Depending on the type and character of the surface, different drilling methods are adopted. Here’s a quick overview of popular drilling methods.
Direct Push Soil Sampling
This is perhaps the simplest of all the drilling methods. A percussive top drive hammer is used for driving in a dual tube type sampling system inside the unconsolidated formations. Depending on the formation type, this drilling and sampling method is effective up to a depth of 15m. Rapid speed, sampling integrity retention,accurate profiling of bore lithology and reduced cost are some of the major advantages offered by direct push sampling.
Solid Auger Drilling
For drilling soft and medium formations like clay or weathered sedimentary rocks, solid augers are extremely effective. Solid auger drilling is used following the direct push soil sampling for increasing the bore diameter.It is also used for allowing the conventional PVC monitor wells to be installed. Solid augering can be effective up to a depth of 40m. It is an efficient method for bores with small diameters,without using any kind of drilling fluid. But solid auger drilling offers no means of keeping the bore open for well installation. It is not an effective drilling method for formations that are prone to collapsing.
Hollow Auger Drilling
If the formation to be drilled is collapse prone, then hollow augers are used in place of solid auger drilling. These hollow stem systems come with a continually open axial stemfor drilling and casing the bore hole simultaneously, without using drilling fluids. Hollow auger drilling is effective up to a depth of 30m.
Hollow Auger Spoon Sampling
For recovering split spoon soil samples, a wire-line system akin to diamond drilling, can be additionally utilized.Hollow auger spoon sampling is a far slower technique than direct push sampling.It also generates more spoil. Yet, it is a highly useful drilling method for formations, like sand; where shallow refusal is a regular problem for push tube sampling.
Rotary Air Hammer
When it comes to drilling in hard formations, like rock, rotary air hammer along with a high pressure and high volume air compressor is used. These are also called down-hole hammers and are used for drilling bores with diameters of 80mm to 200mm. A rotary air hammer is normally attached with the end of a drill string.It also comes with installed air filter systems to ensure that no contamination is introduced by the injected air inside the bore holes. It can also be supplied with a suppression unit for reducing the airborne rock dust coming out of the bore.
The size of the compressor is usually the limitation of rotary air hammer drilling systems. Drilling through zones bearing water requires a tremendous increase in the pressure and volume of the air needed to clear the drill cuttings from the bottom of the hole, and also for lifting them out of it.
This is the best drilling system for difficult geo-technical drilling. It is supported by compressors and water trucks. For the most accurate geo-technical sampling in different areas, these rigs can run continuous casing.This is true even inside unstable formations and difficult conditions, like landfills where well installation is a truly difficult proposition.
Geoprobe machines use the direct push technology. They can be used as an injection method for remediation formations like oxygen releasing compounds. Powerful pumps and special equipment for mixing are used for injecting large quantity of situ remediation materials at different depths.This is accomplished without generating any spoil during the drilling process. “Spears”containing pressure injection points are first hammered or pushed into the ground.Then they are attached to the pumping equipment for pushing the mixture down the pressure points.
Concrete Core Cutting
Concrete core cutting is used for environmental drilling at sites with concrete covering or cement slabs. In concrete core cutting, hand augering is used for the first couple of millimeters to ensure safe clearance of the service. With concrete core cutting, depending upon the purpose and the bore location, the core can be drilled from a depth of 50mm to 300mm.
Standard Penetration Test
Standard penetration test (SPT) is a situ dynamic penetration test.It is designed for providing geotechnical engineering property information of the soil. With a slide hammer weighing 140lb falling through a distance of 30in,thick walled sampling tubes are driven to the bottom of the borehole.Then the number of blows required to penetrate 6 inches into each tube is recorded.
Non-destructive drilling units are used for eliminating the risk of manual handling.They are also used to minimize the risk of hitting underground surfaces while drilling. As a part of the pre-drilling protocol, non-destructive drilling units use water with high pressure for breaking up the fill material.Then a very powerful vacuum is employed to remove them from the bore hole, ensuring good clearance. With non-destructive drilling, samples can still be collected by hand augering during any stage of the drilling process.