Optimization of the as-placed properties of hydraulic backfill

The use of hydraulically placed backfill in the deep gold mines of South Africa has increased rapidly over the past decade. The backfill that is delivered to the placement areas has a relatively high moisture content, and it is therefore pumped into geotextile containment bags that allow excess water to drain out but retain solid particles. The specjfic problems associated with this process that are addressed in this paper include the loss of solid particles entrained in the excess water, the rate of strength gain of the backfill, and the post-placement shrinkage qf the backfill. The results of laboratory, surface stope, and underground tests are descriptionbed. The parameters that were varied included the slurry density, the particle-size distribution, and the feed rate of the slurry; the concentration of added flocculant; and the type of geotextile used as containment. Suggestions are given for the optimization of the placement properties of backfill.