Roof Behavior In South African Coal Room And Pillar Panels

An extensive underground roof-monitoring program was conducted in order to determine the roof strata behavior under various conditions. In total 29 sites at 5 different collieries were monitored using the sonic probe extensometer. Results showed that, in drill and blast sections, there are often pre-existing openings in the roof prior to the installation of the support. An estimated 42 per cent of the total roof displacement monitored in drill and blast sections took place prior to the installation of support. A comparison between roadways and intersections indicated that, for a 40 per cent increase in the span, taken across the diagonal of art intersection, relative to the roadway width, the magnitude of the displacement in the roof increased by a factor of 3. Total displacements measured were relatively small, only 2 reaching double figures of 12 mm. The remainder were all less than 7 mm. The results also showed no evidence of a substantial increase in the height of the bed separated, potentially unstable roof strata, as is the case in the high horizontal stress-driven beam-buckling mechanism experienced in for instance some Australian coal nines. Therefore, it was concluded that, in South African collieries, the effects of horizontal stresses is generally relatively small compared to overseas collieries.