Stress-strain behaviour of unsaturated compacted coal rejects and tailings

The paper presents the results of an experimental study aimed at evaluating the stress-strain response of unsaturated tailings (Mixed Plant Reject and Dewatered Tailings) from a mine in Queensland, Australia, which can be applied to further optimise current tailings disposal strategies of the mine. Triaxialtests at constant gravimetric water content were performed on specimens prepared at different compaction states using dynamic and static methods, to determine their shear strength. The dynamically compacted specimens display a higher strength than that statically compacted ones, which highlights the significance of stress history for tailings strength. As-compacted and post-testing suction measurements, performed using a high-capacity tensiometer, showed a reduction in matric suction irrespective of the material type, which is caused by mechanical wetting. The strength envelope was found to be non-linear, partly because of suction changes during testing. Post-testing suction measurement showed spatial variability within each specimen, with the central part of the samples experiencing the maximum suction reduction. The paper concludes with a discussion on the interpretation of such results.