TM 5-818-1 / AFM 88-3, Chap. 7
may depend on drilling equipment available and
The area ratio should be less than 10 percent for
laboratory facilities where tests will be performed.
undisturbed sampling.
Undisturbed samples are
(1) Undisturbed samples.
Any method of
commonly taken by thin-wall seamless steel tubing from
2 to 3 inches in diameter and lengths from 2 to 4 feet.
taking and removing a sample results in a stress change,
Undisturbed samples for shear, triaxial, and
possible pore water change, and some structure
consolidation testing are commonly 3 inches in diameter,
alteration because of displacement effects of the
but 5-inch-diameter samples are much preferred. An
sampler. Careful attention to details and use of proper
indication of sample quality is the recovery ratio, Lr ,
equipment can reduce disturbance to a tolerable amount.
defined as follows:
Sample disturbance is related to the area ratio A, ,
Lr =
Length of recovered sample
(4-3)
defined as follows:
Length sample tube pushed
2
2
Ar = D0 - D1
X 100 percent (4-2)
2
A value for Lr < 1 indicates that the sample was
D1
compressed or lost during recovery, and Lr > 1 indicates
where
that the sample expanded during recovery or the excess
D0 = outside diameter of sampler tube
soil was forced into the sampler.
D1 = internal diameter of the cutting shoe
(2) Representative samples. Samples can be
through which the sample passes (commonly the cutting
obtained by means of auger or drive-sampling methods.
edge is swedged to a lesser diameter than the inside
Thick-wall, solid, or split-barrel drive samplers can be
tube
wall
thickness
to
reduce
used for all but gravelly soils. Samples taken with a
Table 4-3. Recommended Minimum Quantity of Material for General Sample Laboratory Testing
Minimum Sample Required
a
Test
lb (Dry Weight)
Water content
0.5
Atterberg limits
0.2
Shrinkage limits
0.5
Specific gravity
0.2
Grain-size analysis
0.5
Standard compaction
30.0
Permeability
2.0
Direct shear
2.0
4-in.-diam consolidation
2.0
1.4-in.-diam triaxial (4 points)
2.0
2.8-in.-diam triaxial (4 points)
8.0
6-, 12-, or 15-in.-diam
Discuss with laboratory
triaxial (4 Points)
Vibrated density
Discuss with laboratory
a
Fine grained (all minus No. 4 sieve). For material containing plus No. 4 sieve sizes, the sampling requirements should
be discussed with the laboratory. In the final analysis, it is the responsibility of the engineer requesting the tests to
ensure that adequate size samples are obtained. Close coordination with the testing laboratories is essential.
U. S. Army Corps of Engineers
4-4
Previous Page
