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 ERDC TN-DOER-N5
July 2000
bottom to top of the specimen). This test, developed by Cargill (1983), has been described in detail
by Poindexter (1987, 1988).
Samples of site water should be collected for use in mixing and diluting the sediments (for
self-weight consolidation testing, if needed). Because the salt content of a sediment and its pore
water can significantly affect the engineering properties of the material, it is necessary to use the
proper concentration of salt in the pore water to accurately simulate the field behavior of the material;
this is most easily done by using water from the dredging/disposal site. If there is a significant
difference between salinity at the dredging and disposal sites, it is recommended at this time that
disposal site water be used if the sediment will drop freely through the water column upon disposal.
If compressible materials are encountered below the CAD cell, these materials should be tested
according to ASTM D 2435 (standard oedometer test) (ASTM 1999c) to determine their compressi-
bility. If compressible capping material will be used at the CAD, this material should be tested in
the oedometer, possibly supplemented by the self-weight test if field void ratios indicate it is needed.
Permeability Determination. Permeability of fine-grained soils is usually determined by a
falling head permeability test, which is run in conjunction with the (oedometer) consolidation test.
The procedure for this test is given in ASTM D 2435 (ASTM 1999c) and EM 1110-2-1906,
Appendix VII, Part 8 (Headquarters, USACE, 1986). When a permeability test is run on dredged
material, care must be taken with these very soft materials to prevent consolidation caused by the
force of water seeping through the sample (known as seepage consolidation).
As an alternative to running a permeability test, the permeability may be calculated from consoli-
dation properties by using the following relationship (Lambe 1951; Terzaghi, Peck, and Mesri
1996).
T50 H 2 γ wα v
af
k=
(1)
1+ e t
where
k
= permeability, ft/sec
= time factor = 0.197
T50
H
= average height of soil sample for load increment, ft
γw
= unit weight of water, lb/ft3
αv
= average coefficient of compressibility = -∆e/∆σ′
e
= average void ratio for load increment
t = time, sec
permeability of the soil specimen in the consolidation test for each load increment. Average values
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