Definition from Trenchlesspedia

What Does Core Drilling Mean?

Core drilling is the process of drilling below the earth's surface to obtain a core of soil or rock sample in order to determine its properties. Core drilling is an important part of geotechnical site investigation that is carried out for the planning and construction of sub-surface structures such as tunnels and pipelines.

A core drill, which is cylindrical and hollow and made of metal with diamond or carbide coated drill tips is used for the purpose. The core drill cuts through the ground surface to extract the sample from the required depth. Core drilling retrieves usable samples for geotechnical investigation.

Core drilling can be accomplished using rotary drilling to obtain core samples from the bottom of the boreholes. A rotating core barrel fitted with an annular bit is used for this purpose. The core barrel retains the core, which is brought to the surface and recovered.

Another method is the directional core drilling method introduced by Devico technology, which is able to control borehole deviation and accurately steer the hole towards the target while collecting core samples. When the borehole reaches the area from where a sample is to be collected, a wireline core barrel is placed instead of the directional core barrel, allowing for a full-size core sample.

In case of a deviation, the directional core barrel is reinserted and the hole is steered to the desired direction. Directional core drilling can also provide continuous core sample and geological information from the planned tunnel trajectory, which is not possible with other core drilling techniques.