Exploring the microscale mechanics of shear strength weakening in granular soils induced by vibrations: A DEM study

The weakening of shear strength in granular soils under various vibrations is a common phenomenon, though its underlying mechanisms remain unclear. In this study, the macroscopic and microscopic shear behaviors of granular soils under vibration are investigated using the discrete element method (DEM). Specifically, the effects of vibrational acceleration a, vibrational frequency f and confining pressure sigma(n) on the dynamic mechanical properties of granular soils are examined. Dense and loose specimens composed of spherical particles are subjected to triaxial compression tests until the critical state is reached. At the macroscopic level, the results show that the degree of shear strength weakening and reduction in void fraction exhibit an approximately linear relationship under different vibration conditions. On the microscopic scale, anisotropic analysis sheds light on the mechanisms behind shear strength weakening from two perspectives. First, the weakening is primarily driven by reductions in the contact normal anisotropy a(n), normal contact force anisotropy a(c), and tangential contact force anisotropy a(t), with their contribution follows a(n) > a(c) approximate to a(t). Second, a linear relationship is observed between the stress ratio q/p' and contact normal anisotropy within the strong and non-sliding contacts a(c)(sn) during vibration phase (i.e., q/p' = 0.62a(c)(sn) ). Thus, the decrease of shear strength due to vibration is fundamentally linked to the reduction of a(c)(sn) .