Combination pilot drilling with HDD

After the pilot drilling with double wall rods a reamer drilling with a backreamer and simultaneous pulling in of the product pipes is carried out as shown in the figure. The bentonite, which serves to convey the soil excavated by the reamer drilling and at the same time as lubrication for the product pipe string, can either be pumped from the target shaft through the product pipe or through the centre of the inner pilot rods to the backreamer.