Abstract:To study on the size effects on the strength of cohesionless coarse-grained soils under the direct shear condition

direct shear tests with the same specimen size were carried out for cohesionless coarse-grained soils with different maximum grain sizes. The maximum grain sizes were 40mm、20mm、10mm、5mm

and 2mm

respectively. There was the same void construction for soils with self-similar fractal structure in mass. The method of tin wires embedded vertically in specimens was used to measure the thickness of shear zones. Test results show that the shear strength and shear zone thickness increased with the increase in the maximum grain size. The size effect on strength were apparent when the maximum grain size is greater than 1/20 of the specimen height. The interlocking force and friction angle decreased with the increase in the logarithm of the ratio of specimen height to maximum grain size

the relationships between them being linear. The strong force chain took place easily because the number of particles in shear zone decreased with the increasing of the maximum grain size

it causing the size effect on strength of cohesionless coarse-grained soils under the direct shear condition.