Drilling techniques

We carry out both hand drilling and mechanical drilling services. As a specialist in drilling and sampling, we can carry out all the usual drilling techniques. We have experience with drilling in almost all geological formations. On the basis of the problem, the geology and the location, we determine which technique to use.

ROTOSONIC DRILLING

In this advanced form of drilling, high-frequency resonance energy is generated in the Sonic drill head by two rotating weights and transmitted along the drill pipe to the bit. In roto-sonic drilling, the drill bit rotates at the same time, so that the resonance energy is evenly distributed between the bit and the material to be drilled. This allows us to drill almost all formations (from clay, gravel and sand to rock) with maximum productivity.

With sonic drilling, we take samples of high quality and mixed geology. An additional advantage is that little excess drilling material is released. We us the technique for both environmental and geotechnical research. As with other pressure- and impact drillings, we also use sonic drills to place sampling tubes.

PERCUSSION (BAILER) DRILLING

A bailer is a pipe with a cutting edge at the bottom and a horizontal valve just above it. Because the pipe moves up and down, the loose material collects in the bailer. The valve mechanism ensures that the drilled material does not fall back into the borehole when the bailer is raised. Because the pipes are drawn in a very controlled way, we are able to apply sampling tubes and seals very accurately. Since this drilling technique only works below the groundwater level, we pre-drill with an agave drill.

We can carry out bailer drilling to a depth of more than 50 metres with a maximum diameter of 324 mm. In our carefully conducted bailer drilling, the soil samples, although very disturbed, can still be used for profile tracing. In very heterogeneous soils the profile tracing is less reliable than in homogeneous soils. The strongly disturbed samples from the bailer are usually not suitable for sampling. However, with the aid of a coring apparatus, we can take an undisturbed sample at the desired depth after removal of the bailer.

DIRECT-PUSH AND HAMMER DRILLING

With this type of drilling, a (semi-)cylindrical drill with a cutting edge is pressed or hammered into the soil. Using an inner tube and a plastic tube, we take undisturbed samples at any depth and, if desired, continuously. Because we do this without working water, there is no question of washing or dilution and the samples are very representative for the soil layer.

We carry out direct-push and hammer drilling both manually (e.g. using a percussion coring tube equipment) and mechanically. The maximum depth that can be reached varies from 10 metres in case of manual drilling to more than 30 metres in case of mechanical drilling. The drill diameters vary from 32 mm to 86 mm.

Direct-push and hammer drilling techniques can also be used to install sampling tubes. These can be pushed directly into the ground and positioned with the help of the drill pipes. In the latter case, the drill pipe is closed off at the end with a removable or a ‘lost’ drive point which functions as a casing by which the filter can be installed at the correct depth. The advantages of this technique are a minimal soil disturbance and no excess soil material released during drilling.

CORE DRILLING

During core drilling, a rotating outer core barrel with drill bit, is drilled at depth together with a stationary inner core barrel. This is done with the addition of water, mud fluid or air to cool the drill bit and remove the bore dust. The drilling is done in equal steps of 1.5 metres (or a multiple thereof). After each so-called run, the inner core barrel is drawn out of the drill casing, emptied ans the core is stored in a special box. We mainly use core drilling to pass through soil layers that are too hard for other techniques (such as bailing) when drilling deeper.

AUGER DRILLING

We carry out auger drilling up to a diameter of 320 mm, using the large diameters when sampling soils with a lot of coarse material. Depending on the drilling rig, the base and the drilling diameter used, we reach depths of more than 50 metres. There are three types of auger drilling, each with a different application:

Continuous flight auger

The continuous flight auger consists of a spiral rotated by a drill engine. The rotating movement causes the drill to screw itself into the soil. The drill is repeatedly lengthened by using an extension piece until the desired depth is reached. Then we pull up the soil with the drill. With our well executed continuous flight auger the soil is barely disturbed. This technique is therefore suitable for taking soil samples for environmental and archaeological site investigations and for tracing profiles.

Hollow auger

The hollow auger is a spiral drill with a hollow inner pipe that is closed off at the bottom with a lockable lid, which can be raised using a cable. At the reached depth we take a sample with the help of a ram cutter or a cutting box. Optionally, we install a sampling tube through the hollow auger. Since the hollow auger actually works as an Archimedes screw and a large quantity of soil material is raised during drilling, this method is not suitable for tracing profiles.

Cased auger

Finally, Sialtech can carry out cased auger drilling, in which the continuous flight auger drills through a casing. The casing is lowered at the same time as the auger. This technique is used to drill through a contaminated soil stratum and when percussion drilling is not possible such as in the case of clay soils and soils above groundwater level.