Sonic rigs are ideal for use in environmental investigations as they have the ability to:
- drill straight holes
- install continuous, multi-chamber well tubing
- drill and core through landfill debris
- drill angled holes
- drill without using drilling mud
- drill any broken or saturated soils or alluvium material
- perform many other types of environmental, drilling-related operations with exceptional core recovery.
These core samples are extruded into clear plastic sleeves, which minimises the loss of volatile organic compounds and reduces the risk of operator exposure to in-ground contaminants. The clear plastic sleeves also allow field screening devices to provide immediate soil chemistry information. Core samples can then be subjected to a detailed visual examination and analysis, followed by photographing, sampling and archiving for a permanent record of existing soil conditions. This allows the creation of an accurate description of the stratigraphy and lithology of the underlying geological setting.
How the sonic drill works
The sonic drill is outstanding in its ability to provide continuous, highly representative and relatively undisturbed core samples through any geological formation, including boulders and bedrock. Coring, in overburden material, is performed as a mostly dry process, producing core samples that range from 3-8˝ in diameter. All core samples are large enough to provide duplicate samples.
The sonic head is based upon the principle of high-frequency vibration. The hydraulic motors on the exterior of the head oscillate offset internal weights at speeds reaching 5000rpm. As a result of the weights being offset, it creates a vibration in excess of 140hz.
An example of our neatly packaged and labelled sample boxes • SPT sample casing and sonic tools
A hollow, cylindrical, diamond-encrusted drill bit rotates at high speed, cutting through the ore and extracting a solid sample that travels up through the drill pipe. This gives an unbiased estimate of the deposit as no other particles have a chance to contaminate the ore on its journey up the drill hole.
Diamond core drilling (exploration diamond drilling) utilises an annular diamond-impregnated drill bit attached to the end of hollow drill rods, to cut a cylindrical core of solid rock. Holes within the bit allow water to be delivered to the cutting face, which provides three essential functions: cooling, lubrication and removal of drill cuttings from the hole.
The advantages of this are:
- a truly representative in-situ sample
- the availability of multiple sizes
- the ability to apply accurate directional techniques to hit specific targets
- the production of a clean bore hole for geophysical logging
- the ability to achieve superior depths
- the ability to assess geological orientation.
This system is used in consolidated soils and rock where sonic drilling starts to slow down and become a less economic option.
Air core drilling and related methods use hardened steel or tungsten blades to bore a hole into unconsolidated ground. The drill bit has three blades arranged around the bit head, which cut the unconsolidated ground. The rods are hollow with an inner tube sitting inside the hollow, outer rod barrel. The drill cuttings are removed by injection of compressed air into the hole via the annular area between the inner tube and the drill rod. The cuttings are then blown back up the inner tube to the surface where they pass through the sample separating system to be collected if needed. Drilling continues with the addition of rods to the top of the drill string. Air core drilling can occasionally produce small chunks of cored rock.
This method of drilling is used to drill the weathered regolith, as the drill rig and steel or tungsten blades cannot penetrate fresh rock.
In good conditions air core drilling can achieve depths approaching 300 metres. The cuttings are removed inside the rods and are less prone to contamination, in comparison with conventional drilling, where cuttings pass to the surface via outside return between the outside of the drill rod and the walls of the hole.
Reverse circulation (RC) drilling is similar to air core drilling in that the drill cuttings are returned to the surface inside the rods. The drilling mechanism, a pneumatic reciprocating piston known as a hammer, drives a tungsten-steel drill bit. RC drilling requires much larger rigs and machinery and routinely achieves depths of up to 500 metres.
RC drilling ideally produces dry rock chips, as large air compressors dry the rock out ahead of the advancing drill bit. This type of drilling is slower but achieves better penetration than air core drilling.