The influence of roadway backfill on the coal pillar strength by numericalinvestigation

Stability of coal pillars and immediate rock mass is of importance in the bord and pillar extraction method underlying critical surface infrastructure. This paper describes the influence of roadway backfill on the coal pillar stability. Based on over 120 numerical models of various pillar height and backfill percentage, it is indicated that the pillar strength will increase with increasing roadway backfill, while the increase in pillar strength is greater for tall pillars than squat pillars for both cohesive and non-cohesive backfill. Modelling suggests that cohesive backfill is more effective in increasing both peak and post-peak pillar strength than non-cohesive backfill. It is also observed that the post-peak response will change from softening to hardening at a certain percentage of either cohesive or non-cohesive backfill.