Geoenvironment Impact Mitigation and Management - Sustainable Practices in Geoenvironmental Engineering - page 365

Double Mariotte tube
system can be
raised or lowered to
change the effective
height h of the fluid
permeating the
sample

Double Mariotte tube system

Height h

Air entry at
elbow inlet

Test sample in rigid permeameter

Calibrated flask collecting permeant

FIGURE 10.4
Water entry experiment with constant hydraulic head h for permeating luid in a rigid permeameter.

Since the Darcy model for determination of the permeability coeficient k from experi-
ments such as those shown in Figure 10.4 does not consider the properties of the permeant
and the microstructure of the soil, Yong and Mulligan (2004) have proposed a relationship
that uses a modiication of the combined form of the Poiseuille and Kozeny-Carman rela-
tionships. This takes into account the inluence of the properties of pore channels deined
by the structure of a soil, and the fact that the wetted soil particles' surface area is con-
trolled by the microstructure of the soil. The relationship obtained is shown as:

3

Cn
TS

γ ∆

∆

s

vki == *

(10.1)

22

l

η

w

where k* is the PKC (Poiseuille-Kozeny-Carman) permeability coeficient, which considers
permeant and soil microstructure properties (= Cn

3 2 2
γ/ ), C s is the shape factor, with
values ranging from 0.33 for a strip cross-sectional face to 0.56 for a square face (Yong and
Warkentin (1975) have suggested that a value of 0.4 for C s may be used as a standard value,
with a possible error of less than 25% in the calculations for an applicable value of k* ), i is
the hydraulic gradient, which is the ratio of the potential or hydraulic head difference Δψ
between the entry and exit points of the permeant, and the direct path length Δ l of the soil
mass being tested, T is the tortuosity, which is the ratio of effective low path Δ l e to thick-
ness of test sample Δ l and which is quite often taken to be ≈ √2, γ and η are the density and
viscosity of the permeating luid, respectively, n is the porosity of the unit soil mass, and
S w is the wetted surface area per unit volume of soil particles.

TS

s w