STUDY OF THE INFLUENCE OF BACKFILLING ON STABILITY AND LOCATION OF REMAINING STOPES IN SILL PILLAR RECOVERY

To extract steeply dipping orebodies, many mines in Canada have adopted the sublevel stoping method, such as blasthole stoping (BHS) and sublevel longhole retreat (SLR). In such methods, sill pillars are initially kept in place to support the weight of the overburden in underground mining After the stope mining is complete, the stope voids will be backfilled with cemented rockfill (CRF). The strength of the CRF affects the stability of the adjacent stopes in the sill pillar recovery excavation scheme. Sill pillar recovery may cause prolonged failure, fatality, and equipment loss. Choosing a rational location of the last mined stope in sill pillar recovery can effectively eliminate the possible instability caused by the sill pillar recovery process. This paper uses the Finite Element Method (FEM) to present a comparison of sidewall swellings, floor heaves, and the roof subsidence of the crossing cuts in each stope among different last mined stope location scenarios. At all the 21 location scenarios, most of the roof corner displacements in undercuts are less than 10 cm, while in the overcuts, all the displacements in roof corners are over 10 cm. The values of the floor heave in the overcuts are more than 7 times that in the undercuts. Roofs in both undercuts and overcuts are prone to failures. Floors in the undercuts are more stable than the floors in the overcuts. For the optimum location of the last mined stope in sill pillar recovery, the last mined stope should be at least four-stope-width away from the two sill pillar edges.