Effect of Sample Size and Shape on Critical State

Abstract

This paper presents a numerical study of the effect of sample size and sample shape on the critical state condition of a granular material. The sample consists of binary-disperse ellipsoids. Samples were created by gravity deposition technique which is similar to the dry pluviation sample preparation method in physical testing. Same generation method was used to generate these samples but the initial sample dimensions were different. The grain size distribution is identical. The samples are either a cube or a rectangular prism. Samples were compressed isotropically with a confining pressure of 100 kPa. Then, conventional triaxial compression tests were performed until the critical state (ultimate state) was reached. Triaxial compression tests along different principal directions were also carried out. We present typical macroscopic result including stress-strain relationship and volumetric behavior. The friction angle and void ratio at critical state were examined. It is found that the conventional defined critical void ratio is related to the sample size. However, the friction angle at critical state is unique.