A new fracture and abrasion model of unbound granular materials using the discrete element method

Unbound compacted granular materials are common in layered structures such as road pavements. Their performance depends on mechanical and hydraulic properties, and these depend upon grain size distribution which changes according to the amount of particle crushing, that occurs due to static or dynamic loads. Abrasion changes a particle's shape, and fracturing divides the particle into a mixture of many small particles of varying sizes. In this paper a new abrasion and fracture model is proposed to help us understand and visualize the evolution of crushing caused by compression and shear in unbound granular materials. The model uses a numerical simulation with the discrete element method in two dimensions. New concepts are used in the particle failure model to simulate fracture and abrasion. Damage induced by stresses on a particle is used to calculate abrasion and to determine the time of fracture of a particle. Damage is calculated using Miner's rule plus a combination of Griffith's fracture criterion and the fatigue law of material. Tensile strength in a particle is estimated as a function of material properties using an adaptation of Weibull's theory. Abrasion is calculated using a particle packing model developed by De Larrard. A cumulative distribution function of the beta distribution is used for determining the final grain distribution. This model is validated with the gyratory compaction test using three granular materials used in road pavements in and around the city of Bogotá.