Civil Engineering Reference
In-Depth Information
6.3.3 Boreholes
In most ground investigations, several boreholes are required and these are often taken down to many
metres in depth. Thus, specialist drilling equipment is required to form these. In the UK the operation is
usually carried out dry whereas in the USA wash boring techniques are more common.
Two main methods of forming boreholes exist:
cable percussion boring
and
rotary drilling
.
Cable percussion boring
This method is sometimes referred to as the
shell and auger
method. The equipment is shown in Fig.
6.3.
The principle of operation is:
●
the A-frame (which is transported to site in its collapsed state, towed by a 4-wheel drive vehicle) is
erected at the location of the borehole and stabilised;
●
the winch, powered by the portable diesel generator, lifts the cutting tool (Fig.
6.4)
towards the top
of the A-frame. In clay soils, the
clay-cutter
is used; in more sandy and gravelly soils the
shell
is used;
●
the winch brake is released and the tool is allowed to fall freely into the soil;
Pulley
Tripod
assembly
Diesel engine powered
direct drive free-fall winch
Cutting tool
Fig. 6.3
Cable percussion boring.
