Introduction

A study of the rocks exposed at the surface, their structures and the geology of the area gives sufficient information of the conditions that may be available below ground. More detailed information is, however, obtained by boring and interpretation of the data available from it. The term drilling is nowadays coming into use for boring.

In mining and allied branches of engineering drill holes may be drilled for the following purposes.

1.  To prove the existence of minerals, to get an idea of rock structures and to obtain knowledge of the rocks and the mineral beds, such as depth, nature, thickness and gradient.

2.  To get core of the rocks from which bearing pressure of the ground can be found out. This information is necessary for heavy winding engine foundations required for deep shafts.

3.  To know throw of the faults; this is conveniently done from underground workings.

4.  To drain off gas or water from old workings.

5.  To carry electric cables, signal wires, stowing pipes or water pipes to the underground from surface.

6.  To have tube wells for water supply to colonies.

7.  To blast rock/mineral in a mechanised quarry where holes of  9 to 18 m depth and 125 to 300 mm in dia. may be drilled.

8.  To render possible the injection of cement into the strata in a method of shaft sinking known as "cementation method of shaft sinking".

9.  For ventilation of underground mine workings.

An interesting application of bore holes drilled from the surface to seal off with incombustible material underground fire and thereby to quench it was witnessed at Kurasia collicrv (MP.) in 1961.

Sizes of drill holes drilled in mining areas usually vary from 25 mm to 125 mm though larger diameter holes may be required for carrying stowing pipes, water pipes, or for blasting in mechanised quarries. For deep holes, the size is larger at the start and is gradually reduced with depth.