Table 7.15.

Rotosonic/sonic drilling

Roto-/sonic drillingMethodApplicationsLimitations
Graphic
  • Wheeled or tracked mounted equipment which vibrate sampling tubes to recover a near-continuous soil sample;

  • 150–250 mm diameter;

  • Depth 100 m+ depending on plant;

  • >75 m per day achievable with large rigs;

  • Working area 2 m by 6 m required with 4–6.5 m clear headroom.

  • Sites where unrestricted vehicle access can be gained. Tracked mounted rigs may be deployed on sloping/rough terrain;

  • Near-continuous disturbed and intact samples;

  • Permits SPTs and borehole vane testing;

  • Rapid penetration rates;

  • Suited to most soil types including dense granular soils and over-consolidated tills;

  • Permits installation of simple monitoring wells;

  • May be applicable to some marine situations from a fixed vessel (e.g. jack-up barge).

  • Poor sample recovery possible in loose granular and very soft soils;

  • Sonic-only rigs are likely to provide a degree of disturbance to cohesive soils; use as Class 1 samples should be considered with care;

  • Vibration and noise associated with the driving process;

  • The use of a ‘dry drilling method’ can ‘bake’ soils rendering them unsuitable for testing;

  • Bonding in weak rocks can be totally destroyed;

  • Some sonic rigs do not have the capacity to insert casing.

Cost factor: low to medium
Relevance to glacial/periglacial depositsSome disturbance of small-scale features and ‘baking’ of the core surface may occur but otherwise a good technique; can provide an excellent recovery of continuous core making detailed logging viable. As the addition of water is not required in drained granular soils, retention of fines and detailed bedding structure provides additional benefits. Will penetrate cobble beds with ease and has been known to penetrate through igneous boulders. Samples may not be considered suitable for some advanced geotechnical testing where their particle bonding has been disturbed.