Technical Notes

Dilatancy and Friction Angles Based on In Situ Soil Conditions


Dilatancy influences almost all aspects of the behavior of granular material, ranging from shear strength to stress-strain behavior. However, there is no practical method for estimating the dilatancy angle based on in situ soil properties, although the variables that influence dilatant behavior are well-known. This paper attempts to link the dilatancy angle to preshear mean effective stress and relative density for cohesionless soils. Accordingly, it may be possible to estimate the dilatancy angle by using variables that can be measured or calculated during the soil exploration phase of a design project. For this purpose, an experimental study is conducted on Silivri sand and the obtained results are used to quantify the relationship between dilatancy angle and preshear soil properties. An equation for the dilatancy angle is proposed that requires only two unit-independent soil constants, which can be obtained by conducting triaxial or plane strain tests. Moreover, the proposed dilatancy equation can be combined with a linear relationship between friction angle and dilatancy angle to form a new equation that can be used to estimate the peak friction angle. Thus, a new equation is developed that allows the calculation of the peak friction angle from preshear soil properties. Finally, for verification purposes, the proposed equations for dilatancy and peak friction angles are tested by using available data on other sands and the results are compared with the predictions of available dilatancy equations in literature.

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