A model study for blind pneumatic backfilling of fly ash in abandoned underground mines

This paper describes a model study of the flow phenomena in a pneumatic backfilling technique that involves application of short-duration high-pressure impulses. The study involved using fluidized bed combustion (FBC) fly ash as the backfilling material. The goal of this research was to develop a backfilling technique for abandoned mines that will be capable of filling underground voids to a distance of 300 ft from the injection point. The studies were conducted using a glass-top physical model of cross-section 13 in. × 4 in. and length 30 ft. The material was conveyed by formation of meandering conduits. Plugs were formed in the conduits during backfilling. Air impulses knocked the plugs and cleaned the conduits for material flow. The results indicate: (1) short-duration air impulses enhance the rate and range of the fill; (2) two successive impulses are more effective than a single impulse; (3) a seven-minute interval between impulse(s) give the best results.