The first operation of the drilling activity after erecting the drilling equipment and all the connections are ready for work is to place the stand or drive pipe, which together with the drive-shoe, the casing or lining tube, drill rods, core-shell, core-lifter and drilling-bit. This consists of a length or lengths of especially prepared pipe, or in shallow depths or ordinary pipe, generally 48 mm to 123 mm in diameter. Its purpose is to take the returning water and cuttings from the bottom of the drill hole, and deliver them into core boxes on the drill-room for inspection, so that the nature of the rock may be seen by the geologist, gold prospector or metallurgist. Also, the pipes are used to prevent the loss of water which would be inevitable in the fissure rocks or alluvium forming the immediate surface of the ground.
In choosing a site for drilling, it is better to select a spot where there is at least thickness of top soil. In cases where the rock lies at a maximum depth of three meters it is better to sink a hole to the solid rock and place the stand pipe in a niche cut therein; at a spot previously marked as directly in a vertical line from the center of the drill core. It is necessary to augur a hole with the tolls specially provided for this purpose as deep as practicable, large enough to take the stand-pipe and to force it through by striking it heavily at the upper end. When this is resorted, the stand-pipe is fitted with a driving head.
When it is necessary to drill holes in alluvium zones that consists of clayey material, it is generally found that the rock can be reached without complication, but should it be found that owing to caving, the hole for the reception of the stand-pipe can only be drilled partially into the drift, then to reach the rock from the deepest depth drilled. If much drift is anticipated, it is better to start with a large pipe, driving it as far as possible and finishing with one or two smaller. Where several sizes are used, each is subjected to only part of the friction of the loose material in pulling it out, and hence more easily drawn. The smallest size must be sufficiently to admit casing.
The stand-pipe must now be forced through the rock bottom. To do this, the pipe is fitted with the drive-head. As the engine runs, the cable end is alternately loosened and pulled, the result is that the pipe is raised to a suitable height and when the cable is loosened immediately drops and strikes the drive head. Water is forced for the purpose of stirring up the loose material and carrying it to the surface in the space between the wash and stand pipes. Pieces of rock, clay, gravel, and others can be brought to the surface by these means. If large fragments are encountered, they must be broken down.
Drilling Equipment