Abstract:

The significant particle size grading and particle breakage of deep soils are two major characteristics of super-high dumping sites. The particle breakage and shear strength of different coarse-grain contents were studied based on the refitted large-scale direct shear apparatus. The experimental results of particle breakage indicated that particle breakage index was very small when upright stress was lower than 400 kPa and increased obviously with the increase of upright stress that was higher than 400 kPa. The particle breakage index was very little at coarse-grain contents less than 46.0% and increased significantly according to the increasing of coarse-grained contents which was more than 46.0%. The relationship between particle breakage index and upright stress could be expressed by hyperbolic curve. The particle breakage of soil sample ,which was soaked for a long time in water, was remarkbale. The experiments studied on shear strength showed that the shear stress-strain curves were micro-softening model or micro-hardening model under low upright stress and were slight-softening model at higher upright stress when the coarse-grain contents was equal to 24.0%. At coarse-grain contents equal 78.0%, the shear stress-strain curves were softening model under low upright stress and slight-hardening model at higher upright stress. The shear strength envelope expressed nonlinear under higher upright stress. When the particle breakage index was small, the internal friction angles which were respectively fitted in the upright stress lower than and higher than 400 kPa changed little. With the obvious increment of particle breakage index, the internal friction angle of upright stress higher than 400 kPa was much smaller than that of upright stress lower than 400 kPa.

Key words: coarse-grain soil, large-scale direct shear apparatus, coarse-grain contents, particle breakage index, shear strength