Using the mud rotary method, the bore hole is advanced in rock and overburden by rapid rotation of a drill bit mounted at the end of drill rods.
The bit breaks material at the bottom of the hole into small pieces. These cuttings are removed by pumping drilling fluid (water, or water mixed with bentonite or fluid enhancers) down through the drill rods and bit and up the annulus between the bore hole and the drill rods. The fluid cools the bit, stabilizes the bore-hole walls and prevents fluids flowing between the hole and surrounding earth materials, reducing cross-contamination between aquifers.
Drilling fluid circulates in the bore-hole as it pumps down through the rod string, where it picks up drill cuttings and carries them to the surface.
In bedrock or solid rock , wire-line rock coring collects bedrock cores for engineering and geological study.
A diamond bit attached to a core barrel is lowered into the hole, and core rods of the same size are attached to reach the bedrock starting point. Rock core samples are obtained by removing the inner barrel assembly from the core barrel of the drill rod using an overshot retriever attached to a drill rig winch.
Typical uses include foundation investigations, material sources, rock cut investigations and general rock coring of native bedrock substrates to obtain geotechnical data and samples.