Robertson GeoConsultants was appointed by Wismut to develop the methods and technology for the placement of cover layers on the very soft (weak) tailings in the pond zone of the Helmsdorf tailings impoundment. These extremely weak (essentially fluid) tailings require special techniques to increase their consolidation sufficiently to enable conventional cover placement techniques to be used. This study involved the use of finite strain consolidation theory to develop a model which predicts the rates of consolidation and pore pressure dissipation within the slimes zone under self weight as well as the incumbent loads of cover layers and placing equipment. The effects of short and long band drains were modelled for both short and long term effects. Available computer codes were not able to perform the modelling, and additional model development had to be done for the project. The study resulted in the development of alternative cover placement methodologies and the demonstration of the analytical methods for their design.

RGC also participated in the performance (with Wismut and other Wismut consultants) in the development of risk analyses for alternative tailings remediation methods to enable the alternative which provided the best long term cost benefits to be identified and to provide a rational for alternative selection.