Three dams (Bridle Drive, Lesapi, and Xonxa) were constructed in southern Africa between 1970 and 1975 making use of downstream zones of reinforced rockfill to control major construction floods. In the cases of the Bridle Drift and Lesapi dams relatively minor failures occurred when floods passed over the partly constructed embankments, while at Xonxa a major failure occurred.
From these failuers and from the successful performance of the Googong dam, completed in 1978 near Canberra, conclusions are drawn regarding the important factors to be considered in the design and construction of reinforced rockfill dams of this type.
By Philip J N Pells
Because of the expected high cost of embankment raising under the current tailings disposal strategy at a mine in NSW, Australia, FLAC analyses have been undertaken to study the strength gain due to consolidation in the Stage 1 dam. The problem is summed up as a two-dimensional consolidation procedure with incremental construction of the consolidating medium. The numerical modelling allowed porosity and permeability to be a function of accumulated volumetric strain, the drained modulus to be a function of depth of tailings and the undrained shear strength to be a function of the vertical effective stress. These procedures are implemented by means of a FISH function. Different modelling approaches have been carried out and compared. The results from the analyses indicate that the high rate of filling of the reservoir will preclude sufficient strength gain of the tailings to allow upstream construction as presently planned.
By C Dai & Philip J N Pells
By S E Pells and R Fell