A new virtual short course series with four modules on “Deformation-based support design and Rockburst hazard assessment”
Presented by P.K. Kaiser (GeoK Inc), M. Cai (MIRARCO) and D. Malovichko (IMS)
Delivery dates and times: March 6&7 and 21&22, 2023 – 4:00pm to 8:00pm EST
This course focuses on support design for excavations in brittle rock when displacements induced by sudden stress‐fracturing (strainbursting) 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 and offers quantitative means to estimate the capacity of integrated support systems and a systematic approach to compare it with the static and dynamic demands imposed on the rock support.
Preventive support maintenance (PSM) is introduced as a cost‐effective ground control and supported with operational evidence. Accounting for capacity consumption and integrating PSM into the mine development and operation schedule provide means for prudent asset management and opportunities for cost optimization.
Sudden stress‐fracturing of excavation walls emits seismic waves that can be used to identify the depth of strainbursting and the duration of the related rock mass bulking process. This provides essential input for support design in strainburst prone ground, which is a new focus of this course.
COURSE DETAILS AND REGISTRATION COURSE MATERIAL
The rockburst hazard in strainbursting ground depends on the stress level (stress at mining stages and strength in geological domains), the amount and rate of sudden stress fracturing, the intensity of ground motion, and the amount of consumed support capacity (co‐seismic and mining‐induced strain). These and other factors are used to establish the current and to forecast the anticipated rockburst hazards. This is another new focus of this course.
Deformable pillar wall support in strainbursting ground with laterally deformable ‘gabion panels’ (Photo: courtesy PTFI)
Common practices are not necessarily best practices when judged from an economic or workplace safety perspective. As in other engineering disciplines, it is necessary to systematically improve engineering design practices. This lecture addresses some deficiencies in common practice that may lead to flawed or ineffective rock engineering solutions. More than ever, as we go deeper in underground construction, are rock engineers challenged by a number of opportunities that exist for improvements. In the past, common practices that worked well at shallow depth may need to be replaced as the rock mass behavior has changed and poses new hazards at depth. This lecture focuses specifically on opportunities resulting from better means to assess the vulnerability of excavations, to characterize the rock mass, for ground control, and rockburst damage mitigation. Theoretical considerations and field observations are used to justify the proposed changes and highlight practical implications and benefits. In the spirit of Prof. L. Müller, this lecture aims at pointing the way to future improvements in rock engineering, i.e. ‘im Felsbau’, and offers guidance on how to move from common to best practices.
For the economic and safe construction of deep tunnels, a contractor has to be presented with efficient and effective support systems, i.e., support classes that can be rapidly installed and are effective in managing stress-fractured ground. For this purpose, it is necessary to properly anticipate the actual rock mass behaviour and to provide flexible but reliable means of ground control. In mining, mining-induced stresses changes further damage rock near excavations and excessive rehabilitation often causes undesirable delays and costs. In these situations, a deformation-based support design approach is needed to prevent overloading of the rock support system by excessive deformations and to sequence the support installation for optimal support performance.
In practice, robust engineering approaches have to facilitate cost-effective construction processes by ensuring that all construction tools work well. Within this framework, the lecture will focus on four technical aspects and the author draws on experiences in deep mining and Alpine tunnelling. Findings from collaborative research and “real world” experiences are merged to highlight sound engineering design practices that respect the reality of construction and the demand for workplace safety.
In the spirit of the conference theme of the 50th US Rock Mechanics Symposium, this lecture addressed one of many prerequisites for “exciting advances in rock mechanics”, i.e., the need to fully comprehend the rock mass behaviour before solving “practical issues” in rock engineering.
In most engineering fields it is possible to select the best fitting, artificial materials for a given engineering solution. In rock engineering however, a misfit between the behaviour of a natural material, the rock, and a chosen engineering solution often leads to serious complications with costly project delays or rehabilitation works and sometimes with unacceptable safety risks.
Proper rock engineering means to fit the engineering solution to the actual rock mass behaviour! Overcoming the challenge of matching the rock behaviour with meaningful engineering models and design parameters is therefore a prerequisite for advances in rock mechanics and for successful rock engineering. This lecture highlights some recent advances in understanding rock mass behaviour for the design and construction of underground excavations.
Rock mass characterization for deep underground construction and mining offers many challenges. This lecture builds on a paper presented at the 2015 ISRM Congress in Montreal. It first describes some of the key challenges when characterizing rock and then offers guidance on how to arrive at reliable rock mass strength parameters for the engineering design of deep underground excavations.
The limitations of various available rock mass classification systems, developed for excavation stability assessments and support selection, and rock mass characterization systems, developed for the purpose of rock mass strength determination, are also briefly discussed.
The main part of the lecture deals with rock mass characterization for strength determination and on practical implications for the design of deep underground excavations. It is illustrated how common practices in the use of available rock mass characterization systems often tend to underestimate the rock mass strength, particularly when well confined at depth. Improvements to currently adopted approaches are presented to help overcome these challenges. The practical relevance of reliable rock mass strength determination is illustrates by case examples from civil tunnelling and mining applications.