Soil sampling with a double-tube hollow-stem sampling
system provides a method for obtaining continuous or intermittent
samples of soils for accurate logging of subsurface
materials to support geotechnical testing and exploration. A
wide variety of soils from clays to sands can be sampled. The
sampling systems can be particularly effective in dry soft to
stiff clayey or silty deposits but also can work well under
saturated conditions. Saturated cohesionless soils such as clean
sands may flow and cave during drilling (see Note 1). In many
cases, the HSA soil core sampling system can produce very
little disturbance to the sample and can provide samples for
laboratory tests for measurement of selected engineering properties.
Large-diameter soil cores, if taken carefully, can provide
Class C and D samples as described in Practice D4220. The
HSA systems can also provide disturbed samples of unsaturated
sands and gravels with some structure preserved. Full 5-ft
[1.5-m] long cores usually cannot be obtained in unsaturated
sands due to increasing side wall friction between the dry sands
and inside surface of the sample core barrel. Sample length of
2 to 2.5 ft. [0.60 to 0.75 m] is generally the limit of amount of
sample that can be recovered in unsaturated sands before the
friction between the sampler and the sand becomes too high
and causes blocking or plugging of the sampler. Shorter large
diameter core runs of 2.5 ft [0.75-m] with the 5-ft [1.5-m]
sample barrel system, or with a 2.5-ft [0.75-m] sample barrel
system, have generally proven to result in the best samples.