Study on macro and micro shear strength of continuously graded and gap-graded sand

The particle gradation of sand has a significant influence on its shear strength,yet the similarities and differences between the effects of continuous and gap grading have yet to be fully explored.In this study,the discrete element method(DEM)was used to simulate biaxial tests on granular samples that were both continuously graded and gap-graded.The macroscopic analysis revealed that the shear strength of continuously graded sands increases initially and then decreases as the uniformity of particle size distribution decreases.On the other hand,the lack of medium particles in gap-graded sands amplifies the difference in particle size between coarse and fine particles,leading to a decrease in shear strength.Microscopically,both continuous and gap gradings affect the internal packing structure of the particle assembly,which consequently affects particle stress distributions,contact forces,coordination numbers,stress-induced anisotropies,and contact force networks,thus having an impact on the macroscopic shear strength.The global uniformity of particle size distribution was unidirectionally affected by continuous grading,while gap grading had a locally bidirectional influence.These findings provide a better understanding of the effects of particle grading on the macroscopic shear strength of sands.