Abstract: To study the fracture characteristic behaviour of the defective cemented backfill, three-point bending tests were carried out on the cemented backfill specimens with the offset ratios of 0, 0.25, 0.50, 0.75 and with the seam height ratios of 0.10, 0.25, 0.50, respectively. A high-speed camera was employed to capture the full-range crack propagation, and two-dimensional particle flow software PFC2D was used to analyse the crack propagation process, the fracture mode and the fracture mechanism of the cemented backfill. The results showed that the fracture peak load increased with the increase of the crack offset ratio at the same seam height ratio. When the offset ratio was constant, the peak load was smaller with the increase of the seam height ratio. When the crack offset ratio was at 0, 0.25 and 0.50, the crack propagated from the offset, and the deflection angle increased with the increase of the offset ratio. When the crack offset ratio was at 0.75, the crack propagated from the centre. The crack propagation process was divided into three stages, and it was serrated-shaped. The fragmented particles were generated and shed during the crack propagation process. Two-dimensional particle flow model was employed to simulate the force chain network, velocity field and fracture mode of specimens. The obtained results were compared with experimental results of macro mechanics to explore the mesoscopic fracture mechanism. The peak loading of the fracture was not more than 3.8% compared with the experimental value.

Key words: downward cut-and-fill mining method, cemented backfill, three-point bending, fracture characteristic, crack propagation