It can be part of the construction process as well as part of the investigation process conducted on site before the structure is built. This process is performed under the supervision of a geotechnical engineer who remains present to make sure that the drilling meets the needs of the project.
One common reason for geotechnical drilling is site investigation. Site investigation is conducted to determine whether or not a site will be suitable for construction. It includes drilling to remove rock and soil samples, along with drilling to evaluate soil stability and other topics of interest. In the case of an oil rig, the drilling can also include investigation to find out more about the quality of the oil and where it is located.