Drilling is an important and necessary part of soil sampling in order to provide information regarding the characteristics of the sub-soil structure. Boring machines come in two main types, large-diameter and small-diameter. Large diameter boring machines are rarely used due to expense and the need to leave the site as undisturbed as possible. Small-diameter boring machines are used to allow the Soil Tester to examine soil or rock fragments from the drilling operation, to retrieve soil samples at depth, and to perform in-place soil tests.
The most common type of drill used for sampling is the Continuous Flight Auger. This is a method of sampling using an auger as a corkscrew. The auger is screwed into the ground then lifted out. Soil is retained on the blades of the auger and kept for testing. There are other methods of sampling via the borehole. One is the use of a steel tube that is driven into the clay at the bottom of the bore hole and enables a solid sample to be withdrawn.
The drilling machines that we use are hydraulicly operated. We have two types: A machine that is mounted on the back of a Fuso 4WD truck. This is used were reasonable access is possible; A second type is a Boxer 320 Mini skid-steer. This has tracks and is transported to the site. It is used where access is difficult. For example, narrow access to the rear of an existing building, wet and muddy conditions or where low surface impact is needed.