Volume 6 – Geotechnical Manual, Site Investigation and Engineering ...

Chapter 1 PLANNING AND SCOPE
Table 1.3 Relative Merits of In Situ and Laboratory Testing
In situ testing
Test results can be obtained during the
course of the investigation, much earlier
than laboratory test results
Appropriate methods may be able to test
large volumes of ground, ensuring that the
effects of large particle sizes and
discontinuities are fully represented
Estimates of in situ horizontal stress can be
obtained
Drainage boundaries are not controlled, so
that it cannot definitely be known whether
loading tests are fully undrained
Stress path and or or strain levels are often
poorly controlled
Tests to determine effective stress strength
parameters cannot be made, because of the
expense and inconvenience of a long test
period
Pore pressures cannot be measured in the
tested volume, so that effective stresses are
unknown.
Advantages
Disadvantages
Laboratory testing
Tests are carried out in a well-regulated
environment
Stress and strain levels are controlled, as
are drainage boundaries and strain rates
Effective strength testing is straightforward
The effect of stress path and history can be
examined
Drained bulk modulus can be determined
Testing cannot be used whenever samples
of sufficient quality and size are obtainable,
for example, in granular soils, fractured
weak rock, stoney clays
Test results are only available some time
after the completion of fieldwork
The ground investigation planner requires a detailed and up-to-date knowledge of both laboratory
and in situ testing, if the best choices are to be made. Table 1.4 gives a summary of the local current
situation — but this will rapidly become out of date. Whatever is used depends upon the soil and
rock encountered, upon the need (profiling, classification, parameter determination), and upon the
sophistication of geotechnical design that is anticipated.
1-14 March 2009