Integrated Interpretation of Electrical Conductivity Changes, Heat Generation, and Strength Development in the First Week in Cemented Paste Backfill

Estimating the as-placed properties of mine backfill is fundamental to optimizing the safety and productivity of underground mines. For Cemented Paste Backfill (CPB) an important consideration is the extent to which self-weight consolidation during deposition may reduce the void ratio and enhance the binder’s effectiveness. Field monitoring and sampling campaigns can help investigate this phenomenon but they are expensive and logistically difficult. Therefore, mesoscale column experiments are performed in the controlled laboratory environment to better understand the coupling between self-weight consolidation and cement hydration. In this paper, columns are backfilled with uncemented paste tailings and with CPB and the pore water pressure, electrical conductivity, and volume changes are monitored during and after backfilling. The pore water pressure profiles at the end of backfilling are compared with an available analytical solution and restrictions on the solution’s validity are identified. Void ratios of samples taken from columns are compared with the ones obtained from field samples and the similarity indicates the filling conditions simulated in the laboratory are representative of field conditions. The changes in void ratio after curing were small compared to the initial void ratio of fresh CPB. The tests’ results help explain why self-weight consolidation during backfilling is not significant at the studied mine, which may be the case for many other mining operations as well.

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Evaluating Cemented Paste Backfill’s Strength Development at Early Age Using the Laboratory Vane Shear Test

Yue

Jafari

Grabinsky

2023

Geotechnical Testing Journal

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The Unconfined Compressive Strength (UCS) test is the most widely used method in the underground mining industry to assess strength development during binder hydration. However, testing errors are common for weak materials (UCS less than 100 kPa, i.e., cemented paste backfill at early curing stage), and reliable test methods must be established for designs relying on early age strengths, particularly for continuous pours. Therefore, the standard geotechnical laboratory vane shear test is investigated as an alternative. A newly designed “cast-in-place” mold is used to avoid specimen damage arising from vane insertion. Parametric tests with vane rotation speeds of 30 to 120 degrees per minute show strength insensitivity to these shear rates. Vane shear strengths correlate linearly with UCS over the strength ranges used; however, the trend does not follow the usual assumption for clays in the undrained state, because the material does not shear at a constant volume as clays do. The influence of suppressed dilation is investigated using direct shear tests, but these results do not fully explain the discrepancy, suggesting other mechanisms also have an important influence. Therefore, vane shear tests can provide a useful complement to UCS tests not only at the laboratory scale but in the in situ condition for early strength characterization. It should be noted that the correlation to UCS must be considered empirical, and separate calibrations are required for each backfill material.

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Integrated Interpretation of Electrical Conductivity Changes, Heat Generation, and Strength Development in the First Week in Cemented Paste Backfill

Cited by 3 publications

References 52 publications

Evaluation of active silica-alumina content and reactivity in bayer process red mud

Evaluation of active silica-alumina content and reactivity in bayer process red mud

Simulation of cemented paste backfill (CPB) deposition through column experiments: comparisons of field measurements, laboratory measurements, and analytical solutions

Evaluating Cemented Paste Backfill’s Strength Development at Early Age Using the Laboratory Vane Shear Test

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