Influence of tailings dam settlement on decant towers and pipelines

The Tailings Dam 4 Complex at Impala Platinum Limited is a large perimeter ring dyke impoundment with a potential storage of 770 million m 3 . The dam has a present surface area of 485 ha at 58 metres high and is designed to top out at 120 metres. This paper describes the results of tailings dam and decant structure settlement investigations, which have been carried out at the dam over a period of the twelve years. The settlement investigations form a part of an ongoing dam stability monitoring programme. This paper tables interim findings of specific settlement studies undertaken to predict long term movements associated with the two 5.5 metre diameter concrete decant towers and the twin 1350mm diameter nominal bore precast concrete pipelines under the dam. The precise survey and instrumentation monitoring systems are also discussed and the accuracy of the results analysed.