Shear response and frictional properties of soil mixtures at different dry weight proportions

Abstract

On a specific purpose to investigate and evaluate an important mechanical property of natural soil mixtures being shear response and frictional characteristics, an extensive laboratory experimental program has been conducted that consisted of a series of direct shear tests on various soil mixtures, including sand (S), silt (M) and clay (C), at different dry weight proportions [(i) S:100% - M:0% - C:0%; (ii) S:50% - M:50% - C:0%; (iii) S:50% - M:0% - C:50%; (iv) S:50% - M:25% - C:25%]. The experimental findings of the testing program have shown that the measured values of two crucial engineering design parameters such as the peak (t(peak)) as well as the residual (tresidual) shear strengths for the soil mixtures are strongly influenced by the present soil type such that the detected values of tpeak, tresidual increase with an increase in sand content in the mixture whereas the attained values of t(peak), t(residual) decrease with an increase in clay content in the mixture. Further, adding silt into sand-clay mixture improves strength characteristics such that the values of tpeak, tresidual become greater. On the other hand, adding silt into pure sand diminishes frictional resistance such that the values of t(peak), t(residual) become lower. Consequently, it is seen that soil particle size (i.e. grain size) plays an important role on the shear strength behavior of the natural soil mixtures. Moreover, the displacement (dpeak) required to reach peak shear strength (t(peak)) was also determined as a result of the direct shear tests. As such, the detected values of dpeak become larger with higher clay content available in the mixture, while the obtained values of dpeak become smaller with higher sand content existing in the mixture. Therefore, it is concluded that the higher the clay content, the mixture exhibits relatively more ductile shear behavior, whereas the higher the sand content, the mixture displays relatively more brittle shear response.