The effects of high temperature on the compaction behaviour of waste rock backfill materials in deep coal mines

To study the mechanical properties of backfill materials during compaction at high ground temperature in deep backfill mining, the WAW-1000D electro-hydraulic servo universal machine was used to conduct compaction testing of crushed sandstones heated to different temperatures. The stress-strain curves of crushed sandstones with four particle sizes heated to different temperatures were obtained. In this way, this study analysed the influence of temperature on the stress-strain relationship, porosity changes, and deformation mechanisms during the compaction of crushed sandstones. The experimental results demonstrate the following: (1) At the same particle size, with increased heating temperature, the strain in crushed waste rock decreased at a given applied stress. (2) After heating to the same temperature, the final strains in crushed waste rock samples of different particle size distributions decreased with particle size. (3) As heating temperature increased, the porosities of crushed waste rock samples heated to 100 degrees C, 200 degrees C, 300 degrees C, and 25 degrees C are ranked thus (in descending order) at the same stress. (4) After compaction of the samples at 25 degrees C, the number of large blocks decreased, while that of smaller blocks increased slightly. After compaction of heated samples of crushed waste rock, the amount of large blocks gradually reduced, while that of medium- and small-sized blocks gradually increased with increasing temperature. The temperature affects the deformation mechanisms during compaction of the samples of crushed waste rock, thus affecting their stress-strain relationships and porosity.