Description: Percussion (also known as cable tool) drilling refers to the alternate breaking of the formation and cleaning the hole. Percussion drilling is often undertaken with different tools – eg a chisel to break followed by a bailer to remove the spoil. There are also clay-cutting tools available that can both cut and remove the spoil. The drilling tools and weights (referred to as the tool string) is suspended from a rope or steel cable and reciprocated through a stroke of 1 to 3m. Small amounts of water are usually added to the hole to help loosen the formation. It is often necessary to line the hole with temporary steel casing to prevent collapse.
Capability: In principle, percussion drilling can deal with most ground conditions but progress can be very slow in hard rock. Due to the limited energy inputs of hand percussion, progress is considerably slower than for conventional (mechanised) percussion drilling. If temporary casing is used, considerable time and suitable tools are needed to drive it into the ground and remove it. Depths of 20 to 30m are possible if there is no temporary casing required, otherwise the limit is about 15m.
Locations: Zimbabwe, Tanzania, Liberia, Niger, Nigeria, Chad, Ghana, Central America.
Availability: Hand percussion is not commonly used today. However, there are some cases of mechanised percussion, and the principles of percussion are used alongside other techniques such as sludging, or have been integrated into other combination hand drilling techniques such as rota-sludge and pounder drilling.
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