Table 7.18.

Rotary sampling

Rotary samplingMethodApplicationsLimitations
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  • ‘Multi-function’ rotary/sampling rigs which can operate in various modes to suit soil/rock conditions;

  • In soft ground borehole is advanced using various auger systems or driven tube sampling;

  • In hard clays and rock borehole advanced using rotary coring systems;

  • Depth 30–50 m (smaller plant) and 100 m+ (larger plant and marine drill systems;

  • 10–50 m per day;

  • Working area 2 m × 6 m required with 4–5 m clear headroom (small units).

  • Sites where unrestricted vehicle access can be gained and that are relatively level;

  • Some tracked units can operate with slope gradients <30°;

  • Suitable for use in most soils from clays to sands or firm to hard clays and rock (in coring mode);

  • Installation of standard monitoring installations;

  • Depending on operating mode, most standard forms of sampling and in situ tests may be taken;

  • Applicable to most marine situations from a fixed vessel (e.g. jack-up barge) and drill ship.

  • Depends on operating mode adopted;

  • Difficulties may occur if made ground, water-bearing cohesionless soils or dense, very coarse granular soils are encountered;

  • ‘Liquefiable’ material may be drawn into hollow stem augers;

  • Use of solid stem and helical auger systems will provide disturbed samples only;

  • Difficult to install aquifer protection measures.

Cost factor: medium to high
Relevance to glacial/periglacial depositsOften the preferred method of drilling through thick sequences of till due to the depth that can be achieved, good sample recovery in clays and diamictons and the ability to progress through cobble beds and boulders. Continuous coring allows for detailed logging and samples for advanced geotechnical testing. High clast content will not limit recovery, however cobbles may become stuck in barrel leading to scrubbing of the core. Sand and gravel layers will often lead to zones of no recovery. Flush type should be considered as water and drilling muds will lead to blow-out and major disturbance of granular beds and lenses if encountered. Not suitable if extensive glaciofluvial sand and gravel is present above till, or below. In such circumstances a cable percussion starter hole may be required or the borehole terminated using a different technique.