報 告 人：David Potyondy
報告時間：11 月 4日 14:30
報告地點：明志樓A536
報告人簡介：David Potyondy is a Senior Geomechanics Engineer at Itasca Consulting Group, Minneapolis, with extensive expertise in computational structural mechanics, rock mechanics, fracture mechanics, and both continuum and discontinuum numerical methods. His work is particularly renowned for advancements in discrete element methods (DEM), including bonded-particle modeling, which simulates the fracture and damage processes in rocks and other brittle materials. Additionally, he worked on important geomechanical projects like Geogrid Reinforced Pavement Design, the Thermal-Mechanical Stability Study for rock mass behavior around underground openings, and tunnel stability studies related to the Yucca Mountain nuclear waste repository. Dr. Potyondy obtained his Ph.D. in 1993 in Civil Engineering from Cornell University and was an Assistant Professor in the Department of Civil Engineering at the University of Toronto during the 2004–2005 academic year. His research focuses on rock mechanics, fracture mechanics, and the development of numerical models for simulating the behavior of geological materials under stress. He is also deeply involved in developing software tools such as Particle Flow Code (PFC) for geomechanical simulations, with applications in understanding excavation stability, long-term rock mass behavior, and fracture propagation in both civil engineering and geological contexts.
報告內容摘要：The aim of this report is to explore the potential application of the combined particle model (BPM) in simulating the rock disintegration process in the vicinity of wellbore shot holes in sandstones. The study constructed a two-dimensional BPM model based on the Castle Gate Sandstone, on the basis of which the influence of boundary conditions around wellbore shot holes in dry sandstones on the surface debris formation behavior was analyzed. A variety of macroscopic responses, including direct tensile strength and unconfined compressive strength, as well as a variety of mechanisms in direct tensile and compression tests were successfully reproduced by the constructed synthetic material model. In addition, the main mechanisms of the type of rupture damage produced by synthetics in thick-walled cylinder (TWC) tests have been reproduced. This mechanism, named “buckling-assisted fragmentation”, is characterized by the formation of thin rock fragments resembling onion skins by the processes of flexure and exfoliation, leading to rupture damage. The results show that the perforation collapse behavior of the synthetic material is closely related to the borehole resolution (defined as the number of particles on the borehole diameter), and the TWC intensity decreases as the borehole resolution increases. This finding suggests that the strength of the perforation decreases with the increase of the perforation size. In order to more accurately simulate the physical behavior of sandstone, this study further proposes an improved scheme for two-dimensional planar connection materials, including reducing the particle connectivity of the current dense microstructure, and increasing porosity by introducing initial cracks and gaps. It is expected that these adjustments will result in a better match between the axial stress-strain curve of the material under triaxial compression and the loading curve in the TWC test during the initial hardening phase.
主辦單位：土木工程與測繪學院
科學技術發展研究院
