What Does Percussion Drilling Mean?
Percussion drilling is a drilling method in which a heavy hammering or cutting bit is attached to a cable and inserted into the borehole. The heavy bit or hammer is repeatedly lifted and dropped, thus boring through the earth.
The hammer is made of hardened steel with carbide on the chisel-shaped bit. Cable percussion boring is a common drilling method used for geotechnical site investigations. This drilling method allows the installation of casing inside the borehole allowing for deep boreholes. It is the most convenient and common method of intrusive geotechnical investigation.
Trenchlesspedia Explains Percussion Drilling
Percussion drilling can be used to dig boreholes up to 60 m depth depending on ground conditions and access to the site.
Different sample types can be retrieved using this method such as:
- Cohesive disturbed samples.
- Granular disturbed samples.
- Undisturbed samples.
- Piston samples.
- Split barrel samples (used standard penetration testing).
The cable percussion drilling rig consists of a winch and a derrick that can be folded down and towed to and from the site.
For cohesive soils, the borehole is drilled using a clay cutter, and for non-cohesive soils, a shell is used. The borehole sides are supported using casing as the borehole proceeds.
For very hard ground that is difficult to penetrate or for obstructions such as boulders, a chiseling tool can be used. Tests such as the standard penetration test (SPT), borehole vane test, and falling or rising head tests can be carried out within the borehole.