TM 5-815-5/AFM 88-5, Chap 6/NAVFAC P-418
samples of sand that have been segregated or con-
c. Soil testing.
taminated with drilling mud during sampling opera-
(1) All soil and rock samples should be carefully
classified, noting particularly those characteristics
tions do not give reliable results. In addition, the
that have a bearing on the perviousness and stratifica-
permeability of remolded samples of sand is usually
tion of the formation. Soil samples should be classified
considerably less than the horizontal permeability kh
in accordance with the Unified Soil Classification Sys-
of a formation, which is generally the more significant
tem described in MIL-STD-619B. Particular atten-
k factor pertaining to seepage flow to a drainage sys-
tem.
tion should be given to the existence and amount of
fines (material passing the No. 200 sieve) in sand sam-
(3) Where a nonequilibrium type of pumping test
ples, as such have a pronounced effect on the perme-
(described in app C) is to be conducted, it is necessary
ability of the sand. Sieve analyses should be made on
to estimate the specific yield Sy of the formation,
representative samples of the aquifer sands to deter-
which is the volume of water that is free to drain out
of a material under natural conditions, in percentage
of total volume. It can be determined in the laboratory
D10 size may be used to estimate the coefficient of
by:
permeabililty k . The gradation is required to design
filters for wells, wellpoints, or permanent drainage
(a) Saturating the sample and allowing it to
drain. Care must be taken to assure that capillary
systems to be installed in the formation. Correlations
between k and D10 are presented in paragraph 3-4.
stresses on the surface of the sample do not cause an
(2) Laboratory tests depicted in figure 3-2 can be
incorrect conclusion regarding the drainage.
used to determine the approximate coefficient of
(b) Estimating Sy from the soil type and D10 size
permeability of a soil or rock sample; however, perme-
of the soil and empirical correlations based on field
abilities obtained from such tests may have little rela-
and laboratory tests. The specific yield can be com-
tion to field permeability even though conducted
puted from a drainage test as follows:
under controlled conditions. When samples of sand are
100Vy
(3-1)
Sy =
distributed and repacked, the porosity and orientation
V
where
of the grains are significantly changed, with resulting
Vy = volume of water drained from sample
modification of the permeability. Also, any air en-
V = gross volume of sample
trapped in the sand sample during testing will signifi-
The specific yield can be estimated from the soil type
cantly reduce its permeability. Laboratory tests on
(From "Ground Water Hydrology "by D. K. Todd, 1959, Wiley & Sons,
Inc. Used with permission of Wiley & Sons, Inc.)
Figure 3-2. Permeameters: (a) constant head and(b) falling head.
3-3
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