Distinct Element Analysis for Rock Failure under Uniaxial Compression

In order to better understand the mechanics of fracture propagation in rock, we have developed an analysis program based on the concept of the DEM (Distinct Element Method) and simulated a uniaxial compression test. Even at present, it is still difficult to measure all AE (Acoustic Emission) events generated during an experiment due to the limit of recording speed of a measuring device, and the influence of the noise. On the other hand, the DEM can simulate realistic, appropriate rock fracturing process, and makes it possible to consider generation of all microcracks including those difficulties in an AE measurement. Our simulation results are well in agreement with the fracturing process deduced from AE measurements in the previous laboratory experiments conducted by the other researchers. Moreover, they provide the new findings to solve the disagreement; the conventional theories and microscopic observations suggest that tensile cracks cause AE events, whereas an abundance of shear type AE events are observed in the experiments. Our simulation results indicate that the energy released from a tensile crack is very small compared with that from a shear crack, due to the tensile strength much smaller than compressive strength. Since it is thought that such a small AE is easily buried in a noise and hard to be measured in an experiment, shear AE would be observed dominantly in an actual AE monitoring experiment. These results, including the new finding to solve the conflict, indicate that DEM is an effective numerical analysis technique for studying the dynamics of microcracking in brittle materials like rock