Project Details

Project Details:

As near surface ore deposits are becoming more scarcely discovered, the mining industry has turned to mass mining methods at greater depths below ground surface. The scale and depth of these mines has led to increased susceptibility to spalling and strainbursting which are modes of deformation associated with stress fracturing of brittle rock. Spalling represents more gradual deformation while strainbursting is sudden and can result in projectile velocities of rock fragments and slabs. Spalling slowly erodes the load bearing capacity of the ground support while strainbursting suddenly imposes large energy demands on the ground support systems and creates a hazard for mining personnel. Experience based ‘design’ is still relied upon heavily for most mining projects due to the lack of geological data relative to the scale of the ore bodies. Therefore, research is being undertaken to improve the assessments that can be applied to address these hazards during mining, when observations and data become available.

There are two main focuses for this research. The first is on data driven assessments that build upon observations and structured databasing of tunnel damage in mines using a novel Rockburst Damage Index (RDI, Roy et al. 2022). Figure 1 shows an example of damage mapped from a strainburst along the length of a mining tunnel using RDI and quantitative analysis of the damaged locations with respect to the geotechnical domains and profile of the tunnel. Strainbursts tend to happen in clusters, sometimes leading to spatially dispersed damage in a mine, therefore a novel approach has been developed to track local damage to the underground tunnels while utilizing semi-quantitative indices to track the overall outcome of the cluster of strainbursts on the mining operation.

Figure 1: The top left photo shows damage being mapped along the length of a mine tunnel using RDI. The top right shows the lengths of tunnels damage by RDI and geotechnical domain. The bottom shows quantitative analysis of the area of the drift profile where the most severe damage was recorded based on > 2km of damage recorded in the database (modified from Roy et al. 2022).

The second focus of the research is to advance state-of-the-art numerical simulations that can be used for back analyses and to improve ground support designs for spalling and strainbursting ground. The transition between these mechanisms is complex and is not adequately assessed using existing analytical solutions, empirical indices, or continuum models. Therefore, a hybrid continuum/discontinuum modelling approach is being researched that can properly simulate the stress fracturing process, conversion of stored strain energy into kinetic energy, and the subsequent large deformations. Figure 2 shows an example of three simulations showing the transition from spalling behavior (right side) to strainbursting (left side) for an excavation scale UCS test.

Figure 2: Simulation of a large scale UCS test using a hybrid continuum/discontinuum approach that can capture both spalling (left side) and strainbursting (right side) behaviors at the scale of mining tunnels

Reference:

Roy, JM, Eberhardt, E, Bewick, RP & Campbell, R 2022, ‘Application of data analysis techniques to identify rockburst mechanisms, triggers, and contributing factors in cave mining’, submitted June 2022 to Rock Mechanics and Rock Engineering.