Soft-rigid granular mixtures: Role of particle shape and rolling resistance in response under compressive loads

Abstract

Mixtures of recycled tyre aggregates and common granular geo-material such as gravel and sand have been widely used for various applications in geotechnical engineering, such as backfill, lightweight construction geomaterial and pavement subbase layers. The mechanical properties and characteristics of various soft-rigid granular blends has been extensively studied in the past. The main objective of these studies is to determine suitable mix designs for different applications and provide a better understanding of material response under applied loads. Experimental and numerical studies indicate the paramount importance of particle interaction at the microscale on the response of the soft-rigid granular mixtures at the macro scale. The stark contrast in stiffness (or flexibility) of soft tyre particles to rigid sand or gravel particles, means that in the soft-rigid mixtures under shearing or compressive loads, the deformation of soft tyre particles and continuous change of shape and contact area and hence constant evolution of frictional resistance plays an important role in the behaviour of these blends. In the present research mixtures of gravel and tyre particles in a range of volume ratios and size ratios were modelled using DEM (discrete element method) and calibrated to match one-dimensional compressibility experimental data obtained by the team. The effect of the shape of soft particles on the compressive response of soft-rigid granular mixtures is studied through rolling resistance in DEM. The role of rolling friction is studied in detail. Rolling resistance is found to be an important parameter to simulate the behaviour of the particle shape of these mixtures. Microscopic studies like spin analysis and share of contact force is performed to understand the observed response better. However, the increase in rolling resistance value beyond a calibrated value is found to have little impact on the macroscopic behaviour of these mixes.

Keywords

• recycled tyre aggregates
• soft-rigid granular mixtures
• rolling resistance
• discrete element modelling