Determining the optimal number of pushbacks is key to balancing workload, costs, and profitability in mining operations. While fewer pushbacks simplify scheduling, they may lead to significant overburden, whereas more pushbacks offer better NPV but increase complexity. Learn how to find the right balance based on deposit size, equipment, and operational goals.
Video transcription
How pushback quantity affects NPV
Analysis of scenarios from three to seven pushbacks reveals a clear economic pattern. Fewer pushbacks create large overburden spikes early in development—with three pushbacks, ore targets are met only from the fourth planning interval, significantly reducing net present value. As pushback count increases to five or six, overburden volumes become more manageable and NPV improves progressively. Seven pushbacks show the highest NPV with stable stripping volumes, though design complexity may limit practical feasibility.
Finding the optimal number of pushbacks
Six pushbacks emerged as the sweet spot for the analyzed deposit conditions, balancing economic returns against design complexity. Adding a seventh pushback doesn't significantly improve NPV but increases planning difficulty and potential execution risks. If six pushbacks prove impractical, five can work with extra focus on early development stages. Each deposit requires individual analysis since the optimal number depends on specific geological and operational conditions.
Tradeoffs of smaller versus larger pushbacks
Smaller pushbacks get worked through faster, leading to more frequent excavator relocations that reduce productivity. More pushbacks mean more haul roads, increasing construction costs and development time. Narrow pushbacks also carry higher risk of unexpected stability issues or geological surprises disrupting operations. On the positive side, more pushbacks are easier to plan and execute, allow working multiple phases simultaneously when needed, and deliver better economic outcomes through reduced early stripping requirements.
Guidelines for pushback sizing
Pushback width should equal two to five working area widths of the primary mining equipment, with three to four being the recommended range for most open pit operations. Each pushback should start at pit surface and extend to maximum depth with the bottom targeting the ore zone. Every pushback must connect to and extend from the previous one—the exception being uneven deposits where stripping one section may be more efficient. The fundamental scheduling principle is starting each pushback as late as possible while reaching minerals as quickly as possible.