Environmental Engineering Reference
In-Depth Information
6
Shear strength, compressibility and permeability of
embankment materials and soil foundations
6.1
SHEAR STRENGTH OF SOILS
6.1.1
Drained strength - definitions
When a soil is sheared slowly in a drained condition (so that there is sufficient time for
dissipation of pore pressures induced by shearing), the stress displacement curves will take
the general form shown in Figure 6.1.
The behaviour is dependent on whether the soil has a high or low clay fraction (finer
than 0.002 mm) content and on whether it is normally consolidated (NC) or overconsol-
idated (OC), but has the following common features:
-A peak strength is obtained at a small displacement.
-A reduction of strength to the critical state or fully softened strength then occurs with
further displacement. For overconsolidated soils this is due to increase in water content
with dilation of the soil as it is sheared. The fully softened strength corresponds to
the critical state (Skempton, 1985), i.e. when continuing displacement occurs without
further change in volume or water content. Note that normally and overconsolidated
Figure 6.1.
Diagrammatic stress displacement curves at constant normal stress
n
(Skempton, 1985).
