Environmental Engineering Reference
In-Depth Information
(a)
(b)
(c)
Fluid under pressure
"Soft" formations
"Hard" formations
Fluid return
Drill rod
or pipe
Ball bearing
hanger
Sliding valve
open
Valve seal
Spring
protects
tube from
excessive
pressure
Static
fluid vented
to bore
Sliding valve
closed
Cutter barrel
Full-gage
bore needs
no reaming
Tube screw
Shelby tube
fully extended
All fluid
diverted to
annular space
High-velocity
flush keeps
cutting area
clean
Drill fluid
flushes
cuttings
Sample
protected
from fluid
FIGURE 2.68
Operation of the Pitcher sampler: (a) down the hole; (b) sampling; (c) recovery. (Courtesy of Mobile Drilling Inc.)
Auger Samples
Completely disturbed cuttings from the penetration of posthole diggers (hand augers,
Table 2.12)
,
continuous-flight augers, or large-diameter augers are brought to the surface
when the auger is removed from the hole. In cohesive soils they are useful for soil identi-
fication, moisture content, and plasticity index tests.
Retractable Plug Sampler
One-inch-diameter tubes containing slightly disturbed samples are obtained in soft to firm
organic and cohesive soils suitable for soil identification and moisture content measure-
ments (Table 2.12).
Test Pit Samples
High-quality undisturbed
block
or “chunk” samples or small cylinder samples in softer
soils with some cohesion are taken from test pits. Block samples are particularly useful in
soils difficult to sample UD such as residual soils. Strong cohesive soils are sampled by
carefully hand-cutting a block from the pit walls. The sample is trimmed by knife and
encased in paraffin on the exposed sides. The block is cut loose from the pit, overturned,
and the remaining side is coated. It is then sealed in a box for shipment to the laboratory.
Very large samples are possible.
Weaker soils with some cohesion are carefully hand-trimmed into a small cylinder and
sealed. The method has been used to obtain samples for density tests in partially saturated
silty or slightly clayey sands.
