APPLICATION OF SHOTCRETE AT ORYX MINE

When Oryx Mine down-scaled in 1994, focus was placed on development, w ith the primary aim being the exposure and proving of ore reserves. In order to achieve this aim, development ends had to be advanced to ree f at the maximum possible rate. This in turn called for support method s which could keep up with the advancing faces, taking up minimum spac e and time for installation, while providing on the face areal coverag e and effective long-term support. In the majority of the development ends which were located in fairly competent ground, the grouted rod de velopment support proved to be adequate until such time as secondary s upport in the form of meshing and lacing could be installed. The ends developing towards the eastern boundary of the mine, especially in the 'C' block, encountered extremely adverse ground conditions due to the presence of smectite zones within the footwall quartzites. Smectites are a group of montmorillonite clay materials, mainly composed of hydr ous aluminosilicates, They occur as minute platy crystals in the rock mass and are especially notable for their ability to absorb liquids. G enerally, the zones are found in between the bedding planes of the hos t rock, and may vary considerably in thickness over short distances. W herever the smectites were exposed by the development blasting, the ro ckwalls weathered as the smectites absorbed water and the condition of the tunnel rockwalls deteriorated rapidly. When the smectites were le ft exposed and allowed to weather, it became almost impossible to inst all secondary permanent support such as meshing and lacing at a later stage. To minimise the exposure time and subsequent deterioration of t he smectite zones, it was recommended that all development ends encoun tering smectites be shotcreted as soon as possible after blasting. In developing a shotcreting support methodology, both a drycreting and we tcreting system were investigated. The situation at the time ruled out the use of a wetcreting system on the basis of the extensive and cost ly infrastructure required, as well as its limited manoeuverability. I nstead, it was decided to opt for a smaller scale but more manoeuverab le drycreting system. The system utilized a number of portable drycret e machines with prebagged cement, which could support several developm ent ends in close proximity. Initial trials using normal 30 MPa shotcr ete on 19 level proved successful and the system was implemented.