The Journal of Explosives Engineering - November/December 2024 - 27

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By Nathan Rouse, PE, PhD
Underground Perimeter Control Basics
Introduction to Underground
Perimeter Control
This is the first article on a series on underground perimeter
control. The concepts still apply to those of you in surface mining
that are interested in highwall control and crest protection.
Underground perimeter control is a general term that applies
to any blasting method that is used to reduce overbreak,
backbreak, and dilution. These common issues with underground
mines cause downstream cost impacts to mucking,
trucking, bolting and meshing, ventilation, and other parts of
the mine cycle. Let's go over some definitions before talking
about blasting methods to prevent these issues.
Definitions
Backbreak is crack damage outside of the final perimeter
of the blast. The cracks can be jointing or other geologic factors
that are opened by the blast energy (shock or gas pressure)
during detonation. They can also be fractures initiated by
the blast. Backbreak can create scenarios that lead to ground
fall and loose roof throughout the mine life.
Overbreak is the material that is blasted out past the design
perimeter or profile of a heading or stope. Overbreak is
extra material that must be mucked and trucked out of the
mine or tunnel. The overbreak material can be oversize and
non-ore material (dilution), which leads to further downstream
issues. Overbreak results in unnecessary downstream
costs for an operation from increased ground control (bolting,
meshing, shotcreting), to increased loading and hauling and
processing.
Dilution is low-grade or non-ore material that reduces the
value of the ore that is mucked out. Unplanned dilution can
occur from overbreaking into in-situ material or backfilled material.
For example, if you're mining along a hanging wall or
footwall and overbreak into the hanging wall or footwall, the
non-ore host rock material that falls into the muckpile will dilute
the ore beyond the dilution that was expected.
All of these common issues are typically due to three factors:
geology, drilling, and blasting.
24
Figure 1. Plan view of stope showing the components of dilution (Anderson
and Grebenc, 1995, figure 2.2).
Figure 2.
The Journal of Explosives Engineering
November/December 2024

The Journal of Explosives Engineering - November/December 2024

Table of Contents for the Digital Edition of The Journal of Explosives Engineering - November/December 2024

The Journal of Explosives Engineering - November/December 2024 - 1
The Journal of Explosives Engineering - November/December 2024 - 2
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The Journal of Explosives Engineering - November/December 2024 - 4
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