Environmental Engineering Reference
In-Depth Information
Figure 7.13.
Ranges in effective stress failure envelopes for pure clay minerals and quartz (Olson,
1974).
values for several clay minerals, with varying electrolyte concentrations and for different
cations in the electrolyte.
It can be seen that:
-
At the same pore fluid adsorbed cations concentration, montmorillonite swells to a
greater void ratio and has a higher swelling index than illite, which in turn swells more
than kaolinite;
Exchange of Na by Ca in montmorillonite (smectite) significantly reduces swell
potential, but has only a minor effect on kaolinite;
-
Increase of concentration of Na causes a marked decrease in the swelling index of
montmorillonite, but no change in the swelling index of kaolinite.
-
These phenomena are to be expected given the large surface area, and higher negative
charge on the surface of montmorillonite, compared to illite and kaolinite.
7.5.3
Shear strength
The shear strength, parameters c
R (residual strength) are
dependent on the clay fraction percentage as shown in Figures 6.4 and 6.5. Clays with a
high clay fraction percentage exhibit lower shear strengths and a greater reduction from
peak to residual strength. As shown in Figure 6.5 and Figure 7.13 the shear strength is also
dependent on the types of clay minerals present, with lowest strength for pure montmoril-
lonites, highest for kaolinite. However for normal soils, the behaviour is also influenced by
the mixture of clay minerals present, and the presence of silt and clay sized particles.
,
(peak strength) and C
R ,
7.6
IDENTIFICATION OF DISPERSIVE SOILS
7.6.1
Laboratory tests
There are several laboratory tests which can be used to determine the dispersivity of a soil.
Search WWH ::




Custom Search