Experimental study of the direct shear mechanical characteristics of the sand with different granular diameter

DRS-1 high normal stress direct and residual shear apparatus was used to study the direct shear mechanical characteristics of the sand with different granular diameter under different normal stress. The results show that for three kinds of sand (coarse sand, medium sand and fine sand) the curve of shear stress-shear displacement presents strain softening when the normal stress, σ, is less than, or equal to, 1.6MPa, but strain hardening occurs when σ is greater than 1.6MPa. At the same time, the relation of shear stress and displacement of the sand is closed to that of the Clough-Duncan hyperbola when σ is greater than 1.6MPa. The mechanism of shear strength is various under different normal stress condition. The volume of the sand expands when the normal stress is low (e. g. 0.4MPa, 0.8MPa) and the energy that the volume expansion needs is predominant in the shear strength. On the contrary, the volume contraction of the sand is observed under high normal stress condition (e. g. 8MPa, 12MPa) and the energy that the grain breakage needs plays a main role in the shear strength. The shear stress shows a good linear correlation of the normal stress for different diameter granular, that is to say, all the shear strength increases evidently with normal stress.