Experimental Study of Physical and Mechanical Properties of a Cemented Mine Tailings

The mechanical properties and behavior of mine backfill need to be better understood in order to increase the reliability of engineered backfill designs in deep and high stress mining conditions. The thesis makes a detailed examination of Cemented Paste Backfill (CPB) from the Williams mine with a range of cement contents, curing times, and confining stresses relevant to underground mining. The first major contribution is understanding how cement hydration alters the density of the backfill’s solid components. This understanding facilitates precise and accurate determination of cured backfill’s bulk properties, which is critical to accurate interpretations in the context of the next two contributions. The second major contribution is evaluating CPB response to isotropic compression at hydrostatic pressures up to 6.5 MPa, which is particularly relevant when considering how the backfill provides regional ground support during mine-wide ground closure with ongoing ore extraction. Equations of state are developed to quantify the initial elastic response, the onset of bond crushing, and the transition to a compacted state under large confining stress. The final major contribution is understanding CPB shear strength under drained triaxial loading, which is relevant to geomechanical backfill design for mining under, beside or through previously placed backfill. Backfill response is characterized by initially contractive behavior up to a Characteristic State of volumetric strain reversal, leading to peak dilation rate at the Failure State. Equations of state are developed to quantify this behavior. The combined state equations for isotropic and triaxial loading can form the basis for future constitutive models of backfill behavior. Such constitutive models, when incorporated into numerical analysis codes, will provide more confident back-analyses of observed backfill performance, and more realistic assessments of backfill behavior under different proposed mining scenarios. Each of these contributions is novel to CPB research, but also complements the broader body of literature on naturally and artificially cemented soils. Equally important, the thesis provides a framework to examine the mechanical properties and behavior of backfills from other mining operations.Ph.D