Influence of the Particle Size on the Flow Potential and Friction Index of Partially Saturated Sandy Soils

The particle characteristics of sandy soils play a major role in the shear strength response in terms of the flow potential and friction index of partially saturated sandy soils. In this context, a series of an experimental study based on monotonic undrained triaxial compression tests were conducted on two groups of sandy soils with three maximum particle sizes (D-max = 4.00 mm, 2.00 mm, and 1.00 mm) and two different effective diameters (D-10 = 0.08 mm and 0.25 mm). The samples were reconstituted in the laboratory with a wet deposition method at an initial relative density of (D-r = 25%), tested under three different Skempton's pore pressure parameters (B = 20%, 50%, and 90%) and subjected to a constant confining pressure (P '(c) = 100 kPa). The obtained test results indicate that the maximum particle size (D-max) has a significant influence on the shear strength response of the tested sandy soil samples. Indeed, the undrained shear strength increases with the increase of the maximum particle size and it is more significant in the case of the lower Skempton's pore pressure parameter (B = 20%) compared to the higher and medium ones (B = 50% and B = 90%). However, the maximum particle size can be considered a reliable parameter to predict the steady-state and the instability friction angle, and also it has a noticeable effect on the friction index and the flow potential of sandy soils. Finally, Skempton's pore pressure parameter could be related to the steady-state and the instability friction angle, the friction index and the flow potential of sandy soils under consideration.