Testing and Analysis of Welded Steel Wire Mesh used For Surface Rock Support
Rock Engineering 2009 - Rock Engineering in Difficult Conditions
Ellen Morton, Alan Gordon Thompson,
Welded and woven steel wire mesh or screen restrained by rock bolts and plates remains widely used for surface support of rock in underground mines. The main function of the mesh is to retain rock fragments that separate from the surrounding rock mass. The fragments may detach due to gravity and remote seismic loadings or following violent failure of the near surface rock mass due to the induced high stresses exceeding the rock mass strength.
Despite several testing programs at organisations located throughout the world, the factors that control the performance of mesh remain largely unquantified. The major problems associated with testing of mesh are the size of the samples, the restraints and loading area. The size of sample normally tested is related to typical bolt spacings less than 1.5m. It has been found that mesh restrained by plates and bolts always results in gross slip of the mesh prior to failure being produced in the wires or welds. On the other hand, “rigid” restraints at the edges of the small mesh sample do not represent in situ conditions where the boundary conditions can range from unrestrained at a free edge to flexible restraint in the middle of a large mesh sheet. With regard to loading, it may be a rigid block of irregular shape or an assembly of rock fragments. Laboratory testing cannot hope to simulate all the different situations that result in underground applications.
Therefore it was proposed previously that the best way to assess the performance of mesh is to be able to analyse the mesh using sophisticated computer software capable of simulating the various restraint and loading conditions. Such software has been developed recently. The software is capable of simulating non linear wire behaviour, rupture of wires and welds, rigid and flexible restraint and displacement and force loadings. The software has been used to complement a laboratory test program where different restraint and loading conditions have been investigated. The computer program capabilities and testing program are described in detail. The results from the laboratory testing and computer simulations are presented and compared. The results show that the computer program is capable of reasonable predictions for the performance of the mesh in the laboratory tests. Therefore, it is anticipated that the software can be applied to simulations of the complex configurations of mesh, restraints and rock mass loadings associated with underground applications and used to identify future improvements for the specifications of welded steel wire mesh.
Ground support, Analysis, Testing, steel wire mesh