The shear strength parameters in the case of saturated soils depend
very much upon the drainage conditions and therefore in the laboratory
shear test, the drainage condition expected in the field for a
particular problem should be simulated. Based on drainage condition the
shear tests are classified as following 3 types.
- Unconsolidated Undrained Test (UU test)
- Consolidated Undrained Test (CU test)
- Consolidated Drained Test (CD test)
1. Unconsolidated Undrained Test (UU)
Drainage is not permitted throughout the test. In the case of direct
shear test drainage is not permitted during the application of both
normal stress and shear stress. In the case of triaxial compression test
drainage is not permitted during the application of both cell pressure
and deviator stress. Since the test is conducted fast allowing no time
for either consolidation of sample initially or dissipation of pore
pressure in later stage, the test is also called quick test.
2. Consolidated Undrained Test (CU)
In this type of shear test the soil specimen is allowed to
consolidate fully under initially applied stress and then sheared
quickly without allowing dissipation of pore pressure. In the case of
direct shear test the specimen is allowed to consolidate fully under
applied normal stress and then sheared at high rate of strain to prevent
dissipation of pore pressure during shearing. In the case of triaxial
compression test the specimen is allowed to consolidate fully under the
applied cell pressure and then the pore water outlet is closed and the
specimen is subjected to increasing deviator stress at higher rate of
strain.
3. Consolidated Drained Test (CD)
In this type of shear test drainage is allowed throughout the test.
The specimen is allowed to consolidate fully under the applied initial
stress and then sheared at low rate of strain giving sufficient time for
the pore water to drain out at all stages. The test may continue for
several hours to several days.