Fifteen considerations for operational dig designs in open cut mining

In the dynamic world of open cut mining, effective dig design is pivotal for ensuring the safety, efficiency, and productivity of mining activities. For engineers tasked with creating and maintaining long-term, medium-term, and short-term dig designs, the challenge lies in balancing numerous factors to achieve optimal performance while adhering to regulatory and environmental standards.

As Atlantech Senior Mining Engineer David Shirley explains, unlike initial mine design – which focuses on feasibility and high-level planning – dig design within the operational phase requires a detailed approach that adapts to ongoing conditions and operational realities.

In the following article, David lists fifteen key considerations for operational dig designs in open cut mining.

1. Slope hazards and geotechnical consideration

The stability of slopes is a critical factor, which influences safety and operational efficiency. Engineers must have a comprehensive understanding of the mine’s geotechnical reports and characteristics, considering both natural and induced factors that can lead to failures. Geotechnical assessments guide design decisions, ensuring that slope angles and benches are optimised for long-term stability.

2. Regulatory commitments

Consideration of regulatory commitments should always form part of operational mine design checklists. The design should account for future rehabilitation efforts, including the placement of topsoil stockpiles, spoil dumps, and the configuration of final landforms. Forward planning ensures that ongoing operations align with broader environmental and regulatory compliance.

3. Designs that flow from long-term, to medium-term, to short-term

Ensuring continuity and coherence across different planning periods is crucial for operational success. Long-term plans should seamlessly transition into medium-term and short-term designs, with each phase building on the previous one.

As designs progress from long-term to short-term, the level of detail should increase to address the specific demands of stakeholders at each phase. This approach ensures all phases are aligned and integrated, fostering a smooth progression from strategic vision to practical implementation.

Long-term designs such as the overall pit shell usually undergo far more scrutiny and review from geotechnical engineers and resource geologists. Approval for these designs or any subsequent changes made to them are usually granted by senior leadership due to the elevated safety and economic risk factors. Adherence and compliance with these designs is of utmost importance for any engineer designing an adjoining medium-term or short-term design.

Additionally, it is essential to acknowledge that feedback from mine planning engineers regarding the quality and strategy of the designs should be allowed to flow back from short-term to long-term plans. This feedback loop helps refine and improve overall design strategy and execution, ensuring that insights gained from short-term and medium-term phases inform and enhance long-term planning.

4. Geological characteristics

The nature of the dig area floor, including grade, undulations, faults, and other geological characteristics, affects equipment performance and overall mine efficiency. If a dig floor on a coal roof for example, included a well-defined gully, the engineer should consider using a combination of a higher resolution of points in the design surface and clear labelling of the area on any plans produced for the workforce. Faults and dykes are usually well-modelled through exploration and blasthole geophysical logging programs. Accurate designing and effective communication around these structures empowers production teams to make good operational decisions on the fly. Accuracy in defining the structure’s boundaries is also important for reserving purposes. In the case of a dyke, the zone around the structure where ore quality is affected is known as the ‘dyke alteration halo’ or ‘dyke contact zone’.

5. Interaction with underground workings

When an open cut mine interacts with underground operations, the designer must consider potential adverse impacts such as localised subsidence, mining methods of equipment on partially extracted orebodies and access into areas with complex geometry.

6. Inundation and inrush risks

Inundation from water contained in underground workings or tailings storage facilities poses a significant risk to a mine’s safety and operational viability. Operational mine designs must include measures to prevent inrushes of water into the pit, such as establishing inrush control zones. Control zones can take on a proximity-based approach whereby the closer the operation gets to the hazard; the more rigorous control measures are enforced.

7. Straight lines make great mines

Simplicity in design often leads to operational efficiency. Straight walls make for simpler drill and blast patterns. This leads to better blasting performance and in turn, better productivity overall. Straight walls also mean straight haul roads which reduce the complexity of vehicle movements, minimise fuel consumption, and enhance safety. The principle of “straight lines make great mines” should guide the layout of roads, ramps, and dumps wherever possible.

8. Hot ground mining

In areas where elevated temperatures are encountered, specific design considerations are needed to manage risks. These might include the addition of labelled exclusion zones or heat maps with the assistance of UAVs equipped with FLIR camera equipment. Dig designs may need to be large enough to include a water-filled tyre bath on the exit lane of the dig area to manage haul truck tyre temperatures.

9. Lessons learned from previous areas

Reconciliation of previous mining areas provides valuable insights that should inform future designs. Analysing what worked well and what did not, can help engineers refine their approach, avoid past mistakes, and build on successful strategies. Continuous learning and adaptation are key to improving mine design over time.

10. Equipment characteristics

Understanding the capabilities and limitations of the mining fleet is essential in designing effective dig areas. The design must accommodate the size, reach, and manoeuvrability of the equipment to ensure safe and productive material extraction. For instance, larger shovels may require wider dig areas, while specific haul trucks might need broader turning radii when spotting under the loading equipment. Additionally, the width and floor grade of dig areas should align with the equipment size and capabilities, ensuring that access ramps and dropcuts are practical and conducive to optimal equipment productivity. By closely matching the design to machine capabilities, the overall efficiency and safety of the operation are significantly enhanced. Designs should consider the need for multiple access points to avoid bottlenecks and ensure continuous operations in case of access ramp stoppages.

11. Drill and blast

Operational dig designs should only be published for execution after a comprehensive understanding of the blasting activities in the area is understood.

Factors to note include:

• The dig design must only exist within blasted ground. Confirmation of the blasted ground perimeter can be obtained through clear communication channels with the drill and blast engineer or well-established surveying processes.
• If the dig design is in proximity to adjacent blasting activities, it is essential to adhere to site requirements of leaving buffer zones to reduce the risk of digging into a loaded blast.
• In difficult operational or geological conditions, the target blasting horizon is not always achieved. The designer must reconcile any troublesome areas and identify potential locations of hard toe.

The heave profile of blasts plays a significant role in determining equipment productivity.

Certain types of machinery perform better with specific heave profiles, while others are more versatile and can adapt to varying conditions. The blast design should be tailored to optimise the interaction between the heave profile and the available equipment, ensuring productive mining techniques and reducing wear and tear.

12. Water management

Effective water management is essential for maintaining operational efficiency and safety. The design should include provision to accommodate pumps and drainage systems that prevent water accumulation, manage runoff, and control sedimentation. Effective water management reduces the risk of equipment bogging, maintains road integrity, and minimises environmental impacts.

13. Design visual standards

Consistency in visual design standards helps ensure that all stakeholders, from engineers to operators, understand the intended outcomes. Clear and standardised visual representations of plans, sections, and 3D models enable better communication and reduce the likelihood of misinterpretation during implementation. Things like colours of string and surfaces, or colours and font of labels and text should all be standardised to promote clarity and consistency.

14. Design communication standards

Effective communication of design intentions is crucial for successful execution. Establishing clear standards for how designs are communicated – including the use of consistent terminology, documentation formats, and review processes – helps ensure that everyone involved is on the same page.

15. Communicating through high precision mining systems

Leveraging high-precision mining systems enhances the accuracy of design implementation. These systems allow for real-time monitoring and adjustments, ensuring the design is followed precisely and that any deviations are quickly corrected. This leads to better alignment with the long-term strategic plan.

Conclusion

Operational mine design in open cut mining is a complex and dynamic process that demands meticulous attention to a range of critical factors. From managing slope stability and equipment compatibility to addressing water and inundation risks, each element plays a vital role in ensuring the safety, efficiency, and productivity of mining operations. The integration of detailed short-term, medium-term, and long-term designs is essential for aligning operational realities with strategic objectives. By fostering a continuous feedback loop and adapting designs based on lessons learned and evolving conditions, mining engineers can enhance their approach and drive continuous improvement. A well-rounded and responsive design strategy not only mitigates risks but also supports the overall success and sustainability of mining operations.

We are here to help

At Atlantech, we are experienced at providing dig design services in open cut mining. Our team of experienced mining engineers can assist at identifying and planning for technical and operational challenges that may arise across every stage of the mining life cycle. Please contact us for a confidential discussion about how we can help.