Mining and rock engineering projects often rely on limited stress measurement data. Aalto University developed a novel method with real time access to in situ stress state to optimize mining sequence, to reduce ore dilution, to improve working safety and to limit ore losses. The method is based on real time inversion calculation of the strain data, which is obtained using intelligent bolts or extensometers. Inverse calculation of the stress change is carried out using unit stress responses and superposition. The continuous, homogenous, isotropic, linearly elastic rock conditions are assumed for the rock mass and numerical modelling tools are used to generate the stress responses. Blind test challenges for the method were carried out to predict the robustness of the method in mine-like conditions. In synthetic tests the method performed well with good precision. Boliden's Kylylahti mine has been instrumented and the analysis of the data is being carried out.
Mining and rock engineering projects often rely on limited stress measurements carried out at certain stages of the project. In number of cases previously, the stress state has been monitored during the excavation, however with significant amount of effort and using expensive stress measurement cells (Kaiser et al. 2001). However, strain measurements are a cheap and widely used method in the mining industry to monitor the rock mass response to mining (Shen et al. 2008 and Bergström et al. 2014). A method for estimating the in situ stress change around an excavation in elastic rock was developed and is presented in this paper. The estimation is based on real time strain data, obtained using extensometers or intelligent bolts.
Online and real time access to in situ stress state can be used to optimize the mining sequence, to reduce ore dilution and to limit ore losses. It can also support more precise reinforcement design and give the ability to detect and to react to unexpected changes while maintaining a higher level of safety and avoiding collapses. Stress state change monitoring is able to give feedback about the success of mining sequencing and sufficiency of ground control methods. With the real-time monitoring of the stress state, it is possible to increase the safety of underground mines especially if the stress changes cause significant risks.
