Environmental Engineering Reference
In-Depth Information
Figure 5.11.
Large diameter hollow auger drill rig (courtesy CMEC).
It is not good practice to specify drilling programmes in detail before geotechnical map-
ping and logging of test pits and/or trenches is well advanced or completed. By this time,
understanding of the geological situation should be sufficient to allow boreholes to be
aimed at answering specific geological and/or engineering questions.
5.9.3
Auger drilling
The most common type of drilling in cohesive soils uses a spiral flight auger to penetrate
and remove the material below the surface. The simplest form is the hand auger which is
usually restricted by the physical effort involved to about 3 m.
Most augers are machine driven - and range from portable to large truck-mounted
hydraulic drill rigs (Figure 5.11).
The common auger rig equipped with either 100 mm or 150 mm diameter solid or hol-
low flight augers, can reach up to 30 m in soil strength materials. A steel blade “V” bit will
penetrate most fine-grained soils and extremely weak rocks but usually refuses on coarse
gravel or weak strength rock (Table 2.4). A tungsten-carbide “TC” bit will grind slowly
through weak and medium strong rock.
Auger drilling allows the logging of disturbed material collected from the flights during
drilling. By removal of the augers it is practical to regularly recover tube samples and
carry out
in situ
testing of the material properties.
Auger drilling is suited to the investigation of areas with thick soil deposits which
extend beyond the practical limit of pits or trenches. It does not provide the same amount
of data on soil structure but can supplement other information. In many cases it is used as
