Rate Dependent Response of Unbonded Granular Media Subjected to Direct Shear Test

Abstract

The mechanical behavior of granular media is key to structural safety, but designs often ignore the influence of shear rate, creating a potential risk. The primary engineering implication is that rate-independent models are potentially non-conservative for structures under dynamic or variable loading conditions, such as pavements and seismic regions. This study addresses this gap by quantifying the rate-dependent shear strength and deformation characteristics of granular materials. To achieve this, a comprehensive series of direct shear tests was performed on quartz aggregates, a widely used construction material. Samples were subjected to a range of shear rates under various constant normal loads, while peak shear strength, residual strength, and volumetric strain (dilatancy) were systematically measured. The results demonstrate that shear strength increases with both shear rate and applied normal load. Interestingly, this strain rate effect was observed to diminish significantly at higher confining pressures, revealing a critical coupling between confinement and loading rate. Furthermore, the rate of dilatancy was shown to be directly dependent on both the applied shear rate and the initial packing density of the material. These findings provide the necessary data to build better engineering models, which will improve the safety and accuracy of geotechnical designs.