Geology Reference
In-Depth Information
Spring-loaded
(retractable)
cutting shoe
Plastic liner
Rotary drive
Cutting bit
Flush
(water or
foam)
Flush
Sample
In weak
ground
cutting shoe
pushed into
'soil'
In rock, soil cutter
retracts and rotary
bit takes over
Schematic, not scale
Many parameters are obtained for design by laboratory testing, as
discussed in
Chapter 5,
but the potential for disturbance is obvious,
as discussed earlier, especially for granular soil that disaggregates
when not con
ned. There are therefore many reasons for attempting
to test soil and to a lesser extent rock in situ. Most tests are conducted
in boreholes, but some are conducted by pushing the tools from the
ground surface or from the base of a borehole to zones where the soil is
relatively undisturbed. A self-boring pressuremeter, suitable for clay
and sand, drills itself into the ground with minimal disturbance before
carrying out a compression test at the required level.
The SPT is probably the most commonly used in situ test, whereby
the number of blows to hammer a sample tube into the ground is
