Question

Describe the essential features of Consolidated-Undrained, Unconfined-Undrained, and Unconfined-Compression tests. Feel free to use sketches.

Answer 1

1)Consolidated undrained (CU)

In CU test ,undrained strength is determined after void ratio has been changed from initial value by consolidation.The undrained strength is thus function of its void ratio.

This type of test is used to check stability under sudden unloading such as dewatering or draw down.

2) unconsolidated undrained test (UU test)

In this drainage is not allowed during 1st and 2nd stage .When specimen is placed under traaxial cell,the intake pore water pressure is negative due to capillary tension.Total stress being zero and effective stress positive .After application of all round pressure ,the effective stress in the specimen remains unchanged because under undrained condition ,increase in all around pressure results in equal increase in pore water pressure.this type of test is used in sudden loading such as rapid construction and checking short term stability.

3) Unconfined compression test(UCS)

No confining pressure is applied.and is used for cohesive soil and only one Mohr circle is obtained at failure.

UCS test uses simple equipment ,can be conducted in field easily .Used for rapid assessment of consistency of soil for classification of clays and also used to determine the sensitivity of the clay