Stability and Settlement Characteristics of Hydraulically Placed Mine Tailings & Power Station Fly Ash

Fine silt-sized waste particles are often disposed of by being mixed with water, pumped to a void and allowed to sediment. The resulting ‘soil’ has a very loose structure which makes it difficult to test. There is interest in these materials, e.g. for site redevelopment. This paper describes the preparation of very loose samples of pulverised fuel ash and mine tailings from fluorspar production, in an attempt to replicate the structure of hydraulically deposited fills. The results of oedometer and triaxial tests are also presented. Difficulties in sample preparation and measuring e_max are described. The use of Bolton’s (1986) relative dilatancy index to describe the drained behaviour of such deposits is discussed. The materials display varying degrees of instability in undrained loading that may be dependent on stress level, particle shape and size distribution.