In our last post, we delved into mine sequencing and production scheduling, tools and strategies to achieve the production goals while meeting the constraints. Now, let's look at monitoring, evaluating, calibration and the importance of continual updating throughout the life of the mine.
Economic success over the life of a block cave mine relies on continuous monitoring and evaluation of the operations so that the production schedule can reflect changes for implementation.
A production schedule is a plan, not the reality of a mine in operation. Things happen. Unplanned upsets introduce variabilities a plan might not have anticipated. A successful medium- and long-term plan depends on continuous monitoring once operations commence, so that as unforeseen events arise, operators have time to adjust. Simulation optimization methods can help to achieve more reliable mine plans.
Safety and Sustainability
Block caving presents geotechnical hazards that require risk and safety monitoring to maintain a sustainable operation. Internal instrumentation monitoring pore pressure, stress, deformation, load, and cave propagation can provide insight into the internal stability of the rock mass as well as provide indicators of potential failures. Key internal instrumentation might include Multipoint Borehole Extensometers (MPBX), in-place inclinometers (IPI), time domain reflectometry (TDR), seismic monitoring, open borehole cameras, Networked Smart Markers, instrumented rock and cable bolts, embedment strain gauges, borehole and New Australian Tunnelling Method (NATM) pressure cells, borehole stressmeters, and piezometers.
External instruments are used to corroborate the internal deformation and stress information and to monitor the topographic surface. External instrumentation includes tape extensometers, laser distance sensors, prisms, crackmeters, LiDAR laser scanners, and satellite interferometric synthetic aperture radar (InSAR).
These combined technologies provide improved insight into mining-induced ground responses, greater transparency in managing risk, numerical model calibration, and indicators needed to ensure that the cave is operating at the highest level of safety and productivity.
KPIs and KVIs
Over the life of the mine, block caving can be highly efficient economically after the initial capital investments for underground infrastructure. That efficiency, however, relies on continuous monitoring throughout operations so that adjustments can be made to the production schedule as needed.
Production rates must be monitored, along with grade control, processing recovery, quality, quantity, mine efficiency, productivity, and actual operating cost versus estimated costs in the plan. A production schedule assumes that certain key parameters are constant, but many parameters represent probabilities. For example, development rate defines the maximum feasible number of drawpoints to be opened at any given time within the scheduled horizon, this is often adjusted depending on the rock mass stress regime in which construction will take place. Drawpoint construction sequence (the order in which the drawpoints will be constructed) is also a function of the undercut sequence.
Planning for maximum opened production area at any given time depends on infrastructure and equipment availability as well as on ventilation resources. Many active drawpoints might encounter serious operational problems such as excessive haulage distance and problems related to the movement of equipment within the active drawpoints.
Draw rate, a function of the fragmentation and the cavability model, limits the production yield of a drawpoint at any given time within the production schedule. The draw rate should be fast enough to avoid compaction and slow enough to avoid air gaps. Draw rate can be calibrated based on the historical production of drawpoints in a given rock mass.
Draw ratio defines the relationship of extracted tonnage between one drawpoint and its neighbors and controls the dilution entry point and the damage of the production level due to induced stress. Adding technical constraints to the scheduling model for a desired production target within a range allows flexibility for potential operational variations.
Fundamental geomechanical, fragmentation and geological models are used to determine planning parameters such as structure, stress distribution, lithology and mineralogy. A reconciliation model captures the production performance of the mine and provides feedback of key performance indicators to the fundamental models to calibrate their behavior. This model is also used to check the validity of different assumptions included in a production schedule. As such, it can guide a mine’s production planning based on historical performance.
Simulation can increase predictability and confidence of the mine plan, it evaluates the schedule without executing it, finding the areas of concern and mitigating the risks within an optimum plan. The 3DEXPERIENCE in Dassault Systèmes can apply simulation to different steps of the mine to mill lifecycle.
GEOVIA PCBC software provides block cave modules that help users visually see dynamic mechanisms in play. For example, advanced flow modeling in the Cellular Automation in 3D (CA3D) and Marker Mixing act as post-processors to the PCBC Scheduler providing alternative flow models to help determine the best model for changing situations. The Cave Management System (CMS) optimizes and automates draw control to improve productivity. GEOVIA PCBC offers the industry’s most powerful, versatile and proven tool for block cave mining optimization.
Draw simulation in PCBC: comparing different scenarios
This was the last article of “Let’s Talk Block Caving” series. You can find the previous articles of this series in our GEOVIA User Community: New Future for an Old Idea, First Step, Right Fit?, Footprints and BHOD, Material Flow, Mine Sequence and Production Schedule.
We hope you found these articles useful. You can now learn more about the PCBC offer and block cave mining roles:
Firouz Khodayari is an industry consultant, author, and professional engineer with a PhD in mining engineering and more than a decade of international mine planning and optimization experience. He specializes in mathematical modelling and production schedule optimization for open pit and underground mining
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