Environmental Engineering Reference
In-Depth Information
7.3. Recap of the basic Barcelona model
The BBM is an elastoplastic model and it regards suction as an independent
variable, as for the stress.
In a plane S/P (suction: pressure) an elastic zone is delimited by a suction
increase (SI) line and a loading collapse (LC) curve (see Figure 7.3). They are two
yield surfaces. SI describes the plastification by suction, whereas LC describes the
plastification by stress. Thus, when increasing suction under constant stress, before
touching SI, only elastic strain occurs. On the other hand, once SI is touched,
elastoplastic strains occur.
S
SI
1
LC
Swelling
2
Collapse
Elastic zone
3
P
Figure 7.3.
Yield surfaces SI and LC and description of the
phenomena of swelling and collapse
The LC curve has a double function: it is the border between elasticity and
plasticity upon loading, and the border that separates the zone of swelling from the
zone of collapse upon wetting. Indeed, when wetting a soil by following the path 1-
2-3 in Figure 7.3, before the LC line is touched (1-2), swelling of elastic nature is
produced. By contrast, once the LC line is touched (2-3) collapse of a plastic nature
takes place.
It can easily be seen that under low stresses it is the swelling that prevails; the
reverse occurs under strong constraints. This description corresponds well to
experimental observations.
