The use of shotcrete in Canadian hardrock mines has experienced rapid growth over the past 10 to 15 years. In some cases the introduction of shotcrete has helped to extend the mine life or has reduced rehabilitation costs and production delays. While shotcrete is now accepted as a viable support option, there is increasing evidence that better guidelines are needed to ensure appropriate (cost-effective) selection and application of different types of shotcrete in widely differing underground environments.

The Geomechanics Research Centre has been involved in numerous field and laboratory investigations of shotcrete performance and is working towards establishing guidelines to assist the mining industry in selecting the most appropriate type of shotcrete or support system for a given application.

A zone of failed rock usually develops around excavations at depth or in highly stressed ground. This failing rock dilates and bulks in volume as it fails. Support systems designed to control the failure process and to maintain stability and safety in the excavation must be able to accommodate these deformations. Hence, much of GRC's testing has focused on the performance of shotcrete under large imposed displacements.

Loading of the shotcrete may occur very rapidly in rockburst situations or gradually over time when progressive failure processes dominate the rockmass response near the excavation. From numerous tests on shotcrete with various loading rates (pull tests, impact tests, and explosive loading) much needed data about the capacities of shotcrete under field and large-scale testing conditions has been generated. Some of the findings include:

• Contrary to results from tests on small-scale shotcrete beams, GRC has found that mesh-reinforced shotcrete offers more toughness and higher load carrying capacity than steel-fibre reinforced shotcrete at very large imposed displacements.
• Preventing excessive tangential stresses in the shotcrete is necessary for optimal shotcrete performance in excavations that will experience large convergence or closure after the shotcrete is applied.
• Shotcrete can retain its functionality near large production blasts. Shotcrete (plain, steel fibre, or mesh reinforced) can survive peak particle velocities in the order of 1 to 2 m/s as long as the underlying rock is not forcibly ejected into the excavation and the shotcrete is applied as panels that are not highly stressed.
• The addition of shotcrete to mesh greatly improves the mesh's load carrying capacity and results in a retaining component that has superior energy absorption properties.