Geotechnical Site Investigation – Rotary Drilling Capabilities

As part of an ongoing process of developing our in-house contracting capability, the Southern Testing Field Operations team have recently expanded their rotary drilling capability to include high-quality rock core recovery for geotechnical analysis and design.

In order to maintain the high level of quality our clients expect whilst maintaining the optimum rate of production, we’ve selected coreline set (i.e. linered) T6-116 barrels as our standard equipment. The thinner kerf of the T6 allows for finer cutting and flush control whilst maximising the diameter of the recovered core. This is particularly useful where the client requires a nominal core diameter of 100mm, but does not need the larger diameter borehole which tends to accompany thicker kerfed P & S series barrels.

Southern Testing Field Operations complements this equipment with a range of other coreline set barrels, both metric and imperial for bore diameters between 100mm and 160mm, with a full suite of casing. We carry basket catchers and a range of bits to allow us to core anything from sand to granite and have equipped our rig with a set of dynamic sampling tubes to allow us to dry sample superficial material prior to casing to rockhead and switching to a flushed coring method.

We have the capacity to drill to a maximum depth of 50m below ground level in stock. Our 205 rig is set up for combined air / water flush and we have a minimum-loss recirculated water flush system for use on sensitive sites where mess is an issue.

We have recently completed the drilling of a    series of rotary cored boreholes at a site in Crawley, West Sussex which is earmarked for redevelopment with a 5 storey building. The geology at the site was Weald Clay which tends to a mudstone at depth. The rotary cores were drilled using Southern Testing’s Commachio 205 rig.

Geotechnical Laboratory Testing was carried out in-house on the recovered cores. Rock testing included Point Load Index tests and Uniaxial Compressive Strength to ISRM2007. The Point Load test is an index test for the strength classification of rock materials and cores can be tested either axially or diametrically. The Uniaxial Compressive Strength test requires preparation of suitable core samples which are loaded axially to failure. The compressive strength is then calculated.

The results of testing were used in pile design for the structure and formed part of our detailed geotechnical site investigation report.

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