subdrilling

subdrilling

[¦səb′dril·iŋ]
(engineering)
Refers to the breaking of the base in which boreholes are drilled 1 foot (0.3 meter) or several feet below the level of the quarry floor.
References in periodicals archive ?
Less subdrilling is required because detonation pressure is higher.
With these methods, there are often significant deviations --such as the burden, spacing, bench height, subdrilling and hole azimuth and inclination--between the planned and actual geometric parameters of a blast This brings about a variation of the explosive energy, resulting in course fragmentation, inconsistent muck-pile uniformity and higher production costs.
Benches in Lumwana's 6-km-long pit are generally kept at 8 m in height to minimize ore dilution and allow single-pass drilling, but occasional circumstances require double-height benches; all are sunk with 1 m of subdrilling to ensure good toe breakage and pit floor evenness.
As a result, there are often significant deviations - such as the burden, spacing, bench height, subdrilling and hole azimuth and inclination - between the planned and actual geometric parameters of a blast.
Three mines sample subdrilling, and one mine takes two samples from each blasthole.