Hole Deviation (msHD, msID)
Definition - What does Hole Deviation (msHD, msID) mean?
Hole deviation is the unintentional departure of a bore from its ideal trajectory in the bore's design pathway. The bore may be off a few degrees at its start for a variety of reasons but as the bore progresses, and if that initial error isn't corrected, the bore may diverge from the design pathway altogether. This can result in both physical and legal problems.
Trenchlesspedia explains Hole Deviation (msHD, msID)
The principal causes of hole deviation include setup error, drill platform instability and drill rod inefficiency at the beginning of the bore. Other causes include the type of substrate through which the bore passes and the condition of the drill and bit.
A two-degree error at the beginning of a bore causes 3.5 meters of error at 100 meters. When added to any incurred deviation further along the bore, expensive remedies may be required to save the bore.
Rock composition through which the bore passes will influence, or can cause, hole deviation. Layered strata or rocks with high fissility cause deviation in a bore as it passes through the layering or fissility at an angle.
Worn drill rod elements, sloppy barrels and poor bit design or condition also contributes to crooked holes.