Terry Fairbanks Member Name
Senior Engineer
Moving earth is big business. In fact, bulk earthworks are a way of life for the mining industry. And never is it more critical than during mine expansion as actions taken during mine expansion could have a significant impact on future mine reclamation requirements. For example, companies must adhere to strict requirements for soil management and account for material classification to determine appropriate impact on the future use for when the mine reaches the reclamation stage. The goal is to use the materials effectively and move them efficiently to reduce the significant cost associated with moving bulk volumes. This requires thorough planning and careful execution.
Cost factors affecting bulk earthworks
There are many cost factors associated with bulk earthworks. Mining expansion and reclamation projects typically try to minimize the distance material must move to minimize costs. Decisions made during mine expansion projects in terms of material placement can have significant impacts on mine reclamation costs, and yet mine reclamation costs are often overlooked when assessing proposed mine expansions. When considered holistically in the context of the mine life cycle, the impacts that mine expansions have on mine reclamation costs can influence the mine’s decision on whether to pursue or alter a proposed mine expansion to mitigate potentially significant incremental mine reclamation costs that will be incurred as a result of the expansion. Numerous factors must be taken into consideration when estimating mine reclamation costs associated with bulk earthworks using the same care that is given to analyses of mine expansions, including, but not limited to:
- The volume of earth to be moved for reclamation
- The size of the earthmoving equipment
- The distance each load needs to travel
- The time required for each trip
- The hourly cost to run each piece of equipment
- Operational costs and efficiencies
Reclamation costs associated with bulk earthworks can escalate quickly, so companies need to carefully plan the most effective way to execute the work. Traditionally, engineers are tasked with calculating and estimating costs, but their insight is somewhat limited to their own experience and can often be too high-level to accurately estimate bulk earthworks costs associated with reclamation.
With today’s technology, however, more accurate outcomes are possible. Models that employ least-distance methods can help mine owners manage bulk earthwork operations in more cost-efficient ways. One way to optimize efficiency in this regard involves a combination of 3D CAD software and algorithms.
The best way to illustrate this is through a real example of Golder’s work with a large client.
Suggested approach ‘least-distance method’
The client in this scenario was considering an expansion of their mine. They therefore needed to regrade and balance the earth within their waste rock dumps (WRDs) on a massive scale. The volume of earth to cut, transport, and fill WRDs to an approved post-mining configuration was approximately 84 million cubic yards.
The client wanted to calculate what it would cost to use their own mining fleet to move the material versus hiring an external contractor. The objective was to determine the least-cost scenario for mine reclamation.
Golder used the following methods to assist the client:
- CAD and modeling software were used to create isopach contour maps of the mine’s footprint. The maps were discretized into 75-square-foot blocks to analyze the levels of cut and levels of fill needed in each region.
- Cut-to-fill algorithms were created using C++ code to map material movement from areas of cut to areas of fill by minimizing the 3D straight-line distance that material is moved. This smart algorithm worked by disbursing cut volumes into fill locations via the most efficient routes that result in balanced cut and fill volumes.
- Volumes and hours were assigned to specific equipment to estimate productivity-based costs by task, including factors such as equipment sizes, material properties, operator experience, haul road layouts, and site-specific constraints, among others.
- Numerous iterations were carried out to find the combination that was both operationally feasible and which cost the least with each subsequent iteration attempting to improve upon the previous one.
Using this method, the client was able to gather much more accurate data and better understand the pros and cons of each reclamation scenario on which to base their decision while reducing engineering costs compared to traditional methods.
Taking the data into account, the best predictive outcome was a combination of both the mine fleet and the contractor. There was a clear cost benefit to the contractor fleet being used for the dozer portion of the regrade, and the mine fleet being used for the truck/shovel portion.
This approach helped to minimize anticipated truck haul regrade costs while leveraging the contractor’s familiarity with fine dozer grading required for reclamation.
Other industries that can benefit
Although mines can benefit enormously from a least-distance method of analysis, many other environmental projects stand to gain from it as well. Earthwork moving, reclamation, regrading, and balancing are not unique to the mining industry and occur in many sites around the globe.
Examples of other scenarios that could benefit from the least-distance method include, but are not limited to:
- Tailings Storage Facilities
- Breakwaters and beach rehabilitation
- Clearing and rehabilitation
- Large construction and civil projects
- Road and major building works
- Tunneling projects
In summary
Any business that incurs the massive costs of moving earth should consider carrying out a thorough investigation in the planning stages of their project.
Using the methods discussed above, which can be accurately produced using today’s software and tailored algorithms, companies can make better, more informed decisions. Ultimately, these decisions will help save substantial sums of money for organizations involved in projects requiring bulk earthwork.
