Drilling Methods & Applications 

Direct push sampling utilises a percussive top drive hammer to drive a dual tube sampling system into unconsolidated formations. The sample is undisturbed and collected in a clear 1.2m long PVC liner. Samples can be opened on location for direct qualitative observation, transfered to a secondary storage medium, or retained in the liner for later removal.

Depending on the formation, this method of sampling is effective to a depth of 15m. Advantages include rapid speed, retention of sample integrity, reduced cost of managing and removing drilling spoil, and easy, accurate bore lithology profiling.

In addition, small diameter ‘pre-packed’ wells can be installed through the direct push system, or hollow augers in formations that are likely to collapse or when attempts are being made to reduce drilling waste. These wells have a PVC screen surrounded by a stainless steel mesh which is filled with graded sand and then sealed.

Pre-packed wells have a maximum ID of 37mm although it ensures an effective gravel pack in conditions that would otherwise compromise traditional installation methods.

Solid Auger Drilling 

Solid augers are effective in drilling soft to medium formations such as clays and weathered sedimentary rocks.

Solid augering often follows direct push sampling to increase bore diameter and allow the installation of conventional PVC monitoring wells. It is a fast and efficient method of drilling small diameter bores without introducing any drilling fluids.

Although effective to depths of 40m, solid augering is not effective in formations that are prone to collapse as there is no means of keeping the bore open for well installation.

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Hollow Auger Drilling 

Hollow augers are used when formations are prone to collapse. The hollow stem auger system has a continually open axial stem which allows a borehole to be simultaneously drilled and cased without the use of drilling fluids. Drilling the bore ‘dry’ ensures no contamination of the ground and air in the vicinity of the borehole.

The hollow stem allows for construction of the well prior to removing the augers. Bore walls are continually supported by the auger stem during the installation ensuring placement of an effective gravel pack around the screened interval.

Hollow augers are effective to depths of 30m with Numac’s Geoprobe machines.

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Hollow Auger Split Spoon Sampling 

The hollow auger drilling system can additionally be utilised to recover ‘split spoon’ soil samples with the use of a wire-line system similar to diamond drilling. Although this technique is slower and creates more spoil than direct push sampling, it is useful in formations such as sand where push tube sampling often meets with shallow refusal. Once the sample is removed the spoon is decontaminated ready for the next sample.

Rotary Air Hammer 

A rotary down-hole hammer is used in conjunction with a high volume, high pressure air compressor for drilling in hard formations, usually rock. Down hole hammers can be used to drill bores from 80mm – 200mm in diameter.

A down-hole hammer, like those shown here, is attached to the end of the drill string. Air filtering systems are installed on all our compressors ensuring the injected air is not introducing any contaminants into the borehole. In sensitive areas, suppression units can be supplied to reduce airborne ground up rock dust coming back up out of the bore.

The main limitation on depths drilled with air rotary methods is the size of the compressor being used. Attempting to drill through water bearing zones will dramatically increase the pressure and volume of air required to clear the drill cuttings off the bottom of the hole and lift to lift them out of the bore.

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Diamond Coring 

Our Boart Longyear DB520 machines can wire-line triple tube core to the following diameters and depths:

NQ3 - 210 m
HQ3 - 150 m
PQ3 - 100 m

The DB520s are set up for difficult access geotechnical drilling, supported by water trucks and compressors. Our rigs are capable of running a continuous casing in unstable formations to allow for accurate geotechnical sampling in all conditions, or well installation in difficult conditions such as landfills.

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Direct Injection (Remediation Products) 

The direct push technology used on our Geoprobe machines can be utilised as an injection methodology for remediation products such as Oxygen Release Compounds. Using specialised mixing equipment and powerful pumps, large quantities of in situ remediation materials can be injected at varying pressures and depths without creating any drilling spoil. ‘Spears’ with specially designed pressure injection points are pushed or hammered into the ground and attached to pumping equipment which premixes the slurry then pushes the mixture down to the spear point.

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Straddle Hydraulic (Packer) Testing 

Straddle hydraulic test equipment is designed for testing specific zones of cored holes once drilling to total depth is complete. When a zone of interest is identified in the retrieved core sample, the drill rods are moved back a suitable distance such that the deployed packer equipment can be inflated. In this configuration, two packers straddle the zone of interest, and, once inflated, two distinct functions are possible. The first is testing of water injection flow rates at various injection pressures. Injection pressures can be controlled via a bypass system on the injection flow meter board. The second is measuring water production rates from the isolated zone, with water samples of that zone only being collected for analysis.

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Standard Penetration Test (SPT) 

The standard penetration test (SPT) is an in situ dynamic penetration test designed to provide information on the geotechnical engineering properties of soil. The test uses a thick-walled sample tube, driven into the ground at the bottom of a borehole by blows from a slide hammer with a weight of 63.5kg (140lb) falling through a distance of 760mm (30in). The sample tube is driven 150mm into the ground and then the number of blows needed for the tube to penetrate each 150mm (6in) up to a depth of 450mm (18in) is recorded. Both the Geoprobe 7720DT and the DB520 machines are fitted with automatic SPT hammers.

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Concrete Core Cutting 

For environmental drilling operations on sites with cement slabs, concrete coring equipment is available to all crews. Coring the concrete slab allows for hand augering of the first 1-2m ensuring safe clearance of services.

Cores can be drilled from 50mm up to 300mm depending on the purpose of the bore location. Numac has additional attachments allowing concrete coring with the rig when conditions are not suitable for the stand alone units.

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Decontamination 

All rigs come equipped with high pressure washers for the decontamination of down-hole equipment between drilling locations and of the rig prior to leaving site. Water is carried on all support vehicles so there is no need to provide access to water on site.

Well Decommissioning 

Once a monitoring well has reached the end of its useful life it must be decommissioned. An application must be lodged to the relevant water authority to gain approval to decommission a well. The process of decommissioning wells can vary depending on its installation. In most cases environmental monitoring wells are filled with a cement/bentonite mix. This grout slurry is pumped into the bottom of the well up to the surface. The density of the slurry displaces any water currently in the well and ensures the entire column is filled solely with the mix.

In some circumstances it may be necessary to ‘pressure grout’ the well. In this instance the grout slurry is pumped under pressure into the well forcing a predetermined amount of the mix out through the screen and into the annular space. This is not required in normal circumstances though can be completed as an extra safeguard where there is a risk of cross contamination.

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Non-Destructive Drilling 

In efforts to eliminate manual handling risks and risks associated with hitting underground services, we have commissioned non-destructive clearance units as part of our pre-drilling protocol.

The units use high pressure water to break up the fill material and a powerful vacuum to remove it from the bore ensuring good clearance from subsurface infrastructure prior to commencing drilling. Samples can still be taken via hand auger at the required depths in consultation with the operator.

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