A Comparison of Different Laboratory Techniques to Simulate Stress and Moisture History of Hard Rock Mine Tailings

Abstract

In thickened tailings technology, tailings are depo sited at solids concentrations sufficient to preven t segregation and allow for formation of gently sloped stacks. Po st-deposition, thickened tailings are known to gain strength through a combination of hindered settling, desicca tion, and consolidation. Recently, it is understood that the shear strength and geotechnical stability of the st ack is dependent on the degree of desiccation or dr ying time for a given layer, as well as consolidation history dur ing subsequent deposition. This paper presents some preliminary investigations into how best to reprodu ce this stress history for element testing. Three l aboratory methods for simulating stress history of thickened tailings layers are introduced for preparing sample s for testing in an NGI type simple shear apparatus. In the first method, tailings are reconstituted in the simple s hear mold, desiccated to different degrees, and re-wetted befo re shearing. The second method consists of simulati ng the thickened tailings deposition in a column, followed by sample extraction using a shearing thin-wall sa mpler. In the third method, a flume is employed to simulate t he movement of thickened tailings layers from the d eposition point down the beach. The third method is intended to assess whether the movement of tailings down the beach constitutes an important part of stress history, an d influences the evolution of the fabric. This pape r recommends the most appropriate method for preparing samples t o assess the geotechnical behaviour of thickened ta ilings. It is concluded that desiccation to the shrinkage limi t could significantly increase the monotonic shear strength of hard rock mine tailings; however, with continuing d esiccation beyond the shrinkage limit, additional monotonic strength gain is minimal.