Civil Engineering Reference
In-Depth Information
Figure 11.7
A state boundary surface for soil.
reconstituted soil can occur. If soil with a state on the surface is unloaded the state
moves inside the surface and, on reloading the state will move back to, but not outside,
the surface. Thus, the state boundary surface can also be a yield surface like that shown
in Fig. 3.16. If the boundary surface is a yield surface then while the state is on the
surface there are simultaneous elastic and plastic strains, but if the state is brought
inside the boundary surface, by unloading, the strains are assumed to be purely elastic.
This is a highly idealized model for soil behaviour and we now know that there are
inelastic strains when the state is inside the boundary surface. These aspects of soil
stress-strain behaviour will be considered in Chapter 13.
The idealized behaviour of soil during isotropic compression and swelling was con-
sidered in Secs. 8.2 and 8.3 (see Figs. 8.2 to 8.6) and is illustrated in Fig. 11.8.
This shows a sequence of loading and unloading from A to D where the overcon-
solidation ratios are the same but the specific volumes are different. Between B and C
the state was on the normal compression line (i.e. on the state boundary surface) and
Figure 11.8
Elastic and plastic compression.
