(3) Below Groundwater Table. When sampling below groundwater table,
maintain borehole full of water or drilling fluid during cleanout, during
sampling and sample withdrawal, and while removing cleanout tools. Where
continuous samples are required, casing should remain full for the entire
(4) Soft or Loose Soil. Sampling of a soft or loose soil directly
below a stiff or compact soil in the same tube should be avoided.
Discontinue driving of sample tube when a sudden decrease in resistance
3. UNDISTURBED SAMPLES FROM TEST PITS. Hand trimmed samples may be
obtained in test pits, in test trenches, or in surface exposures. Samples
so obtained are potentially the least disturbed of all types of samples.
The basic procedure consists of trimming out a column of soil the same size
or slightly smaller than the container to be used in transportation, sliding
the container over the sample, and surrounding the sample with wax. Tight,
stiff containers that can be sealed, and are not readily distorted, should
4. ROCK CORES. Rock is sampled with core barrels having either
tungstencarbide or diamond core bits as listed or described in Table 9 and
The suitability of cores for structural property tests depends on the
quality of individual samples. Specify double or triple tube core barrel
for maximum core recovery in weathered, soft, or fractured rock. The
percentage of core recovery is an indication of soundness and degree of
weathering of rock. Carefully examine core section for reasons for low
recovery. More details on rock recovery can be found in Chapter 1.
5. SAMPLING OF DISINTEGRATED ROCK TRANSITION ZONES. General guidance on
sampling of rock with various degrees of disintegration is given in Table 11
(modified from Reference 7, Sampling of Residual Soils in Hong Kong, by
6. OFFSHORE SAMPLING. For water depths less than about 60 feet, land
type soil boring equipment can be used on small jack-up platforms, small
barges or barrel floats. Floating equipment requires suitable anchoring and
is limited to fairly calm sea conditions. For deeper water or more extreme
seas, larger drill ships are required to obtain quality undisturbed samples.
See Table 12 for common underwater samplers. Numerous types of
oceanographic samplers, both open-tube and piston types, are available for
use from shipboard. These depend upon free-fall penetration and thus are
limited in depth of exploration. The quality of samples obtained by most
oceanographic samplers is not high because of their large length to diameter
ratio. For detailed information on underwater sampling equipment see
Reference 8, Underwater Soil Sampling, Testing and Construction Control,
ASTM STP 501, and Reference 9, Seafloor Soil Sampling and Geotechnical
Parameter Determination - Handbook, by Lee and Clausner.