| The microstructure of sedimentary rocks is a complex assembly of distinct elements, including varying sized crystals, grains, cementing material and void space. Current continuum mechanical treatments of failure are not adequate to fully describe fracture and damage processes on the microstructure level because at this scale no true "continuum" exists. The research described within this dissertation treats the physics of rock failure with a non-continuum approach. A numerical, discrete element procedure is developed and applied to model the process of microfracture in porous sedimentary rock in two dimensions. Basic mechanics principles are applied to the microstructural constituents of the rock to simulate physical behavior and failure of the material.; No numerical procedure can be considered valid unless it is based on sound physical observations and principles, and unless it can reasonably reproduce physical data under simple experimental conditions. For this reason, the research presented in this dissertation includes three important stages: physical observation, numerical model development, and model verification and improvement based on experimented data.; A review is presented of sedimentary rock formation processes and microstructure. Experimental research on the failure of sandstone and limestone samples are described, along with details of fracture surface microscopic observations. A discrete element approach is used to model this observed structure and simulate development of microfractures under simple load conditions. Numerical and graphical illustrations are presented for samples subjected to tension, uniaxial compression, and biaxial compression loading. Simulation results compare favorably with experimental observations, including the predicted load-deformation behavior, microcrack type and orientation, and eventual macroscopic failure mode. |
