Drive tube sampling

The drive samplers used on light rigs are illustrated in Section 4. All samplers must be driven into a clean stable bottom. In an auger drilled hole, some soils may require the addition of a little water so that the cuttings are picked up. Pressure sands may have to be stabilized.
• by filling the hole with dense mud
• by using the flexible centre plug or other methods as described in Section 4 of Chapter 7.
A standard 63.5 kg(140 lb) hammer or a bumper sub and the rod string, is used to drive the tube until full.
Care must be taken not to overdrive the sampler. The tool is then pulled lo recover the sample. The sample is removed and placed in a plastic bag along with a label. The bag is scaled
Care must be taken to measure and record exact depth measurements.
Table tool drive sampler: The main advantage of table tool operations is that hard bands and gravel can easily be penetrated and cased to allow operation of the sampler.
After clearing the hole with a piston type bailer, the sample tube is driven using the spudding action of the rig. The number of blows lo drive the tube is recorded. When recovered, the shoe is removed from the tube and the tube scaled at both ends.
The heavy driving causes disturbance to the outside of the sample. For laboratory testing a less disturbed. small sample can be cut from the centre of the 100mm(4 in) tube.
Top hammer driving: The hammer delivers continuous blows that improve recovery over cathead or hydraulically driven slide hammers. Compaction of the sample is on the order of 3 to 5 cm (1 3/6 - 2 in) in the 1.5 m (5 ft) core with minimal disturbance. More disturbance and compaction occur in cores with more extensive clay layers