Scale dependence of shear strength from direct shear test for a coarse granular material

Abstract

Due to the excellent shear resistance, the coarse-grained soil often serves as a material of a filling structure like the embankment dam. However, the shear strength of this geomaterial measured by the direct shear test has obvious scale dependence. The scale effect needs to be eliminated when evaluating the shear strength parameters for design. This study employs a superimposition–nest type of direct shear apparatus to investigate the scale dependence of the shear resistance for a natural coarse granular material, which will be used as a filling material of the rock fill dam in a hydropower station. The present apparatus can vary the diameter and height of specimen. The gap thickness can be kept constant during shearing. There are seven sets of different size tests performed in total. The variations of the shear strength indices plotted according to the test results reveal the influence of the specimen size on the soil shear resistance. The mechanism of the scale effect is discussed, and the lower limits of the diameter and height of specimen as well.

Keywords:

• Direct shear test
• Shear strength
• Scale effect
• Specimen size
• Coarse-grained soil