Overburden Drilling Systems D 114.3 - D 177.8 with double head drilling unit (rotary/rotary-percussion)
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 soil 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 has two heads which can be moved opposite to one another, rotary (outer rods) and rotary-percussion (inner rod). The rods are counter-rotating independently. Air or water can be flushed down the centre of the inner drill string to the end of the drill hole. It discharges the cuttings in the annulus between both rods through the flushing holes above. The slide of the rotary drives allows the inner rod to move up and down relative to the outer casing. The pilot effect of the inner rod gives better alignment. So, these systems are especially suitable for horizontal drilling, e.g. injection drilling for tunnelling and exploratory drilling.
Examples of application: