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

在地下工程中，获得岩体的不连续面模型以模拟评价工作空间周围岩石的稳定性和岩石中的流体是非常重要的。本研究基于声发射监测数据和声发射源分布的分形特性，开展了三种实验，建立了一种更为可行的岩石裂缝建模方法。通过对立方岩样进行水力压裂试验，发现水力压力增大时声发射源的分布呈分形，声发射振幅与频率的关系也呈分形。通过对声发射震源机制的分析，可以估计出振幅较大的事件的主矩值、主方向和裂缝类型。然而，大多数声发射事件的震源机制参数难以确定。采用半圆形圆盘试样进行断裂韧性测试，结果表明二维裂纹分布和声发射源分布均为分形分布。从二维裂纹分布图像中提取的线形维数与从声发射监测数据中获得的线形裂纹模型的维数相吻合。利用棱镜形试件单轴压缩声发射监测数据，建立了三维裂纹分布模型。在该模型中，裂纹用圆盘来描述，通过修正声发射参数，调整试样表面出现的断面线的分形维数，使其与试样同一表面真实裂纹图像中提取的线形维数一致。认为这种新的岩石裂缝建模方法可直接应用于地下工程的现场研究。

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.