Sp. Wright et al., OBSERVATIONS ON SOIL PERMEABILITY, MOLDING MOISTURE-CONTENT AND DRY DENSITY RELATIONSHIPS, Quarterly Journal of Engineering Geology, 29, 1996, pp. 249-255
Increasing use of the coefficient of permeability as a quality control
parameter for earthworks, in particular for landfilling, has resulted
in many engineers looking to predict coefficients. of permeability fo
r clays from more widely available but often widely scattered data. In
a number of cases this has led erroneously to the interpretation of t
he moisture content-coefficient of permeability relationship as the di
rect inverse of the moisture content-density relationship. This paper
re-examines the original theories proposed for movement of water throu
gh soils of differing grain size and goes on to show that extrapolatio
n of the permeability-density relationship for granular soils to finer
grained soils is incorrect. Laboratory permeability tests were conduc
ted on four different soil types using the falling head permeameter to
investigate the relationships between permeability, dry density and m
oulding moisture content for each soil. Coefficients of permeability w
ere determined for moisture contents up to the liquid limit of the soi
l. It is shown that a minimum value of permeability is obtained close
to optimum moisture content and that this is maintained to within sens
ible engineering limits for moisture contents up to that of the liquid
limit. Results obtained for predominantly granular soils confirm that
permeability is a function of density but, for more cohesive soils, p
ermeability is unaffected by changes in moisture content wet of optimu
m. Conclusions emphasise that to achieve minimum possible coefficients
of permeability there is a need for soil water content at placement t
o be at or slightly above optimum moisture content and for pelletizati
on of clay material.