Cemented paste backfill (CPB) has been an important contributing factor to enhanced economic and environmental sustainability of many bulk mining operations, primarily because of its rapid rate of delivery (as compared to other forms of backfilling) and the fact that tailings are recycled as backfill, thereby reducing the volumes of both solids and water that would otherwise be directed to a managed tailings facility. However, the physical properties of CPB are significantly different from other forms of backfill, notably hydraulic fill and cemented rock fill, and there remains significant opportunity to optimize the geomechanical design of paste backfill systems for underground mining. Particular attention must be paid to the paste's ability to retain water through matric suction, and this phenomenon is typically enhanced by the hydration of binder within cemented pastes. These suctions can significantly enhance the paste's strength and liquefaction resistance, which has important implications for the design of fill barricades, the use of fill plugs to protect barricades, the rate of fill over top of the plug, and the time to resumed production blasting in proximity to a recently filled stope. To obtain better information regarding the behaviour of CPB in situ, a new instrument cluster is proposed. The cluster uses multiple total stress cells with a tiltmeter to verify the ultimate orientations of these cells, piezometers for total pressure and heat dissipation sensors for matric suction, a thermistor for temperature measurement, an electromagnetic probe for determination of conductivity and dielectric permittivity (which give information about the stage of hydration and the bulk properties of the paste), and dynamic transducers for pore pressure measurement and for acceleration. All of the instruments are attached in a cage (see figure) and the paste can readily flow through this cage and around each of the transducers. The small size of the cluster (less than 1 m~3) allows information to be collected within a relatively homogeneous portion of the fill mass.
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