| Localization and failure of rock under plane-strain conditions are important concerns in geotechnical engineering. For example, the assumed failure mechanism affects the prediction of maximum loads that could be applied to man-made and natural structures composed of rock, such as embankments, earth dams and slopes. However, there are few experimental data available on rock under plane-strain loading. Furthermore, post-failure and shear-band characteristics of rock under plane-strain conditions have not been studied yet.; A series of plane-strain tests have been performed on Berea sandstone and Wildmoor sandstone, relatively hard and soft rocks. Two types of failure phenomena have been observed. A single plane called a shear band formed in the soft rock, which exhibited pronounced non-linear behavior, while the hard rock, which showed very little non-linear behavior prior to peak load, failed by a planar feature with a kink. The main purpose of this study was to theoretically analyze the observed features from a plasticity and a fracture mechanics point of view.; The formation and orientation of localization in the soft sandstone was studied theoretically within the framework of equilibrium bifurcation theory. First, an elastic plastic constitutive model with non-linear yield and potential functions was developed from the experiments. The orientation of the shear band and the bifurcation point were predicted from two types of shear banding bifurcation theories, and compared with the experimental results. Furthermore, for the purpose of solving boundary value problems, the developed constitutive model has been implemented into the software FLAC, and validated against the experimental results. Fracture mechanics was used to analyze the kinked failure plane. In this approach, the failure plane was viewed as shear crack propagation.; In the experimental effort, the acoustic emission (AE) method was used to monitor failure of the materials. From the experimental evidence and AE locations, it was observed that the failure plane fully forms after peak load. To further study the failure plane characteristics, the quantitative acoustic emission method was applied to identify the micromechanisms of the failure process. |
