Abstract:

To study the fracture dynamic evolution process of grouting specimens under loading conditions, the graded gravel grouting specimen was periodically scanned during the uniaxial compression damage process using a CT scanning system. Based on the image reconstruction technique, the spatial visualization of the fracture structure inside the test grouting specimen block is achieved, and the structural characteristic parameters are characterized quantitatively such as the number and volume of fractures. The gray value and fractal dimension of the CT slices are calculated using Python programming to analyze the mesoscale damage extent at different loading stages of the grouting specimen. It is shown that the specimen’s internal fracture volume shows a trend of slow rise, slow fall, slow rise, and rapid rise. The fracture number shows a trend of increasing firstly and then decreasing during the whole compression stage. When the fracture expansion paths encounter gravel, most of the fractures expand around the gravel location and few fractures expand through the gravel. In addition, the fracture bifurcation expansion mostly appears at the interface between the cement matrix and gravel. The specimen damage process could be divided into four stages in terms of the fracture evolution process inside the specimen: initial defect expansion stage, internal crack compacting stage, fracture expansion stage, and fracture penetration stage. For the slice at the same loading stage of the test specimen, it is found that the value of the damage variable and fractal dimension shows a certain positive correlation, which is similar to the trends of the fracture volume evolution. The research results can provide a reference for the study of the failure process and fracture evolution law of the grouting body.

Key words: CT scan, grouting body, digital reconstruction, fracture evolution, quantitative characterization