Design considerations for hydraulic backfilling with coal combustion products (CCPs) at high solids concentrations

The rheological characteristics for the complex hydro-mixture of coal combustion products (CCPs) such as fly ash and fly ash-bottom ash mixture slurry at high solids concentration in the range of 60–70% by weight were investigated. Based on the rheological data, a non-Newtonian pseudo-plastic power law head loss model was used to evaluate the head loss of ash slurry pipelines having nominal bores in the range of 100–300 mm. The results indicated that the addition of bottom ash fractions to fly ash slurry at a given solids concentration has a beneficial effect in reducing the pumping power requirement. A monogram (design chart) for the ash mixture slurry has been formulated indicating the variation of backfilling rate WS with H/L ratio for a range of pipe sizes and transport velocities which may provide relevant pipe flow and operational conditions for hydraulic disposal of these coal combustion products for mine backfilling purpose.