Grant: Discovery Grants Program - Individual

Stand-up time is the time that an un-supported tunnel would remain stable after excavation before it collapses. In underground mining and civil tunneling, the stand-up time is closely related to design and installation of rock support systems near tunnel advancing faces. If the stand-up time can be assessed accurately, it is then possible to optimize the excavation cycle and increase the tunnel advance rate considerably. Unfortunately, the current method of estimating stand-up time is still based on the method proposed by Bieniawski in 1976, which shows a large uncertainty in stand-up time prediction. The challenge in this research is to better understand the behaviour of rock mass and provide solutions to assess stand-up time of tunnels excavated in rock masses more accurately. Based on the need to advance knowledge in rock mechanics and mining science, we propose to study the phenomenon of time-dependent rock failure, understand the mechanisms that govern stand-up time, develop a time-dependent rock failure model and verify the model using laboratory and field data, study how rock support enhances stand-up time, and apply the result to underground mining. The approach to be adopted is a combined application of experimental and field observations and numerical modeling using advanced numerical tools. Stand-up time of tunnels excavated in jointed rock masses will be calculated and new charts for stand-up time estimation considering factors such as excavation span, rock mass quality, overburden depth, and excavation shape will be developed. Many mines apply shotcrete immediately after scaling in an excavation cycle. The effect of shotcrete on stand-up time enhancement will be studied quantitatively in this study. The research findings from this study can contribute to a better understanding of the fundamental problem of time-dependent behaviour of rocks and provide a tool for the mining and civil tunneling industries to estimate stand-up time more accurately. The potential cost-benefits of this investigation are significant because it provides Canadian mining companies a useful tool to make important decisions related to rock support in tunnel development so as to improve safety and productivity.