| Summary: | 博士 === 國立臺灣大學 === 土木工程學研究所 === 96 === Macroscopic mechanical properties of, such as uniaxial compressive strength and Young’s modulus were found to be significantly affected by their petrographic properties, e.g. the porosity n and the grain area ration GAR. The intricate relationship between the macroscopic properties of sandstones and their petrographic or microscopic properties necessitates further study in exploring how the microscopic properties influence the macroscopic mechanical behavior.
In this research, numerical analyses based on the bonded-particle model (BPM), the microscopic properties of which originated from the bonded strength and stiffness, were thus conducted as a systematic study aiming at unraveling these microscopic mechanisms. A series of tests was conducted, and the results were compared with the actual behavior of sandstone. A numerical model comprised of three types of particles, grain particles GP, matrix particles MP and porous matrix particles PP, was accordingly proposed to represent the sandstone.
The results of analyses demonstrated how the petrographic parameter GAR and porosity n determined the proportions and the numbers of GP, MP and PP. The strength and stiffness of these bonds were estimated based on back-analyses. Accordingly, the results of parametric study indicate that matrix particles tend to have stronger bonding strength yet softer stiffness, when compared to the grain particles.
On the other hand, since a conventional petrographic analysis does not allow a systematic and detailed study on how the microscopic factors affect the macroscopic behavior of inter-layered rocks, this research adopted the bonded particle model to explore the micro-mechanisms associated with the strength and stiffness of inter-layered rocks. The model was first calibrated by comparing the simulations to the actual behavior until they tally with each other. Following, the microscopic factors, including the bond strength, the bond stiffness, type of bonds and friction of particles and type of bond stiffness, are varied to study their influences. As expected, the bond strength and the bond stiffness are found to have a direct and significant influence on the macroscopic uniaxial compressive strength and stiffness, respectively. Furthermore, close observations on the breaking of bonds during the loading process reveal interesting phenomena, including the transition of shear/normal bond breaking, the type of internal fracture and the factors controlling internal failure, etc. These phenomena enlighten the interpretations about the micro-mechanisms accounting for the macroscopic strength and stiffness of inter-layered rocks.
|
|---|
