Project Details

Project Details:

Brittle failure around underground excavations (e.g., spalling or strainbursting, leading to excessive bulking; Figure 1) has been a major issue in highly stressed rock. Experiences from historical and existing deep caving operations suggest that excavation damage associated with brittle failure, posing a safety hazard for workers, and causing costly interruptions to production. Consequently, effective and efficient ground control strategies need to be adopted to manage these challenging conditions (Kaiser & Moss, 2022).

Figure 1. a) Example of rock mass bulking due to stress fracturing. b) Excavation damage due to strainburst event

An innovative deformation-based support design (DBSD) approach (Kaiser, 2014; Kaiser & Moss, 2022) for brittle rock has been introduced recently to address this issue. A transition from conventional energy-based support design approaches (Hedley, 1992; Ortlepp, 1992; Kaiser et al., 1996) to DBSD for brittle ground has been implemented as a strategic element of ground control for the Deep Mill Level Zone (DMLZ) mine of PT Freeport Indonesia to improve excavation performance. The DBSD approach considers how displacement induced by stress fracturing can reduce the support capacity after support installation. As such, the DBSD approach accommodates both energy and displacement demand to be compared with the capacity remaining (remnant support capacity) rather than the initial capacity of an installed support. This type of design aspect is not considered in the conventional energy-based support design approach.

Figure 2. Integrated monitoring methodology to measure both depth of stress fracturing and the corresponding rock mass bulking

This research focuses on an advance understanding of how the depth of stress fracturing and rock mass bulking progress to increase the effectiveness and reliability of the DBSD approach (Figure 2). The DBSD parameters such as displacement trend, bulking factor (static and dynamic), and support system capacity are studied as cave abutments and stress path evolve. A methodology to calibrate and validate the DBSD parameters through dedicated monitoring stations across the production level footprint is proposed (Figure 3). Each monitoring station integrates borehole camera (BHC) surveys and multipoint borehole extensometers (MPBX) to determine the depth of stress fracturing, and convergence measurements and light detection and ranging (LiDAR) surveys to characterize the corresponding rock mass bulking.

Figure 3. Dedicated integrated monitoring stations for calibration and validation of the DBSD approach.

Reference

• Hedley, D. G. F. (1992). Rockburst Handbook for Ontario Hardrock Mines. CANMET Special Report SP92-1E.
• Kaiser, P. K. (2014). Deformation-based support selection for tunnels in strainburst-prone ground. Proceedings of the Seventh International Conference on Deep and High Stress Mining, January 2014, 227–240. https://doi.org/10.36487/acg_rep/1410_13_kaiser
• Kaiser, P. K., McCreath, D. R., & Tannant, D. D. (1996). Canadian Rockburst Support Handbook: Prep. for Sponsors of the Canadian Rockburst Research Program 1990-1995. Sudbury, Ontario: Geomechanics Research Centre.
• Kaiser, P. K., & Moss, A. (2022). Deformation-based support design for highly stressed ground with a focus on rockburst damage mitigation. Journal of Rock Mechanics and Geotechnical Engineering, 14(1), 50–66. https://doi.org/10.1016/j.jrmge.2021.05.007
• Ortlepp, W.D. (1992). The design of support for the containment of rockburst damage in tunnels – An engineering approach. Support in Mining and Underground Construction, Kaiser & McCreath (eds). Balkema Rotterdam