Workshop & Short Course
Deformation-Based Support Design for Burstprone Mines
By Peter K. Kaiser & Ming Cai
As mines go deeper and get larger, underground excavations become more vulnerable to damage and mine designs become more fragile. As a consequence, ground control and rock support increasingly dominate construction schedules and production performance. Efficient and effective support becomes a strategic element of asset management because mine infrastructure and extraction developments are the most significant investments in a modern mine, particularly in caving operations. This investment must be protected and maintained to reduce the risk of ground failure related production disruptions (Moss and Kaiser, 2021). Furthermore, many mining companies working at great depth have identified seismic hazards as a corporate risk and consider ground control with cost-effective support systems a strategic tool in asset management.
Brittle failure processes in highly stressed ground are inevitably associated with large rock displacements and several interlinked concepts are important when assessing the health of an excavation. The support must not only be designed for load equilibrium but also for deformation compatibility. Most importantly, it must be recognized that a support’s displacement capacity is being consumed when the rock mass is deformed after support installation. Hence, it is necessary to design for the remnant support capacity at the time when the support is needed, i.e., at a critical stage of its utility rather than when it is installed. This often-dominating design aspect, at least in mining, is not accounted for in standard empirical classification systems for support design and has led to unnecessary excavation damage and production interruptions because of the need for repair of the support.
Working with the mining industry, the lead instructor has developed ‘deformation-based support design’ (DSD) principles and procedures and verified their applicability at burst-prone mines. This ‘DSD’ approach is applicable to static (or gradual) and dynamic (or violent) failure resulting from hour-glassing of pillars to strainbursts to dynamically loaded excavations in mines experiencing severe seismicity. For the later, common practices of energy-centric design without due consideration of mining-induced deformations are no longer best practices.
Finally, with rapid advances in monitoring technology, particularly displacement monitoring, new opportunities arise for safety and economic improvements in ground control. In open pits, advances in radar technology, LiDAR and photogrammetry have already revolutionized slope design by a seamless integration of displacement data with design and performance assessments. Emerging displacement monitoring technologies for digital convergence monitoring in underground construction and mining offer similar opportunities to utilize displacement records for design verification and optimization, safety assessment and preventive support maintenance (PSM).
The combination of advanced monitoring and DSD provides means to improve management of excavations in stressed ground experiencing large deformations induced by static and dynamic loading.
Coming up course:
MIRARCO—Mining, Innovation, Rehabilitation and Applied Research Corporation, founded in 1998, is a not-for-profit applied research and technical service company formed through collaboration between Laurentian University and the private and public sectors. MIRARCO serves as an innovation bridge between researchers and industry.
The Goodman School of Mines serves as the gateway to Canada’s Mining University – Laurentian University. It is your one-stop access point to the most comprehensive mining education available in Canada, with an extensive array of undergraduate- and graduate- level programs, training and research geared to the full mining cycle.
Brittle rock mass failure processes are reviewed within a framework of rock support selection for highly stressed ground. Static and dynamic failure processes are discussed and illustrated on case examples. Deficiencies in current approaches are highlighted with the intent of pointing the way forward to more rational support design methods for conditions experiencing mining-induced stress changes. This course is intended to broaden rock support knowledge for site engineers and consultants and to stimulate discussion on the above-described engineering challenges. The course covers related topics including engineering challenges of strainbursting ground.
This course focuses on support design for brittle rock when displacements induced by stress-fracturing may consume much of the support’s capacity. It deals with the functionality of the support in deforming ground and with the consequences of mining-induced support damage (e.g., during production at the footprint). If support capacity can be consumed, it can also be restored by various means of preventive support maintenance (PSM). This concept for cost-effective ground control is introduced and illustrated with operational evidence. Accounting for capacity consumption and integrating preventive support maintenance into the mine development and operation schedule provides means for prudent asset management and opportunities for cost optimization.
For these purposes, support needs to provide a safe work environment and maintain an operationally functional excavation. In particular, it has to eliminate or at least drastically reduce the likelihood for severe excavation damage. From a technical perspective, this means that the rock must be made self-supporting by creating deformable arches or wall panels that can adjust to large mining-induced deformation demands, whether inflicted by static or dynamic loading.
The course provides knowledge and guidance for the application of DSD principles in a qualitative and quantitative manner.
The following tangible benefits can be derived from de-risking operations by a successful implementation of “deformation-based support design’”principles:
- improved workplace safety through real-time monitoring of consumed support capacity;
- improvement of resilience of support system through use of deformation compatibility criteria;
- reduction of operation delays through minimization of severe excavation damage;
- reduction of rehabilitation costs through proactive support maintenance; and
optimization of ground control measures in critical infrastructure.
The course consists of five modules of which the first in presented in the form of a workshop to provide an overview of the potential benefits for mining operations and the need for change. It does not cover technical details but rather focusses on opportunities to overcome deficiencies in current practices and opportunities for safer and more cost-effective rock support strategies. Key aspects for change management when moving toward DSD and when adopting PSM procedures are introduced.
Who should attend? Engineering team members involve in mine design and mine planning, and senior operations team members involve in the implementation of ground control measures.
The remaining four modules are training modules covering the ‘how to’ and are intended for ground control engineers, technicians and consultants that are mandated to implement the DSD principles. Qualitative and quantitative means for the estimation of support demands and support system capacity consumption and for PSM implementation are covered.
Who should attend? Engineering team members involve in ground control and support design, consultants engaged in ground control, and operations team members involve in monitoring and data collection.
The course instructors have revised and significantly updated the Canadian Rockburst Support Handbook (Kaiser et al., 1996) with a much stronger focus on strainburst assessment and related damage mitigation. Volume I of this revision has been released in 2018 as a Rockburst Support Reference Book (Cai & Kaiser, 2018). Volume II focusing on strainbursting is in preparation and will be released in 2021. Preliminary draft chapters will be distributed to course participants. Related publications providing background information or details of material presented will be available in pdf format.
Cai, M. & P.K. Kaiser, 2018. Rockburst support reference book. Volume I: Rockburst phenomena and support characteristics. MIRARCO, Laurentian University, Sudbury, Ontario. ISBN 978-0-88667-096-2. Free copies available from Rockburst Support Reference Book.
Kaiser, P.K. & M. Cai, 2021. Rockburst support reference book. Volume II: Rock Support to Mitigate Rockburst Damage Caused by Dynamic Excavation Failure. MIRARCO Laurentian University (draft manuscript released 2019 and 2020).
Moss, A. & P.K. Kaiser, 2021 An Operational Approach to Ground Control in Deep Mines, CIM Montreal (abstract submitted).
Kaiser, P.K., D.D. Tannant, D.D. & D.R. McCreath, 1996. Canadian Rockburst Support Handbook. Geomechanics Research Centre, Laurentian University, Sudbury, Ontario.
Preliminary course outline
Each module involves two to three hours of presentations with active interactions presented in a virtual delivery format. As much as possible, the course material will be tailored to the needs of the participant or hosting company or to the common support technologies adopted at the operations of the attendees.
Module 1 - Deformation-based support design
- Motivation for move from common to best practice in support design
- Limitations of current design approaches
- Removal of fundamental technical flaws – ignoring support capacity consumption
- Deformation-based support design methodology – calibrated, measurable design
- Shakedown and strainburst damage
- Mechanisms of various types of strainbursts
- Strainburst assessment damage mitigation
- Support design
- Demand estimation
- Support system capacity estimation
- Support capacity consumption and preventive support maintenance
- Qualitative application using ‘gabion panels’ to create deformable support arches
- Value proposition for change in design methodology
- De-risking mine operations as drive for change management
- Practical examples of support selection based on monitoring data
- Objective of training modules
Short course with repeat of Module 1
Module 2 - Rock failure, excavation damage & role of support
- Brittle failure of rock
- Depth of failure and bulking of stress-fractured rock
- Rock mass bulking
- Rockburst phenomenon and mechanism
- Strainbursting (triggered and dynamically loaded)
- Motivation for move from common to best practice in support design Highlights of Mueller lecture)
- Excavation vulnerability and fragility
- Excavation response to dynamic disturbances
- Review of highlights of deformation-based support system design
- Engineering principles
- Rockburst support design process
- ‘Gabion panel’ support concept for stress-fractured ground
- Workflow: Design steps and high-level overview – Executive Summary
- Demonstration of design steps on support design for intersection
Module 3 - Capacities of support components (rockbolts and surface) and support systems
- Static and dynamic capacities of rockbolts
- Influence of test methods and parameter selection
- Static and dynamic capacities of surface support elements
- Influence of test methods and parameter selection
- Support system capacity (SSC)
- Overall SSC
- ‘Local’ SSC
- Support system capacity consumption
- Support system performance
- Preventive support maintenance
Module 4 – Support design analysis - Demand estimation and factor of safety assessment
- Identification of engineering demand parameters for design
- Support system demand – load, displacement and energy demand
- Static and dynamic demand
- Domaining for support selection
- Factor of safety assessment
- Overall and ‘local’
- Introduction to DSSD-tool (Dynamic Support System Design tool; prototype)
- Intersection design
Module 5 – Support selection – Dynamic Support System design and allowable ground motion charts
By P.K. Kaiser and M. Cai
- Demonstration of DSSD-tool including parametric studies
- Allowable ground motion charts
- Approach to deformation-based support system assessment
- Monitoring and ground-truthing
- Practical examples of support selection
- Discussion of mine-specific applications
- Summary of course content and qualitative application without DSSD-tool
- Value proposition: Overview of opportunities for potential immediate cost-benefits in operating mines
- Change management considerations
Prof. Peter Kaiser, Professor Emeritus, joined Laurentian University in 1987 as Professor of Mining Engineering and Chair for Rock Engineering and Ground Control at the Bharti School of Engineering. He was the founding President of MIRARCO and later was seconded to the Centre for Excellence in Mining Innovation (CEMI) as Founding Director and then as Director of the Rio Tinto Centre for Underground Mine Construction. He is a specialist in applied research for underground mining and construction and brings extensive experience from both the industrial and academic sectors and has served as a consultant to numerous consulting engineers, mines, and public agencies. He is a Fellow of the Engineering Institute of Canada (EIC) and the Canadian Academy of Engineers and in 2013 was awarded the Julian C. Smith Medal of the EIC for “Achievement in the Development of Canada”. He is the author of more than 400 geomechanics publications. In 2016, he has delivered the Muir Wood lecturer at the WTC and the MTS lecture at the 50th US Rock Mechanics Symposium, and in 2019 he presented the Mueller lecture at the ISRM congress in Brazil on a topic related to this course, i.e., on moving “From common to best practices in underground rock engineering”.
Prof. Ming Cai is the Geomechanics Research Chair in Laurentian University’s School of Engineering. Prior to joining Laurentian, he was a member of the Mansour Group Inc., MIRARCO, GRC, Tokyo Electric Power Services Ltd., and Tsinghua University and brings over 20 years’ research, education, and industry experience. He has a wide variety of interests in rock mechanics and rock engineering, and has made technical and scientific contributions to the advancement of rock engineering, including constitutive modeling of rock masses, rock mass characterization, rock support, interpretation of AE and microseismic monitoring data, and rock failure process simulation, etc. Dr. Cai is the author/co-author of over 200 publications. He is a recipient of the John Franklin Award in Rock Mechanics from the Canadian Geotechnical Society. Currently, he serves as an editorial board member for six international journals in the fields of rock mechanics and rock engineering.