D 88.9 – D 152.4 with hydraulic drifter
The name “Overburden Drilling” results from the composition of the earth crust. The bedrock is covered with loose layers of earth consisting of sand, gravel, boulders combined with loose ground and other deposits. All these formations are grouped together under the umbrella term “Overburden”, which overlies the bedrock.
Certain drilling processes make it necessary to support the wall with tubes. The system shown here is powered by a hydraulic hammer, which turns and strikes the whole drill string from above, consisting of an outer and inner rod. Air or water is flushed down the center of the inner drill string to the end of the drill hole. It discharges the cuttings in the annuls between both rods through the flushing holes above. This drilling system is used for relatively shallow depths.