The rate at which water is transmitted through a saturated specimen of concrete under an externally maintained hydraulic gradient is defined as the coefficient of permeability
. It is inversely linked to durability in that the lower the permeability, the higher the durability of concrete (Joshi and Lohtia 1997).
where [zeta] represents the jump coefficient of permeability
(JCP), which can be calculated by [k.sub.b]/[k.sub.a], where [k.sub.b] and [k.sub.a] represent the permeability values measured at the peak state and residual state, respectively (see Figure 4).
This requires an understanding on the coefficient of permeability
within the soil, but features of unsaturated soil are subject to constant change.
The Figure 2 introduces the results of the four repetitions of the permeability tests for the hydraulic gradients 15, 66, 85 and 140, showing the number of daily readings after the stabilization of the water flow in the specimens versus the coefficient of permeability
The coefficient of permeability
, k, is one of the most important parameters for studying nonlinear properties of soil, and a linear correlation between the void ratio e and lg k is valid for the most common clays , which can be expressed as follows:
Falling head permeameter was used to determine the coefficient of permeability
of the samples.
The measurement method enables calculating the coefficient of permeability
[k.sub.T] on the basis of the determined theoretical model.
The average discharge was used for determining the coefficient of permeability
. The steady state was normally attained within a test period of 7 days to 15 days.
However, at intermediate values of water coefficient of permeability
rainwater will infiltrate to a certain degree and will not entirely drain away.
And by the pore pressure ratio [B.sub.q]  and by the side friction [f.sub.s] to determinate the permeability coefficient of soil, the coefficient of permeability
coefficient was directly determined by using the cone tip resistance and side friction [7, 8].
The hydraulic conductivity of the compacted specimens symbolized in terms of the coefficient of permeability
([kappa]) was determined by using a falling-head water permeameter.