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 has two rotary units that can rotate opposite to each other. The rods counter-rotate independently. Air or water is 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 ahead the outer rod and can even be pulled back. The pilot effect of the inner rod gives better alignment. So, these systems are especially suitable for horizontal drilling, e.g. injection drilling for tunneling and exploratory drilling.

Depending on the ground conditions, the drilling can be made either with rotary drill bits or DTH-hammers. Another possible way to discharge the cuttings is to use auger drill rods, especially, if flushing with air or water is not possible with this system to drill the whole drill string in together, the drilling is made separately. First the outer casing, followed by the inner string.

Product information sheet:
Overburden Drillings Systems with rotary head (371KB)
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Examples of application: