Secondary compression of clay in consolidation and undrained shear tests

Secondary compression plays an important role in oedometer tests on clay and peat. The consolidation period, therefore, must have some influence on the undrained behaviour of clay in direct shear and triaxial compression tests. Hence, secondary compression in soft clay should not be neglected for the settlement and stability of structures even in the field. In the opening sections of the present paper, the influencing factors on the coefficient of secondary compression are investigated on the basis of long-term consolidation tests. Additionally, a single loading oedometer test is proposed instead of the conventional oedometer tests, as it will shorten the period of ordinary oedometer tests. In the latter part of the paper, a method is presented for predicting the change in the undrained strength of clay due to secondary compression, and an analysis of direct shear and triaxial compression tests proves that this method is particularly useful for practical purposes. Also, it is suggested from the results of triaxial consolidation tests that the stress anisotropy and the drainage direction in a clay cylinder would affect the undrained strength as well as the secondary compression. Finally, it is pointed out that the undrained strength obtained from the results of direct shear tests is of the same significance as those from K o - consolidated triaxial compression tests.