Modeling Method for Cracks in Rocks base on the Fractal Structure of the AE Source Distribution

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In underground construction it is important to obtain a discontinuities' model of rocks for simulations to evaluate rock stability around the working space and fluid in the rocks. In this study, three kinds of experiments were conducted to develop a more feasible modeling method of cracks in rocks based on AE (acoustic emission) monitoring data and the fractal properties of the AE source distribution.1.From hydrofracturing tests conducted on cubic-shaped rock specimens, it was found that the AE source distribution during increases in hydraulic pressure was fractal and that the relationship between amplitude and frequency of AE was also fractal. From analysis of the focal mechanisms of AE,it was possible to estimate the principal moment values, principal directions and crack types for events with a relatively large amplitude. However, it was difficult to determine the parameters of focal mechanism in most AE events.2.From fracture toughness tests using semi-circular disk specimens, it was shown that the 2-D crack and AE source distributions were both franctal. The fractal dimension of the lineaments extracted from a 2-D crack distribution image coincided with the dimension of a linear crack model obtained from AE monitoiring data.3.A 3-D crack distribution model was constructed using AE monitoring data obtained from uniaxial compression tests on prism-shaped specimens. In this model, the crack was described by a disk, and the fractal dimension of sectional lines that appeared on the surface of a specimen was adjusted to coincide with the dimension of lineaments extracted from a real crack image of the same surface of the specimen by correcting the AE parameters.It is thought that this new modeling method for cracks in rocks can be directly applied to field studies of underground construction in the future.