Effects of shear rate on shear strength and deformation characteristics of coarse-grained soils in large-scale direct shear tests

The strength and deformation of soils play an important role in the stability of slopes and subgrades. In order to analyze the influence of shear rate on shear strength and deformation characteristics of coarse-grained soils, the strength and deformation of coarse-grained soils under different shear rates are investigated by use of the THE-1000 lab large-scale direct shear apparatus. The experimental results indicate that the curves of shear stress versus shear displacement present themselves to be strain-softening ones under different shear rates. While the samples are sheared at the rate lower than 5 mm/min, the correlation coefficient is ideal. With the increase of the shear rate, the internal friction angle tends to decrease and ranges from 27.8° to 22.8°, and the interlocking force changes in the range between 90.30 to110.2 kPa. The breakage ratio and the maximum amount of shrinkage increase with the decrease of the shear rate or the increases of vertical stress. In other words, shrinkage occurs easily under a low shear rate. The essential reason why the shear strength shows a high value under a low shear rate is that the broken pieces of coarse particles fill the pores, which consist of the coarse particles, resulting in the increase of density of the soil samples.