When direct methods fail or are unable to be used, boring is used to explore soil at deeper depths. Depending on the method of boring, as there a several, they can provide both disturbed and undisturbed samples. When deciding which type of boring method is right for a particular task, there should be consideration to the ground materials, ground water conditions, changes in the soil and the possible disturbance to the materials. The 6 types of boring methods are:
- Auger Boring
Also known as thrust boring, auger boring is a cost efficient and fast method. It uses simple, flexible, light instruments that are inexpensive to bore both small and large holes. This method is best used on softer soils and stiff soils.
- Wash Boring
This method is popular as there is limited equipment needed, so it is portable and inexpensive.
- Rotary Drilling
Rotary drilling is best used with resistant strata, and to find out the rock quality from cracks and joints, as well as sands and silts.
- Displacement Boring
This method uses a mixture of boring and sampling. Piston types, slit cups or closed bottom samplers are used to force into the ground to the desired depth.
- Percussion Drilling
When auger boring or wash boring cannot be used, such as with soft rock or hard soils, percussion drilling is best used. This method can be used on any material but is not always economical.
- Continuous Sampling
This boring method takes continuous samples and is used to prevent the soils caving in.