Forest Road Engineering Guidebook - Ministry of Forests

• detonation method
• delay pattern
• measures for flyrock control.
Flyrock, or excessive throw, can originate at different points in a blast. It can
come from:
• the forward movement or throw of the entire round
• the borehole charge breaking through the burden
• gas pressure forcing fragments into the air from within or around the collar
of the borehole.
The degree or threshold of rock movement that constitutes flyrock varies
depending on the blasting application. The Forest Road Regulation defines
flyrock as “airborne rock displaced beyond the road prism by blasting.”
Thus, the goal of blasting operations on forest roads is to minimize the
amount of rock that is cast beyond the road prism.
It may be difficult to eliminate all flyrock from every blast because rock conditions
and excavation requirements vary and can change frequently along
the road location. Nevertheless, blasting crews and supervisors should be
able to demonstrate that the practices they adopted were appropriate for the
observed conditions, and that their practices were altered in subsequent blasts
in response to changing rock conditions.
Causes of flyrock
Forest Road Engineering Guidebook
Flyrock can be caused by:
• excessive amount of explosive
• inadequate burden
• faults and cracks in the rock
• inadvertent loading of explosives into voids or fissures in the rock
• spacing and burden that exceeds the depth of borehole
• inadequate type or amount of stemming
• over-confined shots
• inappropriate drilling and loading patterns
• poor selection of delay sequences.
Measures to minimize flyrock include:
• precisely orienting and drilling boreholes to maintain desired burden and
spacing
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