A physical and numerical modelling investigation of the roadway stability in longwall mining, with and without narrow pillar protection.

Driving a supply gate in the presumed low-stress zone adjacent to the loader gate of an excavator panel led to an extensive roof fall at Bilsthorpe colliery, UK, in 1993 and left a question-mark over the use of skin-to-skin drives supported mainly by rock bolting. Physical and numerical models have demonstrated the potential danger of the working method. A shear failure plane developed from the rib edge into roof strata of the loader gate and another at the abutment side of the supply gate, exposing it to the fall of large blocks of rock. Modelling showed that the roof fall was due not to the inability of the rock bolts to prevent bed separation but to a method of working that made the bolts ineffective due to the height of the block delineated by the shear failure planes. Further modelling found that a 7.5 m or 10 m wide pillar would have prevented development of the failure zones, whereas a 5 m pillar was undersized.
Driving a supply gate in the presumed low-stress zone adjacent to the loader gate of an excavator panel led to an extensive roof fall at Bilsthorpe colliery, UK, in 1993 and left a question-mark over the use of skin-to-skin drives supported mainly by rock bolting. Physical and numerical models have demonstrated the potential danger of the working method. A shear failure plane developed from the rib edge into roof strata of the loader gate and another at the abutment side of the supply gate, exposing it to the fall of large blocks of rock. Modelling showed that the roof fall was due not to the inability of the rock bolts to prevent bed separation but to a method of working that made the bolts ineffective due to the height of the block delineated by the shear failure planes. Further modelling found that a 7.5 m or 10 m wide pillar would have prevented development of the failure zones, whereas a 5 m pillar was undersized.