Effects of particle shape on shear modulus of sand using dynamic simple shear testing

The shear modulus of granular materials, such as sand, is a fundamental mechanical property that is affected by various factors, including particle shape. Understanding the effects of particle shape on the shear modulus is crucial for predicting the behavior of these materials in various geotechnical applications. This study investigated the effects of particle shape on the secant shear modulus of dry sand through dynamic simple shear testing. Firstly, the monotonic behavior of sand was investigated, and then samples were subjected to cyclic simple shear tests. The latter tests were performed for twelve different testing scenarios, defined by different vertical stresses and cyclic stress ratios (CSRs) in constant-stress and controlled-stress modes. For each scenario, five cyclic tests were performed, with each successive test performed on the same sand reconstructed from its previous cyclic test. A total of 25 randomly selected sand particles, collected before the first, second and fifth tests, were employed to investigate the effects of particle shape on the secant shear modulus. For this purpose, three shape parameters, including roundness, sphericity and regularity, were used to quantify the particle shape characteristics. After each cyclic test, hysteresis loops were established, and the secant shear modulus was determined. Test results indicated that the sand had a dilative behavior and successive cyclic loading negatively affected the shape of the sand particles, with the particles progressively becoming slightly rounded with successive cyclic testing. All three particle shape parameters increased by approximately 5–10%, and as such, the changes in particle shape severely reduced the secant shear modulus.