Environmental Engineering Reference
In-Depth Information
FIGURE 2.62
Split-barrel sample of sand.
and an increase in wall friction to aid in retrieval. The rods and sampler are rotated clock-
wise about two revolutions to free the sampler by shearing the soil at the sampler bottom.
The sample is withdrawn slowly from the hole with an even pull and no jerking. In soft
soils and loose granular soils, the sampler bottom is capped just before it emerges from the
casing fluid to prevent the soil from falling from the tube.
Shelby Tube Sampling
A thin-wall tube is fitted to a head assembly (
Figure 2.63)
that is attached to drill rod. An
“O ring” provides a seal between the head and the tube, and a ball check valve prevents
water in the rods from flushing the sample out during retrieval. Application is most satis-
factory in firm to hard cohesive soils. In firm to stiff soils, the tube is pushed into the soil
by a steady thrust of the hydraulic system on a rotary drilling machine using the machine
weight as a reaction. Care is required that the sampler is not pressed to a distance greater
than its length.
