Environmental Engineering Reference
In-Depth Information
Hole squeezing may occur in soft clays if the drilling mud is too thin.
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Plastic clays may remain along the casing walls if cleaning is not thorough.
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Hollow stem augers can cause severe disturbances depending on the rate of
advance and rotation, and the choice of teeth on the bit.
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Hollow-stem augers must be advanced with the plug in the auger prior to sam-
pling to prevent soil from entering the auger.
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Sampler Insertion
All ball check valves and other mechanisms should be working properly before the sam-
pler is lowered into the hole. The sampler should be lowered to the bottom immediately
after the hole is cleaned. Measurements of the total length of the sampler and rods should
be made carefully to ensure that the sampler is resting on the bottom elevation to which the
hole was cleaned and to avoid sampling cuttings. Since complete cleaning is usually not
practical, split-barrel samplers are seated under the rod weight and often tapped lightly
with the drive hammer; piston samples are forced gently through the zone of soft cuttings.
Soil Factors
Soft to firm clays generally provide the best “undisturbed” samples, except for
“quick” clays, which are easily disturbed.
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Air or gas dissolved in pore water and released during sampling and storage can
reduce shear strength.
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Heavily overconsolidated clays may be subject to the opening of fissures from
stress release during boring and sampling, thereby substantially reducing
strength.
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Gravel particles in a clay matrix will cause disturbance.
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Cohesionless granular soils cannot be sampled “undisturbed” in the present
state of the art.
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Disturbance in cohesive materials usually results in a decrease in shear strength
and an increase in compressibility.
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Sample disturbance and its effect on engineering properties are described in detail by
Broms (1980). See
Section 2.4.6
for sample preservation, shipment, storage, and extraction.
Split-Barrel Sampler (Split Spoon) (ASTM D1586-99)
Purpose
Split-barrel samplers are used to obtain representative samples suitable for field examina-
tion of soil texture and fabric and for laboratory tests, including measurements of grain-
size distribution, specific gravity, and plasticity index, which require retaining the entire
sample in a large jar.
Sampler Description
Split-barrel samplers are available with and without liners; the components are shown in
Figure 2.61.
O.D. ranges from 2 to 4 ½ in. A common O.D. is 2 in. with ¼ in. wall thickness
(1 ½ in. sample). Larger diameters are used for sampling gravelly soils. Lengths are either
18 or 24 in.
A ball check valve prevents drill pipe fluid from pushing the sample out during
retrieval. To prevent sample spillage during retrieval, flap valves can be installed in the
shoe for loose sands, or a leaf-spring core retainer (basket) can be installed for very soft
