Investigation of Sand Particle Breakage Using X-ray Micro-tomography

基於X射線微斷層掃描的砂土顆粒破碎研究

Student thesis: Doctoral Thesis

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Author(s)

  • Budi ZHAO

Detail(s)

Awarding Institution
Supervisors/Advisors
Award date25 Nov 2016

Abstract

Particle breakage is of fundamental importance for the understanding of the mechanical behaviour of sand and is relevant to many geotechnical engineering challenges such as low pile capacity in carbonate sands and large settlement of high rock-fill dams. To data the micromechanics of particle breakage has not been well understood. The aim of this study is to explore how the external and internal morphology of sand particles influences particle breakage, and quantitatively describe the evolution of microscale properties (e.g., particle size and particle shape) during particle breakage.

The material investigated was Leighton Buzzard sand (LBS) and highly decomposed granite (HDG), which have distinct external and internal morphological characteristics. Novel mini-loading apparatuses were developed to perform in-situ compression tests within laboratory X-ray micro-tomography (μCT) scanners. Both single particle crushing tests and oedometer tests were performed with a scanning resolution between about 3 µm and 12 µm. A series of image processing and analysis techniques were utilised to obtain both qualitative and quantitative results. Particularly, the linkage between particle breakage and particle shape evolution was investigated. A novel framework was proposed to quantify 3D particle shape with respect to particle form, roundness and compactness. New 3D roundness indexes were formulated from the local curvature on reconstructed triangular surface mesh.

The primary factors in determining the fracture patterns of the LBS and HDG particles were found to be particle morphology and initial microstructure, respectively. Versatile fracture patterns deviating from simple vertical splitting were observed, particularly in HDG particles. Fractal theory was implemented to interpret the evolution of particle size distribution due to fragmentation. Fragments are more irregular than initial particles in terms of form, roundness and compactness. The surface area measured from CT data was utilised to explore different energy dissipation mechanisms.