SWGT have several tracked rigs that are transportable on the back of a van and are used for rapid drilling of boreholes up to around six metres depth for sampling and twenty metres or more for dynamic probing. We currently have two types of tracked rig, the standard 'Dart' rig with removable baskets that can access through doorways and an all terrain rig with expandable tracks, which is better suited to fields.

The tracked rigs are fitted with a Standard Penetration Test (SPT) trip hammer which drives the sample tubes into the ground and also performs SPT strength tests between sample runs. The rigs can be modified on site to house a coring attachment for diamond drilling through concrete or asphalt hard standing. A duplex casing system may be employed to support the hole when drilling through unstable soils that are likely to cause hole collapse.  It should be noted that the casing has limited depth due to the fact that the casing can only be driven into the ground via the hammer weight and cannot be surged to reduce friction as in the case of cable tool drilling.

The SPT hammer is also the same as used for super heavy dynamic probing. DPSH is often used to continue the borehole to depths where the sample tubes cannot reach or to provide information on the depth of hard strata for end bearing piles.

As an alternative to dynamic probing SWGT have developed a continuous CPT where a shortened cone is driven into the ground and a continuous SPT N value versus depth profile is obtained.

The sample is recovered within a one metre long plastic sleeve which gives a high quality 'core' of the soil. These tubes are generally split after recovery and logged and sub-sampled by the supervising geotechnical engineer.