Observations and findings on mechanical and plasticity behavior of sand-clay mixtures

This paper presents effects of particle size distribution and plasticity on geotechnical properties of sand-clay mixtures. Two different clay types (kaolinite and bentonite) were mixed with different-sized clean sand at mixture ratios of 0 to 100% with increasing 10% by dry weight. An intensive series of standard compaction, Casagrande, fall cone, and plastic limit (w(P)) tests were performed on specimens. Experimental results showed that the maximum dry density (rho(dmax)) values of the mixtures increased up to 10% clay content (threshold clay content) then decreased with increasing clay content. Besides, optimum water content (omega(opt)) values of the mixtures decreased up to around 10-20% of clay content and then increased continuously. It was found that fall cone liquid limits were 2-4% higher than obtained from the Casagrande device. The undrained shear strength at liquid limit is approximately 2.19 kPa, but, though the undrained shear strength at plastic limit has a wide range in comparison with liquid limit (17-636 kPa), as its recommended value, 143.95 kPa was proposed by the researchers. Moreover, results also reveal that consistency limits of specimens are governed by the content and type of clay and grain size distribution of the sand-clay mixtures. Finally, some equations were proposed between various findings (i.e., optimum water content-maximum dry density, plasticity index (PI)-optimum water content, undrained shear strength (S-u)-liquid limit (w(L))) that were derived from the test results.