基于光反射率突变的受力岩石裂纹提取方法

Method for extracting stressed rock crack based on light reflectivity mutation

裂纹识别与提取是认识围岩裂纹演变规律的基础。针对目前基于可见光照片的受力岩石裂纹提取方法对由多色矿物组成的复杂岩石(如花岗岩)裂纹提取效果较差的问题,提出一种基于光反射率突变的受力岩石裂纹提取方法。该方法包括光反射率计算、光反射率突变点识别、光反射率突变点空间分异性分析、裂纹信息提取4个关键步骤。裂纹发育引起的光反射率突变点在空间上的分异性是识别裂纹的关键特征,因此,引入反映空间点分布集中程度的指标−分异系数C,根据光反射率突变点的空间分异性判断数字图像中是否存在裂纹。判断出数字照片中存在裂纹后,一方面,通过光反射率变化速率反映裂纹活动的瞬时信息,以研究试件在何时、何处有裂纹产生或扩展;另一方面,提取出裂纹活动的累积信息,以分析一段时间内岩石表面裂纹的发育、扩展情况及贯通程度。实验结果表明:①受力岩石裂纹发育、扩展可引起光反射率突变,突变速率可达0.2/s,远大于由其他随机因素导致的变化速率(0.03/s)。②在裂纹活动时刻,光反射率突变点呈显著的空间分异现象(C值可达189),分异系数远大于随机分布时的值(C值为1)。③所提方法能够提取出裂纹活动的瞬时信息和累积信息。最后讨论了岩石破裂过程中光反射率变化的原因、所提方法的岩石力学意义及其在巷道安全巡检中的应用前景。

The crack identification and extraction is the basis of understanding the evolution law of surrounding rock cracks.The existing methods for extracting stressed rock cracks based on visible light photos are poor in extracting the cracks of complex rocks(such as granite)composed of polychromatic minerals.In order to solve the problem,a method for extracting stressed rock cracks based on light reflectivity mutation is proposed.The method comprises four key steps of light reflectivity calculation,light reflectivity mutation point identification,light reflectivity mutation point space heterogeneity analysis and crack information extraction.The spatial differentiation of the mutation points of light reflectivity caused by crack growth is the key characteristic of crack identification.Therefore,the index-differentiation coefficient C,which reflects the concentration degree of spatial point distribution,is introduced.It is used to judge whether there is a crack in the digital image according to the spatial differentiation of the mutation points of light reflectivity.After the crack in the digital photo is judged,on one hand,the instantaneous information of the crack activity is reflected through the change speed of the light reflectivity,so as to study when and where cracks occur or expand in the specimen.On the other hand,the cumulative information of crack activity is extracted to analyze the development,propagation and penetration degree of rock surface cracks over a period of time.The experimental result shows that:①The development and propagation of stress cracks in rock can cause the mutation of light reflectivity.The mutation speed can reach 0.2/s,which is much larger than the change speed(0.03/s)caused by other random factors.②At the crack active time,the mutation point of light reflectance shows significant spatial differentiation(C value can reach 189),and the differentiation coefficient is much larger than that in random distribution(C value is 1).③The proposed method can extract the instantaneous information and cumulative information of crack activity.Finally,the reason for the change of light reflectivity during rock crack,the significance of rock mechanics of the proposed method and its application prospect in roadway safety inspection are discussed.