Effects of Fine Content on Undrained Shear Response of Sand–Clay Mixture

The aim of this paper is to investigate the influence of fines content on the undrained shear behavior of sand–clay mixtures with fines contents at 0%, 5%, 10%, 12.5%, 15%, 17.5%, 20%, 22.5 and 25%. The shear strength of the mixture has been evaluated in terms of skeleton void ratio and transitional fines content. Materials used are poorly graded sand from the eastern coast of Famagusta, and swelling clay from Nicosia, North Cyprus. Direct shear (DS) tests were used to evaluate the shear strength parameters of sand–clay mixtures at constant strain rate of 1 mm/min under normal stresses of 27.78, 55.56 and 83.33 kPa. The DS test results indicated a unique relation between the transitional fines content and the angle of internal friction, in which the internal friction angle increased with increasing fines until reached maximum value of 45.68° at the transitional fines content (10%). Therefore, additional fines content increased the shear strength up to the transitional fines content after which decrement occurred for all normal stresses.