Analysis of steel wire rope mesh as roof support in underground mines

Abstract

Fatalities in underground mines due to rockfalls have significantly decreased since 1993. This is due to the improvement in underground roof support technologies, including wire mesh screens. Mine Support Products (MSP) designed and manufacture their own wire mesh made of galvanized steel wire rope. The aim of this study was to analyse the mechanical behaviour of MSP's wire mesh when subjected to an impact load. Four configurations of the wire mesh with different diameter and construction wire ropes were tested using the drop test. Drop tests were done with a 455 kg weight from various heights and the wire mesh deflection was measured afterwards. The four different configurations chosen was made of 3 mm (7x7), 5 mm (7x7) and 4 mm (1x19) wire ropes weaved in a certain pattern to form a wire rope mesh. From the drop tests it was evident that the 4 mm (1x19) inner and outer wire rope mesh performed the best. No fracture of the wire ropes occurred after a drop test height of 300 mm and the wire mesh deflection therefore still within spec. The other three configurations also performed within specification by not deflecting more than 400 mm from a drop test height of 100 mm. Therefore, MSP's wire meshes are suitable for use as roof support in underground mines. Finite Element Analysis (FEA) of the drop tests was done on three different configuration wire meshes and compared with experimental results. FEA software Ansys LS-DYNA was used. FEA of drop tests were done on the 3 mm (7x7) inner 5 mm (7x7) outer wire rope mesh, 3 mm (7x7) inner 4 mm (1x19) outer wire rope mesh and the 4 mm (1x19) inner and outer wire rope mesh. The FEA drop test results showed a good correlation with experimental results, with deflection differences between the two methods ranging from 1.1% to 18%. Von mises stress analysis also revealed that the highest stress was at the mesh attachment points. This corresponded with experimental results where fracture of wire ropes occurred at the attachment points. The corrosion behaviour of MSP's wire mesh was also analysed. Salt spray tests were done on galvanized, bitumen coated and PVC coated wire ropes. Bitumen and PVC coated wire ropes had noticeable corrosion resistance when compared to uncoated galvanized wire ropes. Galvanized wire ropes were also left in an underground gold mine for 76 days. Following this exposure, tensile tests were carried out on the corroded wire ropes and compared with the breaking strength of uncorroded wire ropes. Tensile tests revealed that the corroded wire ropes had breaking strengths 22.5% lower than their uncorroded counterparts. Therefore, corrosion had a noticeable effect on the wire rope breaking strength.