Ren, Zeng-Le; (2021) Investigating the micromechanics of soil reinforced with recycled tyres using the Discrete Element Method. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This PhD program aims to provide insights into the behaviour of tyre reinforced sand, and to further the understanding of the reinforcement mechanisms. The discrete element method (DEM) using the software PFC3D version 5.0, is used to investigate the micro- mechanics of tyre-reinforced sand based on pull-out tests. A series of numerical direct shear tests have been performed. A full investigation of the individual particle shape descriptors (e.g., elongation index, flatness index, convexity and roundness) is presented, highlighting their influence on the macroscopic behaviour (e.g., failure mode and volumetric response). MorphologI G3 at UCL helps to obtain the quantitative particle shape information on Fujian Standard Sand. The sand information is incorporated in the results of particle shape studies to propose a representative particle shape for Fujian Standard Sand to model direct shear tests, leading to the calibration of pure sand. Then, a new three-dimensional DEM model for tyre rubber is developed based on uniaxial tensile tests. The model can capture the key volume change characteristics of tyres with a Poisson’s ratio of 0.5 independent of the tyre dimensions. Tyre rubber is modelled using body-centred-cubic (BCC) packing with linear inter-particle bonds. Next, a systematic parametric study is presented, which includes the effects of different packings, particle overlapping, particle radii and sample aspect ratios on the mechanical response of the tyre model using Young’s modulus and Poisson’s ratio. The DEM parameters are set to match corresponding experimental Young’s modulus data, completing the calibration of tyre. Lastly, the tyre – sand interface coefficient friction is calibrated from numerical and laboratory interface direct shear tests. All DEM parameters are used in tyre reinforced sand pull-out tests simulations. Micro analyses (such as particle displacement, velocity, contact force) presented in simulations show that the DEM tyre-sand pullout test simulation can capture the progress failure of tyre rubber during the pull-out process, and the intrusive capabilities of the discrete element method are used to gain insight into the reinforcement mechanisms between tyre and sand.

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