement
The foundation slope and degree of confinement afforded by shape of the foundation also affects dump stability. The most favourable situations are a decreasing slope towards the toe (i.e. a concave slope), and three-dimensional confinement within a valley.