Drained angle of internal friction from direct shear and triaxial compression tests

The angle of internal friction of sands from direct shear tests and plane strain tests is reported to be higher by about 2-8 degrees compared to the triaxial compression tests. However, information about the comparison for the case of fine grained soils is scarce in the literature. In the present study a comparison of the results of a series of direct shear tests and triaxial compression tests on three fine grained soils is made. The angle of internal friction obtained from triaxial test is found to be more than that obtained from direct shear tests for fine grained soils. The likely reason is attributed to the presence of plate shaped clay sized particles through experiments carried out on sand mixed with plastic discs.