Environmental Engineering Reference
In-Depth Information
Table 5.9.
Deficiencies in
in situ
testing.
Problem
Consequences
Remedy
Testing only at predetermined depths, e.g.
Poor identification of strata, poor selection of
Supervise full time and test at strata changes
etc., e.g. SPT, undisturbed tube sampling
strata to test and sample
as well as at pre-determined depths
1.5 m, 3 m, 4.5 m
SPT (and CPT) test in gravelly soils affected by coarse
Overestimation of SPT “N” value, with resultant
No real remedy. Just recognise the problem
particles
overestimation of relative density, underestimation
or seek other ways of estimating the
of compressibility
parameters
Not washing borehole carefully before water pressure
Joints remain clogged with drill cuttings, Lugeon
Take care in washing hole. Use clean water
testing
value underestimated
for testing
Lack of
in situ
permeability tests in soils
Contractual claims because “conditions are
Do appropriate
in situ
tests despite the costs
worse than contractor assumed”; gross errors in
involved
estimation of permeability
Estimation of permeability from particle size distribution
Underestimation of permeability because of
Only use “Hazen” type formulae in uniform,
mixing of finer layers. See Figure 6.55
clean fine-medium sand for which it was
derived
Use of pump-in permeability tests in soil, particularly
Gross underestimation of permeability due to
Use pump-out tests where soils are below
structured clay and in augered boreholes
smearing and clogging of fissures, root holes,
water table. Above water table use pits, with
sandy layers, (by factor of 10 to 10
3
).
the sides carefully cleaned to remove
smearing. Adopt “realistic” values for
design regardless of results
Use of seismic refraction survey to estimate rippability
Incorrect prediction of rippability,
Do seismic refraction correctly (see
contractual claims
Whiteley, 1988). Couple with geological
factors (see MacGregor et al., 1994 and
Stapledon, 1988b), and recognise estimates
are approximate in contractual
arrangements
Installation of “wells” instead of properly constructed
Measures phreatic surface, not pore pressure.
Install piezometers, properly sealed in
piezometers in boreholes
May over/underestimate pore pressures (see
borehole
Figure 20.12 and fell, 1987)
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