基于图像分析的节理岩体单轴压缩损伤演化研究

DAMAGE EVOLUTION OF JOINTED ROCK MASSES UNDER UNIAXIAL COMPRESSION BASED ON DIGITAL IMAGE ANALYSIS

为定量地研究节理岩体的损伤演化规律,对岩体石膏模型试件单轴压缩试验过程中拍摄的表面数字图像进行处理分析。编制Matlab程序,实现单个裂纹的识别、裂纹长度和方位角、总裂纹面积分数和总裂纹分形维数的计算。对节理倾角和节理连通率这2个参数组合变化下的试件表面裂纹图像的分析结果为:(1)试件表面总裂纹面积分数和总裂纹分形维数变化规律基本相似,在各节理连通率和各节理倾角下,2个参量都随轴向应变的增加而增大;(2)可将试件分为两大组,节理倾角为0°,15°,75°,90°试件(劈裂破坏为主)和节理倾角为30°,45°,60°的试件(剪切破坏为主),第1组试件表面的总裂纹面积分数和总裂纹分形维数值都高于第2组试件;(3)具有相同节理连通率的试件,在试验开始点不同节理倾角的总裂纹面积分数基本相同,在峰值荷载点和试验结束点的总裂纹面积分数随节理倾角的变化曲线基本呈V型(最小值在节理倾角为45°处,最大值在节理倾角为0°处);(4)表面裂纹在试验开始时和加载过程中的各向异性分布特征,可以用裂纹面积分数沿裂纹方位角的分布图来表征。研究结果表明,表面裂纹图像分析可以有效地定量研究节理岩体试件的各向异性损伤演化特征。

The digital images of the surface of jointed gypsum samples under uniaxial compression were analyzed in order to study the damage evolution of jointed rock mass quantitatively. A computing program was developed with Matlab for the identification of individual crack and the calculations of the length and orientation of cracks, the fractions of total crack area and the total fractal dimensions of cracks. The results of the digital images considering the inclination angles and continuity rates of joints were analyzed. Both the fractions of total crack area and the total fractal dimensions of cracks increased with the increasing of axial strain in similar tendency. The specimens were classified into two groups according to the orientation angles of joints. The specimens with angles of 0°, 15°, 75 ° and 90° were assigned in the first group（the main failure mode is axial splitting）, and the ones with angles of 30°, 45 ° and 60° in the second group（the main failure mode is shear sliding）. The fractions of total crack area and the total fractal dimensions of cracks of the first group are larger than those of the second group. When the continuity factors of joints were the same, the fractions of total crack area of the specimens with different orientation angles of joint were largely the same at the beginning of tests; while the curves of the fractions of total crack area vs. the orientation angles of joint were V-shaped at the peak load and at the end of test （the maximum and the minimum values were for specimens with the orientation angles of joint of 0° and 45° respectively）. The anisotropic characteristic of surface cracks of the jointed specimens at the beginning of test or during the loading can be represented by the distribution of fractions of crack area along the crack orientations. The study showed that the anisotropic damage evolution of jointed specimens was efficiently captured with the method of image analysis.