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

在地下工程施工中，获得岩体的结构面模型对于模拟工作空间周围的岩体稳定性和岩体中的流体是非常重要的。本研究通过三种实验方法，探索一种更为可行的基于声发射的岩石裂纹模拟方法（声发射）监测数据和声发射源分布的分形特性。1.通过对岩石试件的水压致裂试验，结果表明，在水压升高过程中，声发射源的分布具有分形特征，声发射信号的幅值与频率之间存在着一定的关系，AE也是分形的。通过对声发射震源机制的分析，可以估计振幅较大的声发射事件的主矩值、主方向和裂纹类型。但在大多数声发射事件中，震源机制的参数很难确定。2.半圆形试件的断裂韧性试验结果表明，二维裂纹和声发射源的分布都是分形的。从二维裂纹分布图像中提取的分形维数与由声发射监测数据得到的线性裂纹模型的维数一致。3.利用棱柱体单轴压缩试验的声发射监测数据，建立了三维裂纹分布模型。在这个模型中，裂纹被描述为一个圆盘，通过对声发射参数的修正，调整试件表面剖面线的分形维数，使其与从同一表面真实的裂纹图像中提取的线性体维数相一致，认为这种新的岩石裂纹建模方法可直接应用于地下工程的现场研究，并可用于地下工程的现场研究未来

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.