Open stoping is a common mining method employed in the Canadian mining industry. Extracting large volumes of rock can present stability issues which can affect productivity and safety. Many factors such as changing stress states, rock mass structure, and intact rock strength can contribute to instability. One factor not commonly assessed when examining stope stability is exposure time. With increased exposure time, the rock quality of the opening tends to degrade. Birchtree Mine located in Thompson, Manitoba, is the focus of this study due to the time dependent instability that has been observed.
For the proposed project, an empirical method was chosen since these methods can easily be updated with future case histories to better reflect onsite conditions. Few empirical methods exist for assessing exposure time for open stope mining. The most common method of incorporating time with stability is Bieniawski’s 1989 RMR Stand-up Time Graph. As part of this project the original data used to create the RMR Stand-up Time Graph was reinterpreted so it could be plotted on the Stability Graph, which is used for open stope design.
Case histories from the Birchtree mine, along with the original database for Bieniawski’s empirical method, have been examined. Comparisons were conducted to evaluate the accuracy and validity of the Bieniawski and Birchtree data. Other factors that may affect stability and exposure time were also discussed. This research has led to the development of a new empirical design method that incorporates exposure time in the prediction of open stope stability
