Drilling without introducing water into the ground
Drilling with hollow stem flight augers allows borings, tests and instrument installation to be carried out dry, with no use of water or drilling fluids. The borehole remains fully cased by the augers, which preserves the walls and the soil to be sampled.
What hollow stem auger drilling is
The system is made up of hollow flight augers, with inner rods and a pilot bit. Drilling advances with the plugged assembly and, once the target depth is reached, the inner assembly is withdrawn, leaving the borehole cased by the augers. Because the method requires no water or drilling fluids, it does not introduce moisture into the soil nor alter the pore pressure of the ground being investigated.
Plugged assembly
The hollow augers advance with inner rods and a pilot bit; the assembly drills dry with the plugged tip.
Borehole cased by the augers
The flights themselves act as continuous casing, preserving the borehole walls.
Withdrawal of the inner assembly
Once the target depth is reached, the inner assembly is withdrawn, leaving the borehole cased and open for the operation.
Test, sample or instrument
SPT is performed, an undisturbed sample is collected with a Shelby tube or piston sampler, or piezometers are installed through the inside of the borehole.
The test in the field
Where the hollow stem auger comes in
| Borings and tests | SPT and special tests inside the cased borehole |
|---|---|
| Sampling | Collection of undisturbed samples with a Shelby tube or stationary piston sampler, even at greater depths |
| Instrumentation | Installation of piezometers and monitoring wells |
| General services | Geotechnical and environmental services in general |
The advantage of the method and the site standard
Why drill dry
- Suited to dams and works where introducing water into the ground is undesirable.
- Preserves the borehole walls through the continuous casing of the augers.
- Maintains the natural moisture and pore pressure conditions of the soil.
- Favours the recovery of quality undisturbed samples.
Safety and operation
- Ready for high-demand environments: mining, industry and ports.
- Organised, signed work front with an HSE procedure in place.
- Own crews and fleet, including night shifts.
Technical summary
| Method | Hollow flight augers with inner rods and pilot bit, plugged assembly |
|---|---|
| Drilling | Dry, with no water or fluids, borehole cased by the augers |
| Sampling | Undisturbed with a Shelby tube or stationary piston sampler, including at depth |
| Instrumentation | Installation of piezometers and monitoring wells |
| Application | SPT, special tests, environmental services, dams |
Sectors and project types
Bulletin 16: Hollow Auger
Dry drilling with hollow augers: when continuous casing preserves the ground and the sample.
Dry drilling for your project
Tell us the project context, we will put together the investigation plan and the quote. Or call +55 11 4195-8385.