Advanced Investigation of Sand Particle Breakage Using Combined Nanofocus X-ray CT and Three-Dimensional Discrete Element Modelling

Description

Particle breakage is of fundamental importance to the mechanical behavior of sands and is related to many geotechnical engineering problems such as low pile capacity in carbonate sands and large settlement of high rock-fill dams. The source of particle breakage effects lies in the change made to the sand fabric during deformation process, a critical geometrical factor which governs the macroscopic sand behavior but must be evaluated using a microscopic approach. Despite considerable research dedicated to the micromechanics of sands associated with particle breakage, the nature of particle breakage is not well understood. Particularly no linkage is established between the particle breakage behavior and the intrinsic particle microstructure. Consequently, prediction of particle breakage and quantification of its effects on the sand behavior remains a difficulty.In view of the above deficiency, we propose an advanced investigation of the behavior of sand particle breakage using combined techniques of high-resolution nanofocus X-ray computed tomography (CT) and 3D discrete element modeling (DEM). The nanofocus X-ray CT allows the visualization and characterization of the morphology and microstructure of sand particles during the particle fracture process. This information will be fully incorporated into the 3D DEM model of single sand particle fracture. Furthermore, a probabilistic approach which is based on the statistical law of single particle fracture and probability density function of particle contact force will be employed to predict particle breakage inside an oedometer specimen.This innovative research will unravel the nature of sand particle breakage by establishing a linkage between the breakage behavior and particle microstructure. Particularly, the role of intrinsic particle flaws in the fracture pattern (e.g., grain splitting or asperity breakage) and fracture strength behavior will be elucidated. This research will also establish a novel probability-based modeling approach for crushable sands.This proposal requests HK$1,495,960 (equivalent to US$192,154) to support a PhD student and a senior research assistant to conduct a three-year research on this topic. The outcome of this research will produce both scientific and engineering impacts. The former comes from an improved understanding of the fundamental behavior of crushable sands and its possible contribution to the research on other related breakable granular materials. The latter is mainly reflected in the enhanced ability of engineers to make improved design and construction of geotechnical systems in crushable soils. This is very relevant in Hong Kong where highly decomposed granite or volcanic soils exhibit distinct breakage characteristics.