A popular and cost-effective ground investigation drilling method

Cable Percussion Drilling (also referred to as Shell and Auger drilling) is the UK’s most popular and cost-effective ground investigation technique that spans back hundreds of years.

The rig is typically trailer mounted and towed to the site and between borehole locations, using a standard 4×4 vehicle.

Once in position, the rig is erected as a 7m high tripod where a winch and cable system repetitively lift and drop a hammer to drive the drilling rods into the ground.

The end of the drilling rod is fitted with either a ‘clay cutter’ in cohesive soils, or a ‘shell’ (or bailer) for non-cohesive material. If hard ground or obstructions are encountered, a chiseling tool is used in an attempt to pass the obstruction.

Depending on the expected ground conditions and investigation requirements, the borehole can be drilled to either a 6-inch (150mm) or 8-inch (200mm) diameter.

Steel casing is often installed as the borehole progresses. The steel casing also seals the borehole, allowing for the collection of water samples from different horizons at increasing depths without cross-contamination.

Boreholes can be drilled to depths of 60m to 90m in good conditions.

The nature of Cable Percussion Drilling provides disturbed samples; however, intact ground samples can be obtained from thin-walled piston samples such as UT100 and U100 samples in soft normally consolidated soils.

These drilling rigs are also capable of carrying out Standard Penetration Testing (SPT) during the advancement of the borehole.

On completion of drilling, the boreholes can be used for Soakage Testing, or installed with instrumentation to monitor ground movement, groundwater levels, water quality, and gas.