Analysis of the preloading effect on shear strength for dense sandy soils A discrete element modeling

This paper presents a numerical study of the effect of preloading on the shear strength of dense sandy soils. For this purpose, a discrete elements modeling of the direct shear box test is developed. The model is based on the molecular dynamics method with circular-shaped elements. The intergranular contact normal forces are computed using the linear viscoelastic model whereas the tangential forces are computed through a viscoelastic perfectly plastic model. A rolling friction model is incorporated in order to take account of the damping in grains rolling movement. The sheared samples are built by pluviation. In a first series, the deposited samples are sheared under confining stresses of 50, 100 and 200 kPa. Then, the samples are sheared under the same confining stresses after a preloading-unloading cycle with different vertical preloads. The performed simulations reproduce well the features of shear tests on dense sands. Furthermore, they show that the preloading has a slight effect in the initial phase of shearing, i.e., before reaching the peak of shear strength. However, after having passed the peak, the desinterlocking of the grains results in a loss of the preloading history. Therefore, the shear strength and the critical void ratio become insensitive to the preload history.