Question

4. Explain the design conditions that consolidated drained (CD) and consolidated undrained (CU) tests try to simulate. Discuss the types of laboratory triaxial test that you would specify to determine the shear strength parameters in connection with the following field problems: (a) The stability of an embankment which is to be constructed on a thick layer of clay deposit within a relatively short duration; (b) The long-term stability of a slope in stiff fissured clay.

Answer 1

Consolidated Un - drained In first stage drainage is allowed hence consolidation can take place, and in 2nd stage no drainage is allowed when extra pressure (deviator stress) is applied. It is used to check the effect of impact loading. As an example at the end of construction excess pore water pressure will develop which will decrease the shear strength and with time shear strength will increase as excess pore water pressure becomes zero. Triaxial Test Triaxial compression tests can be conducted on sands and clays. Figure 1.34 a shows a schematic diagram of the triaxial test arrangement. Essentially, it consists of placing a soil speciman confined by a rubber membrane in a Lucite chamber. An all - round confining pressure (sigma_3) is applied to the specimen by means of the chamber fluid (generally water or glycerin). An added stress (Delta sigma) can also be applied to the specimen in the axial allowed