Civil Engineering Reference
In-Depth Information
there must be some relationship between the rate at which the loads are applied, the
rate of drainage and the behaviour of the soil and pore pressure.
6.9 Drained loading, undrained loading and
consolidation
The relative rates at which total stresses are applied and at which the seepage takes
place are of critical importance in determining soil behaviour. The limiting conditions
are illustrated in Figs. 6.10 and 6.11.
Figure 6.10(a) illustrates an increment of total stress
applied slowly, over a long
period of time. This could represent loading in a laboratory test or in the ground. If
the loading is applied very slowly water will be able to seep from the soil as the total
stresses increase. There will be no change of pore pressure, as shown in Fig. 6.10(c),
and the volume changes will follow the change of loading, as shown in Fig. 6.10(b).
σ
Figure 6.10
Characteristics of drained loading.
Figure 6.11
Characteristics of undrained load-
ing and consolidation.
