Clay cutter drilling in Glacial Till

CONSALLEN

The CLAY CUTTER

The
CLAY CUTTER
The clay cutter employs the weight of a sinker bar in free-fall to drive it into the material being drilled. This is not only clay, but most other materials including sand & gravel and chalk (soft limestone). Material is recovered each time the drill string is hoisted out and progress can be very rapid. The same tool can also be driven using a sliding hammer under water or when the free-falling tool does not pick up the plug it has cut, due to friction or suction. There are variations on the geometry of this useful device, with high short windows and removable doors, for some materials.

The picture shows the way a firm to stiff clay - including fist sized boulders - can be drilled quite easily, generating 125mm (5-inch) diameter plugs of clay up to 300mm (12") long in this case. These are discharged from the cutter by a push-out tool when the helper presents the clay cutter, and the drill string is hoisted. Material falls into the bin for disposal. This hole was advancing at the rate of 4 metres (13 ft.) per hour - with no mess. The video on the main page gives a better indication of the usefulness of this tool.

RETAINERS

The clay cutter shown has a screw-on shoe, allowing various lifting devices to be placed between it and the tool body. An extrusion ring may be useful in softer clays, allowing the plug to be easily pushed out of the clay cutter window. A clack valve can be used in sands below water where a bailer would remove too much water and cause the hole to collapse. The core retention basket shown right is very useful, and will retain an undisturbed sample for examination at ground level. Other retaining devices can be used, including a 'Valvate disc', which is a flat version of the basket catcher, made of rubber - see below.

The middle picture shows a clack valve from a bailer, which is also very useful in a claycutter in certain materials. As illustrated below, it can be very effectve for drilling gravel below water. Dry gravels and sands can be induced to behave in the same way by adding some water to the hole.

Valvate discs (lower picture) can be used in sands and gravels in the same way as basket catchers and clack valves, but are superior in some materials. They have the advantage that they can be stacked, and claycutters can be cleared using a suitable post upon which the claycutter can be landed, bushing the material up and out of the windows.

The clay cutter is a very versatile tool; is the 'auger' in shell & auger drilling, where it is the main drilling tool.

Click the images for a larger view.

Plastic catcher used to retain granular materials - particularly in water

GRAVEL DRILLING

The clay cutter shown here is being used to drill gravel below water. A clack valve was being used to lift the gravel very effectively by surging the tool ahead of the casing.

The gravel is up to about 20mm size, is free draining, and the water has passed through the clack as the tool is lifted from the borehole. Because little water is removed, static pressure is maintained in the material being drilled, and with no flow into the hole, to wash out fines, collapse does not occur. Casing may sink under it's own weight in such conditions.

The 140mm od clay cutter shown will lift gravel and cobbles up to about 100mm (4 inches) diameter with a basket catcher. Bigger cobbles can often be recovered after jambing in the cutting shoe. Many rotary systems experience great difficulty with bigger gravel and cobbles, often finding them impossible to drill.

Clay cutters can be suplied fitted with side doors, resulting in greater quantities of granular material being removed for each operation of the tool. A similar effect is achieved using a specialist gravelling type tool, with high, short windows.

Note:
Gravel is defined as being from 2 to 64mm size, and cobbles are from 64 to 265mm.

DRILLING SAND

A clay cutter with a basket catcher fitted, and drilling a marine soft silty clayey sand, some of which has fallen out as the tool was pulled above the temporary casing. While a bailer could have been tried at this site, it would probably have been more difficult to empty than the clay cutter - and slower drilling as a result.

In hard dry sand, adding water enables a clay cutter to be surged and filled, advancing the hole very quickly.

Consallen Group Sales Ltd., P.O. Box 2993, Sudbury, Suffolk CO10 0ZB, UK.
Tel/Fax: +44-(0)1787-247770; e-mail: sales@consallen.com