The role and importance of geotechnical engineering for a mining operation (1)
- 1. 1 image source: www.abc.net.au The Role and Importance of Geotechnical Engineering for a Mining Operation Author: Dr. Alex Vyazmensky https://www.linkedin.com/in/vyazmensky/ 1. Introduction Geotechnical Engineering has become an integral part of mine operations fairly recently. Three decades ago, very few mines employed site based geotechnical engineers, geotechnical design and operational support were primarily carried out by specialized consultancies and/or research institutions. Nowadays, global mining companies develop in-house geotechnical expertise at corporate and mine levels and hire consultants to undertake mining project studies or assist in solving specific ground engineering problems. This important change was brought about by strict mine safety regulations enacted in 1990ties and gradual recognition by the mining community of the value of ground engineering in optimizing mine design and managing the geotechnical risks. While majority of the mining companies have already established geotechnical capabilities, many are yet to develop or upgrade them. This article aims to increase awareness of the role and importance of geotechnical engineering in mining. 2. Geotechnical Role within Mine Technical Services Geotechnical function on a mine site is a part of Mine Technical Services department. This department consists of several integrated functions and is responsible for
- 2. 2 strategic mine planning and effective technical guidance of the mining operations. A typical Mine Technical Services setup and key responsibilities of technical functions are shown in the figure below. It is the role of the site geotechnical engineer to provide ground engineering support to achieve mine production targets and identify opportunities to improve geotechnical aspect of the mine design. Also, an important facet of the role is to timely advise the mine management on the need to change the mine design and/or mine plan to address the geotechnical risks. 3. Geotechnical Room for Improvement in Mine Design Mine design at a project study stage is based on the information available at the time the study is carried out. Usually limited detail of the overall rock mass is available and it is necessary to make a number of assumptions on the site geotechnical conditions and characteristics. As mine develops and new geological, geotechnical and hydrogeological data is being collected, and performance of existing excavations is analyzed, it is necessary to re-evaluate design assumptions and, if required, modify the initial design. Let's consider few examples of the mine design improvements through geotechnical engineering. Open Pit Mining The value of open pit mining operation is primarily driven by ore vs. waste strip ratio. The less waste to move to extract ore, the higher the revenue that open pit mine
- 3. 3 generates. Open pit slope geometry (or slope angles) is at the core of mine design, it is determined based on rock mechanics principles by geotechnical engineers. It is in their custody to design stable slopes to produce the most value for the excavation. In a large open pit, a change of a slope angle by one degree can result in either increase or decrease of waste volume by few percent, which has a notable impact on total costs. It is worth noting that a majority of pit projects are executed on Feasibility level geotechnical design with pit slope accuracy of +/- 3 to 5 degrees. Detailed geotechnical design can have a large impact on pit mining economics. Underground Mining For an underground operation optimization of mine infrastructure and ore access layout can save hundreds of meters of UG development. Fine tuning mining method parameters (e.g. stope dimensions, lift heights) can increase a key UG operation metric - ore extraction volume per meter of development. Although it is a tough task, optimization of ground support requirements can lead to higher development rates. Each of these design improvements can increase the mine value. CONSTRUCTION OF CHIQUIQAMATA UNDERGROUND MINE, CHLE image source: www.mining.com
- 4. 4 It is also worth noting that detailed geotechnical design may arrive to a conclusion that initial geotechnical design is over-optimistic, in this case corrections are proposed to de-risk the mine plan. Opportunities to generate value in the mine design through a continuous geotechnical engineering must be fully explored. All modifications to the initial design should be supported by sound analysis carried out by a qualified and experienced geotechnical engineer. 4. Geotechnical Engineering and Risk Management A loss of the ground control due to poor consideration of geotechnical conditions at the design stage and/or a lack of proactive ground engineering during mine operations may lead to failures, here are some examples: • Bench and slope failures • Uncontrolled falls of ground • Uncontrolled subsidence • Uncontrolled caving • Rock bursts and other mine induced seismic events • Sill and crown pillar failures • Failures of stopes, ore passes or shafts • Inrushes of unconsolidated ground, back fill or water Delays caused by localized geotechnical failures defer revenue generation and disturb the planned work activities. Significant geotechnical failures can lead to a loss of access to the resource and loss of equipment, resulting in a lengthy mine shutdown and costly recovery efforts. Permanent closure of the mining operations is also possible in the event of a catastrophic geotechnical failure threatening public safety, infrastructure and the environment. Geotechnical risks resulting from a loss of ground control are real and should not be taken lightly. A lack of understanding of their impact on the mining process and/or
- 5. 5 passive approach to risk management will eventually result in unsafe working conditions and may lead to a significant reduction of the mine value. MULTI-BENCH SLOPE FAILURE @ WEST ANGLES IRON ORE MINE, WESTERN AUSTRALIA image source: http://www.geovert.com Over the last ten or so years global mining companies have adopted a unified approach to ground control risk management. Each mining operation, regardless of a jurisdiction, is required to develop and implement a site-specific Ground Control Management Plan. This framework is used to manage ground control from design to implementation and verification, this is achieved by: • Outlining a systematic approach to ground control. • Describing the process for the reporting and communication of geotechnical hazards. • Outlining the process and provide guidelines for the prediction, identification, monitoring, assessment and control of changes in the ground conditions. • Providing guidelines for the change management in the event a hazard has been identified.
- 6. 6 A mine site with effectively implemented Ground Control Management Plan will have procedures in place to assess ground behavior, proactively identify factors that may lead to unplanned ground failure and develop measures to prevent them. 5. Concluding Remarks It should be recognized that initial mine geotechnical design is carried out in the environment of pervasive uncertainty due to an incomplete knowledge of material characteristics, loading conditions and rock mass structure. Therefore, continuous geotechnical data collection and analysis are required to ensure that the mine design is based on real conditions and is optimal. Geotechnical uncertainty at the design execution stage should be managed through a site specific risk management framework (Ground Control Management Plan) to prevent unwanted outcomes or, at the minimum, mitigate their consequences to an acceptable level. The value that geotechnical engineering can add to mine planning and operational processes should not be underestimated. The mines that get their ground engineering right are able to minimize practical geotechnical difficulties and achieve efficient and safe ore extraction. THE SUPER PIT, KALGOORLIE-BOULDER, WESTERN AUSTRALIA image source: http://www.redzaustralia.com