| Author: | Huo, Yingxu |
| Title: | Micro-mechanical study of the particle shape effect on shearing of sands |
| Advisors: | Leung, Andy (CEE) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | Sand -- Mechanical properties Shear strength of Soils Soil mechanics Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Civil and Environmental Engineering |
| Pages: | xviii, 216 pages : color illustrations |
| Language: | English |
| Abstract: | Particle shape is a pivotal property of natural sands that varies from angular to rounded. While its influence on some shearing behaviours has been clearly documented, such as the critical state friction angle, coordination number, fabric anisotropy and maximum and minimum void ratios, disagreements exist in previous studies about its influence on micro-mechanics and how it affects shear strength and volumetric responses of sands. In particular, the unique micro-mechanical role of particle shape is not recognized or distinguished from spherical particles incorporated with rolling resistance (µr). In addition, the influence of particle shape on maximum dilatancy, which is a key attribute of peak strength of sands upon shearing, is not well understood. This thesis adopts the discrete element method (DEM) to investigate the influence of particle shape on macro- and micro-mechanical behaviours of sands upon shearing and to address the above problems from the perspectives of fundamental soil mechanics and the implications for engineering practice. The influence of particle shape on the micro-mechanics is examined through simulating triaxial shearing of sands at various porosities and confining stresses. To simulate particle shapes in DEM models, Toyoura sand particles are scanned by a micro-computed tomography (µCT) scanner whose morphological information is stored as triangulated surface facets and is reconstructed in the models as clumps comprised of a number of overlapping spheres. A systematic modelling and calibration approach is proposed to facilitate the simulations with realistic particle shapes. It involves a comparison of shape parameters between the scanned particles and the modelled clumps, an evaluation of the distribution of shape parameters for clumps composed of varying numbers of pebbles, and the calibration of appropriate micro-parameters for these clumps. The calibration process entails a comparison between numerical simulations and experimental results using a multiple linear regression method. The results demonstrate the merits of modelling realistic particle shapes and the deficiency of simplifying particle shapes as spheres with µr. The unique role of particle shape is illustrated from both macro and micro responses of the shearing simulations, through the discussions in terms of contact sliding, particle rolling, fabrics and contact networks. The influence of particle shape on dilatancy is investigated through modifications to the saw-blades model which incorporate particle shape effects and conceptual models of particle pairs subject to shearing, where the relationship between particle kinematics and dilatancy is presented in detail. It is shown that particle shape affects dilatancy by the different packing structures, contact orientations and whether the particles move relative to another through sliding or rotation. The mechanism proposed in the conceptual models is then demonstrated through triaxial shearing simulations of particles with various angularities, where each simulation consists of ten different shapes of Toyoura sand particles with similar shape parameters. Two groups of triaxial shearing simulations are performed: one is performed at the same initial void ratio e0 and the other at the same initial relative density Dr0. The variations of shearing and volumetric responses with particle shape in each group are presented, which can be explained from the observed micro-mechanical aspects and are in agreement with the findings from the conceptual models. This thesis demonstrates the capability of modelling particle shape in reproducing the realistic shear responses of sands. It enhances the understanding of the unique role of particle shape in shearing responses. It clarifies the influence of particle shape on shear dilatancy and suggests taking into account the particle shape effect in estimating the strength-dilatancy relation. |
| Rights: | All rights reserved |
| Access: | open access |
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