A method to determine contact parameters for particulate geomaterials: a guide to inter-particle experiments and their analysis

The prevalence of discrete element simulations necessitates a robust understanding of contact between granular particles. The inter-particle apparatus has been used in several past studies to characterise the contact behaviour of sands, ballasts, and rock particles. However, the problems related to compliance, out-of-plane forces, and resolution of true normal and tangential forces have not yet been completely solved. Most of these problems can be attributed to the unknown orientation of the plane of contact between two particles. This article describes methods to obtain accurate contact data by reducing compliance and provides analyses of various test stages. Additionally, an accurate contact normal is derived in tangential sliding, accounting for out-of-plane force and vertical-horizontal displacement profile. The closed-form solution for normal and tangential forces is also derived, along with contact traces on each particle. The efficacy of these solutions is presented through an example test on Leighton Buzzard sand.