Environmental Engineering Reference
In-Depth Information
TABLE 3.11
Permeability Characteristics of Soils and Their Methods of Measurement
a
Coefficient of Permeability
k
(cm/s) (log scale)
10
2
10
−
7
10
1
10
10
−
1
10
−
2
10
−
3
10
−
4
10
−
5
10
−
6
10
−
8
10
−
9
Drainage
Good drainage
Poor drainage
Practically impervious
Very fine sands; organic and
inorganic silts; mixtures of sand,
silt, and clay; glacial till
stratified clay deposits; etc.
Clean sand
"Impervious soils,
e.g.,homogeneous
clays below zone
of weathering
Clean gravel
Types of soil
Clean sand and
gravel mixtures
"Impervious soils" which are modified by
the effects of vegetation and weathering
Direct testing of soil in its original position
(e.g. field-pumping tests)
Direct
determination
of coefficient
of permeability
Constant-head permeameter
Falling-head permeameter
Computations
from grain size distribution, porosity, etc.
Indirect
determination
of coefficient
of permeability
Computations
from time rate of consoli-
dation and rate of pressure
drop at constant volume
Horizontal capillarity test
a
After Casagrande, A. and Fadum, R.E., Soil Mechanics Series, Cambridge, MA, 1940 (from Leonards, G.A.,
Foundation Engineering, McGraw-Hill Book Co., New York, 1962, ch. 2).
tables: rock and soil formations,
Table 3.12;
some natural soil formations,
Table 3.13;
and
various materials for turbulent and laminar flow,
Table 3.14.
Values of
k
for granular soils
in terms of gradation characteristics (
D
10
,
C
R
, curve type) are given in
Figures 3.13
and
3.14,
with the latter figure giving values in terms of
D
R
.
Rock masses:
Permeability values for various rock conditions are given in Table 3.12. A
useful chart for estimating the effect of joint spacing and aperture on the hydraulic con-
ductivity is given in
Figure 3.15.
3.3.3
Laboratory Tests
Types and Applications
Constant-head tests
are used for coarse-grained soils with high permeability.
Falling-head
tests
are used for fine-grained soils with low permeability.
Consolidometer tests
may be used
for essentially impervious soils as described in
Section 3.5.4.
Constant- and Falling-Head Tests
The two types of laboratory permeameters are illustrated in
Figure 3.16.
In both cases,
remolded or undisturbed specimens, completely saturated with gas-free distilled water,
are used. Falling head tests on clay specimens are often run in the triaxial compression
