Innovative ground support agents, in the form of membrane covers, have been developed in Canada and tested internationally for the purpose of partially replacing the screen component of bolts-and-screen or thin shotcrete layers in mines. One polyurethane-based, spray-on rock lining material, designated Mineguard TM, has been developed and tested primarily for use in underground hard rock mines for provision of rapidly-deployable area support coverage. Information is presented which summarizes assessment trials of the preand post-yield characteristics of rock and concrete materials subjected to large deformations when tested uncoated and coated using varying layer thicknesses of Mineguard TM. Tests were conducted for the purpose of assessing the capabilities of thin support liners to enhance the ultimate strength of rock materials, to stabilize uncontrolled, post-yield deformation behaviour and to enhance strain energy storage capacities of failing rock mass structures. In these laboratory trials, Mineguard TM surface coatings, at thicknesses of 1 to 3 mm, have been shown to beneficially enhance rock strength and other physical properties in medium to strong rock materials. Additional information, obtained from selected mine sites, is presented to validate the significant potential that such surface reinforcement agents have shown in terms of ground support capability. Experience gained by mine operators who are currently investigating the high speed application of Mineguard TM coatings, and comparison of wide-ranging laboratory response tests, indicate that this or other forms of flexible, sprayon, membrane support coverings may be able to add to or replace components of current support technologies that are required for mining safely in hard rock environments.
A variety of passive area support techniques have been applied by the mining industry to restrict the movement of loose and broken rock fragments which form about excavation rock surfaces. Typical area support techniques currently used by the industry include bolts-and-screen and shotcrete materials. Such support techniques are often used interchangeably or in combination for a variety of ground support roles, though they are known to develop support resistance in widely differing fashion.
Bolt-and-screen materials, such as weld mesh or chain link fabrics, are able to offer support resistance only after significant displacement of broken rock fragments and solely as the result of mobilized screen tension.
Shotcrete, in thin layer (5-10 cm) surface coatings, is able to mobilize resistance against small rock movements largely by its compressive and shear strength properties. Fracturing and failure of nonreinforced shotcrete linings, and loss of effective structural support, can develop when rock movements of as little as several millimetres occurs. Meshor fibre-reinforced shotcrete, alternately, can resist rock displacements of tens of millimetres before failing.
To bridge the perceived gaps in support capabilities which exist between the two dominant forms of mine area support, and to address the technical needs of the modern mining community, alternative area support techniques have been investigated. One technique which has been pursued in Canada comprises a spray-on polyurethane coating a
