Geological behavior of sand-fines mixtures in consolidated undrained triaxial test

Geological behaviors of clean sand with fines particles were investigated in this study. Consolidated undrained triaxial shear tests (CU) were carried out on sand specimens with various fines content in the range from 0% to 60%, by weight. Two initial conditions of samples, including a constant global void ratio, and a constant relative density, were used in this work. Specimens were prepared by the wet tamping method. The specimens were tested by three levels of confining pressure, including 50 kPa, 100 kPa, and 200 kPa to determine some behaviors such as stressstrain, pore water pressure-strain, peak deviator stress-fines content, stress paths. Results indicated that adding more fines content to the mixture causes some complicated behaviors. The shear strength decreased until a threshold fines content of 50%, for testing at the constant void ratio index; and thereafter, it gradually increases with a further increase in fines content. The pore water pressure (PWP) of all the sand-fines mixtures rapidly increases as the axial strain reaches a value in the range of 1 to 2% and then slowly increases and reaches a stable state with a strain greater than 8%. The stress path increases to reach the peak value and continues moving towards the stress origin. Finally, the results are expected to contribute a better understanding which respects to shear strength, geological behavior of the sand-fines mixtures. Keywords: fines content; sand-fines mixtures; undrained behavior; shear strength; triaxial test.