Environmental Engineering Reference
In-Depth Information
In situ
measurements of
k
values are made for evaluations of:
Percolation rates for liquid-waste disposal systems.
●
Necessity for canal linings (as well as for designing linings).
●
Seepage losses beneath and around dam foundations and abutments.
●
Seepage losses in underground-cavern storage facilities.
●
Groundwater control during excavation.
●
Associated Phenomena: Capillary, Piping, and Liquefaction
Capillary
is the tendency of water to rise in “soil tubes,” or connected voids, to elevations
above the groundwater table. It provides the moisture that results in heaving of foun-
dations and pavements from freezing (frost heave) and swelling of expansive soils.
Rating criteria for drainage, capillary, and frost heave in terms of soil type are given in
Piping
refers to two phenomena: (1) water seeping through fine-grained soil, eroding the
soil grain by grain and forming tunnels or pipes; and (2) water under pressure flowing
upward through a granular soil with a head of sufficient magnitude to cause soil grains to
lose contact and capability for support. Also termed boiling or liquefaction, piping is the
cause of a “quick” condition (as in quicksand) during which the sand essentially liquefies
(see also
Section 8.3.2
for piping).
“Cyclic” liquefaction
refers to the complete loss of supporting capacity occurring when
dynamic earthquake forces cause a sufficiently large temporary increase in pore pressures
in the mass (see
Section 11.3.3).
3.3.2
Estimating the Permeability Coefficient k
General
Basis
Since
k
values are a function of basic and index properties, various soil types and forma-
tions have characteristic range of values. Many tables and charts have been published by
various investigators relating k values to geologic conditions, which are based on numer-
ous laboratory and field investigations and which may be used for obtaining estimates of
k
of sufficient accuracy in many applications.
Partial Saturation Effects
In using tables and charts, one must realize that the values given are usually for saturated
conditions. If partial saturation exists, as often obtained above the groundwater level, the
voids will be clogged with air and permeability may be only 40 to 50% of that for satu-
rated conditions.
Stratification Effects
In stratified soils, lenses and layers of fine materials will impede vertical drainage, and
horizontal drainage will be much greater than that in the vertical direction.
Relationships
Permeability characteristics of soils and their methods of measurement are given in
Table
3.11.
Typical permeability coefficients for various conditions are given in the following
