Pushback Generation Essentials

Lexicon of terms

Pushback (also called "stage", "phase" and "cutback"): a pit that is big enough to be mined bench by bench with available mining equipment. Normally, a pushback is expected to have the following properties:

Blocks in a pushback are spatially connected (contiguous); unlike LG phase pushback they cannot be a collection of disjointed sub-pits.
Pushback location within ultimate pit limits avoids leaving behind unmineable “remnants”.
Pushback locations relative to one another guarantee continuous access to all active pits, which can be achieved by requiring that pushback boundaries be separated by a minimum distance, except when these boundaries coincide with the ultimate pit limits.
Pushback boundaries are smooth enough to be practical.
Pushback size, usually defined by ore tonnage, has to be big enough for bench by bench mining; it should not be much bigger than that to avoid NPV losses and ensure enough flexibility for scheduling.

Pushback Generator OES: Pit by Pit OES with respect to pushbacks.
Pushback Adjustment: a digitized or imported outline affecting location and shape of a pushback.
PB Local Include: pushback adjustment forcing all blocks within the outline and within the ultimate pit limits to be included in the pushback.
PB Local Elevation Limit: pushback adjustment restricting the pushback depth for the blocks within the outline.
PB Include: pushback adjustment restricting the pushback to be contained within the outline; the pushback cannot extend below the limiting bench.
PB Exclude: pushback adjustment allowing no blocks within the outline to be included in the pushback.
PB Forced Limit: pushback adjustment forcing all blocks within the outline to be included in the pushback; the pushback cannot extend below the limiting bench. The boundary size will overwrite the control variable value.

Find out more about limiting boundaries...

How it works

Pushback Generator reevaluates Pit Optimizer OES. It combines the blocks into spatially connected sets and adjusts these sets to meet the requirements of pushback definition. Whenever possible pushback limits are set close to an LG phase limits. Once all the pushbacks are defined, Pushback Generator creates Pushback Generator OES.

Note that in most cases, the last “pushback” contains just blocks left over in the ultimate pit and may not satisfy the usual pushback requirements.

Pushback slopes

Pushback Generator utilizes Pit Optimizer slope definitions. If you wish to generate pushbacks with slopes that are different, for example steeper than those of the ultimate pit:

Define new slopes in Pit Optimization Settings (Optimization control bar | Ultimate Pit | Settings); you can use different slope regions and different slope angles.
Using the Ultimate Pit tab, select Use pit selected from the list below and choose an ultimate pit file (Studio NPVS-generated ultimate pits are saved as “Optimized Pits” files)
Run the Pit Optimizer to obtain new Pit Optimizer OES.
Run the Pushback Generator.

Time flow and NPV calculations

Pushback Generator calculates time and NPV for the Pushback Generator OES in exactly same way as Pit Optimizer does it for its OES. Typically, Pushback Generator NPV will be less than Pit Optimizer NPV because demands of practical mining by pushback place new constraints on NPV maximization.

Pushbacks and blending

Unlike blended nested pits obtained from Pit Optimizer blended OES, pushbacks are not blended. Trying to get blended pushbacks is hopeless because blending requirements are rarely consistent with the requirement of spatial connectedness of pushback blocks. Unless you must mine pushbacks one at a time, this is not a problem that cannot be rectified by the Scheduler.

Some mines, for example industrial minerals operations using small shovels and trucks, may not need pushbacks. In this case, the alternative is to mine blended nested pits directly.

Adjusting pushbacks with digitized outlines

Pushback adjustments allow you to customize a pushback sequence beyond what is possible with settings controls; you can change the shapes of individual pushbacks and create alternative mine development scenarios.

Each pushback can have its own set of adjustments. An adjustment set must always have one Global Limit outline and any number of other types of outlines. The outlines are digitized in Plot View or imported and assigned to particular pushbacks in Size Control dialog of the pushback settings.

A common scenario:

Run Pushback Generator without adjustments.
Create an adjustment object by digitizing outlines for the first pushback, enter the object name in the Size Control dialog and Run the Pushback Generator again.
Repeat step 2 for some or all remaining pushbacks.

	Related Topics
	Quick Start Import Essentials Economic Model Essentials Pit Optimization Essentials Scheduler Essentials MAO Essentials MFO Essentials

JMN 20065_01_EN