Investigation of loading rate effect on the shear strength of clay-sand mixture in triaxial test

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The strength behavior of soil is affected by strength parameters including soil cohesion and its internal friction angle. These parameters are influenced by factors such as soil density, soil type, loading rate, moisture content, confining pressure and Etc. In this paper, the effect of loading rate on shear strength behavior of clay-sand mixtures is investigated using triaxial test. In this research, 8 types of clay:sand composite materials with weight ratios of 100:0, 80:20, 60:40, 40:60, 30:70, 20:80, 10:90 and 0:100 were used. To investigate the effect of loading rate, samples were subjected to non-uniform loading rates of 0.1, 1 and 5 mm/min with defined load pattern. In this study, three confining pressures of 100, 300 and 500 kPa were used. The results of this study show that, depending on the amount of confining pressure, the sudden change in loading rate has different effects on the strength of samples with different percentage of clay-sand combination. Deviator stress variations as well as the slope of the stress-strain curve depend on the amount of sand at the moment of sudden change in loading rate. In other words, changes in deviator stress and slope of the stress-strain curve are directly related to the amount of sand from one limit to the next. This limit of sand is 40% for low confining pressure (100 kPa) and 20% for higher confining pressure (300 and 500 kPa)