Effects of specimen preparation method and particle flatness on strength properties of direct shear test

In order to examine the shear strength characteristics of direct shear tests on coarse-grained soil, the effects of the sedimentation angle α formed during specimen preparation and the specimen preparation method are investigated. For specimens prepared by the free-fall method, the shear resistance angle increases with the sedimentation angle regardless of the density of the specimen, and the rate of increase increases with the flattening of the particles. In addition, compared to the free-fall method, the specimens prepared by the ramming method have a larger particle inclination angle β, which is the angle between the shear plane and the particle long axis direction. This effect increases the number of particles that exhibit rotational resistance, which is a factor that increases strength, but it also causes the skeletal structure to become lower, regardless of the flatness ratio, which is a factor that decreases shear strength.