A Modeling Method on Fractal Distribution of Cracks in Rocks Using Ae Monitoring

For underground mining and construction, it is important to obtain a discontinuities’ model of rocks for simulations to evaluate rock stability around the working space and fluid flow in these rocks. We have developed a method using the fractal property of acoustic emission (AE) source distribution to construct a feasible crack distribution model. We confirmed the usefulness of the model through laboratory experiments for granite specimens. The experiments demonstrated that the AE source distribution was fractal and that the relationship between amplitude and frequency of AE was fractal. Crack distributions in the specimen and on the surface were both fractal. Based on the results, 3-D crack distribution models were constructed using AE monitoring data obtained. This model describes the crack as a disk. The disk orientation was determined by a moment tensor analysis of AE waveforms. In this study, we applied the modeling method to uniaxial and triaxial compression tests on specimens of coal measures rocks (sandstone, siltstone and coal). Results showed that micro-cracking activity, which occurred prior to failure, differed depending on the rock type. We obtained characteristic models for each rock type. This technique was also applied to a micro-seismic data set obtained during mining at an underground Australian coal mine. The crack distribution model of roof rock on a longwall mining panel showed that most cracks were located in roof rock in front of the working face.