Dear Madalin Neagu, In ...
Published by Adeniyi Adebiyi, WASH Specialist/ Water Engineer at MSF Holland and Debaf Civil Geoenvironmental Consult
Dear Madalin Neagu,
In response to your questions about the use of DTH (down the hole hammer) while drilling; DTH does not start to work in non-cohesive and cohesive formation but starts working as soon as you enter the hard rock.
Since you are going to drill through non-cohesive to cohesive to hard rock; I believe you are going to go deeper. So, to execute this drilling successfully, you will need a drilling bits size of possibly 4.250 and 4.125 for 5 inches casing and 4.500, 4.625, 4.750 and 4.758 for 5.5 inches casing and 4.875, 5.125 and 5.375 for 6 inches casing.
Cheers