Effect of particle characteristics on granular friction evaluated by dual-slip-plane friction tests

Abstract The frictional properties of natural granular materials are important for understanding dynamic natural phenomena such as earthquakes and landslides. The coefficient of friction for natural granular materials varies significantly based on parameters including sliding velocity, normal stress, and experimental conditions (temperature, humidity, etc.). This variation makes it difficult to accurately assess the relative slip resistance of two granular materials under identical conditions. To address this issue, we present a novel experimental approach employing a rotary shear apparatus that applies shear stress to two samples simultaneously. In this study, we utilized this method to determine the slip resistance of 50 different granular materials selected through a tournament competition. Qualitative evaluation results showed that crushed oyster shells, composed of biogenic calcite, were the most slip-resistant material. It was also found that the highly ranked, slip-resistant materials are those with higher peak frictions. Factors contributing to higher friction differed significantly between natural and artificially crushed particles, with the peak friction for crushed particles being strongly influenced by angularity, flatness, specific surface area, and particle-size distribution. The significantly higher friction of crushed oyster-shell particles can be attributed to their composition, which includes particles of various angular shapes, such as needle-like and flat forms. The shape characteristics prevent particle rotation, increasing the number of contact surfaces with neighboring particles. Oyster shells are a cause for concern as an industrial waste product, but their high frictional force has a potential for secondary use as a soil conditioner and slip-resistant material.