Investigating the Evolution of Rock Discontinuity Asperity Degradation and Void Space Morphology under Direct Shear

Rock mass discontinuities represent planes of relative weakness and enhanced hydraulic conductivity and, thus, have a substantial influence on the hydro-mechanical behaviour of the overall rock mass. While the shearing of rock mass discontinuities has been extensively studied in the past, there remains uncertainty surrounding the mechanisms by which surface asperities deform and degrade during shear and how this degradation influences the aperture distribution. Although prior studies have attempted to investigate asperity failure mechanisms, they have been hampered by the lack of appropriate visualization and modelling tools. In particular, until recently it was not possible to observe asperity damage without physically separating the joint specimen or explicitly modelling the development of damage during a direct shear test.In the last decade, X-ray Computed Tomography (CT) has emerged as an ideal tool to nondestructively characterize fractures and damage in geomaterials. Over this same period, hybrid continuum/discontiuum modelling techniques, capable of explicitly modelling fracture and fragmentation have been developed and applied to rock mechanics problems. However, to date, there has been limited application of these technologies to the study of rock discontinuities subjected to shearing. The overall goal set forth in this thesis was to combine the use of these two technologies to develop an improved understanding and confirm empirical assumptions regarding the evolution of asperity degradation and fracture geometry as a result of shearing.The adopted experimental approach involved creating a series of replicated discontinuity specimens that were then subjected to varying shear displacements under different normal loading conditions. Subsequently, micro-CT imagery of the specimens was acquired and an image processing and analysis procedure was developed to quantitatively evaluate changes in asperity damage and fracture geometry as a function of shear displacement and applied normal load.Through the use of hybrid Finite-Discrete element (FEM-DEM) modelling, the experimentally observed shearing process was then recreated numerically to glean further insight into the shearing process and the different mechanisms involved. To do so, a new calibration procedure was first developed to systematically establish suitable input parameters. Lastly, the application of FEM-DEM to problems involving larger-scale discontinuity shearing, where physical testing would be difficult or unfeasible, was investigated.

Department dc:contributor.department

Civil Engineering

Year dc:date.issued

2014

Author dc:creator

• Tatone, Bryan Stanley Anthony

Advisor dc:contributor.advisor

• Grasselli, Giovanni

• Asperity damage
• Direct shear test
• Discontinuity
• FEM-DEM
• Fracture aperture
• Micro-CT

Handle dc:identifier.uri

http://hdl.handle.net/1807/68345

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/68345