Abstract

Backfill is widely used in underground mines around the world for its effective reduction in environmental impact of mining operations by utilizing a part of mine waste as underground backfill material. The strength of backfill plays a critical role in improving stop stability and preventing surface subsidence. In this paper, a series of SHPB (Split Hopkinson Pressure Bar) tests with different strain rates and static axial pressures are conducted. The results show that: (1) The dynamic strength of the backfill specimen increases first and then decreases with the increase of static axial pressure. It reaches a maximum when the static axial pressure reaches 30% of the static compressive strength in the SHPB test. (2) The stress-strain curves of backfill specimens can be divided into three stages: elastic stage, yield stage and failure stage. The compaction stage is obscure. The backfill specimens are not sensitive at low strain rate. (3)With the increase of incident energy, the absorbed energy mounts. (4) The failure mode of the backfill specimen is tensile failure when static axial pressure is 0MPa in the SHPB test while it becomes compression shear failure when static axial pressure is higher than 0MPa. (5) The backfill specimen is very compressed when it is loaded with axial stress and confining stress simultaneously. This compression property of backfill specimen may be related to the nature of hydration products at different curing times, which requires further research in the future.