UNDERWATER CONSTRUCTION OF AN EMBANKMENT TO EXTEND THE LIFE OF A TAILINGS IMPOUNDMENT

The dam of a valley tailings impoundment at a South African diamond mi ne was originally constructed of loosely deposited coarse tailings. Th e fine tailings were then deposited hydraulically behind the dam. The dam was raised to its present height of 60 m in the 1950s. After initi al problems with shear stability that were remedied by constructing to e drains and buttresses, the dam has continued in use up to the presen t day. With the impoundment almost full, and the hydraulically deposit ed tailings covering an area of 350 ha by 1990, the dam required to be raised if the impoundment was to continue in operation. One of the pr oblems of raising the dam was that tailings and water had pushed up a side valley, and would encroach on the golf course and mine village if the tailings level rose appreciably higher. This Paper relates how an embankment was constructed underwater to protect the mine village, an d also the methods chosen to raise the dam. Model tests in the laborat ory showed that underwater construction was quite feasible, and the un derwater embankment was successfully constructed in a very short time. Tests associated with the raising of the dam, and the system adopted for its construction are also described.