Shear Strength of Unsaturated Soils - Unsaturated Soil Mechanics in Engineering Practice - page 560

Figure 11.50 Stress path followed during constant-water-content triaxial test.

Figure 11.51 Stress conditions at various stages of consolidated undrained triaxial compression
test with pore pressure measurements.

11.6.4 Undrained Test
The pore-air and pore-water phases are not allowed to drain
in the undrained test. The lack of drainage applies when the
confining pressure is applied and when the deviator stress is
applied to the soil specimen (Fig. 11.53). The excess pore-air
and pore-water pressures developed during the application of

the confining pressure can be related to the isotropic confin-
ing pressure through use of the B pore pressure parameters
provided the pore pressures are measured. The soil specimen
may change volume due to compression of pore-air during
the application of confining pressure. The soil has a net con-
fining pressure σ 3 −

u a and a matric suction u a − u w after