TABLE OF CONTENTS The triaxial test was briefly introduced in Sec. 8.5. The triaxial test apparatus is used extensively in the laboratory testing of cohesive soil. The triaxial test procedure is to place a cylindrical specimen of cohesive soil in the center of the triaxial apparatus, seal the soil with a rubber membrane, subject the soil to a confining fluid pressure, and then shear the soil specimen by increasing the vertical pressure. The types of laboratory tests that require the triaxial apparatus are classified according to the soil specimen drainage conditions, as follows:
Unconsolidated undrained triaxial compression test
Consolidated drained triaxial compression test
Consolidated undrained triaxial compression test
Consolidated undrained triaxial compression test with pore water pressure measurements
Because the data are of limited use, the unconsolidated undrained triaxial compression test is rarely used in practice. Likewise, the consolidated drained triaxial compression test is also rarely used in practice because the shearing of the cohesive soil in a drained state takes too long. The consolidated undrained triaxial compression test and the consolidated undrained triaxial compression test with pore water pressure measurements are identical, except that the latter test records the pore water pressure during shearing. The consolidated undrained triaxial compression test with pore water pressure measurements is by far the most popular of the four triaxial tests because it can provide both the shear strength in terms of total stresses ( c and ) as well as the shear strength in terms of effective stresses ( c
