The CT Experimental Research On The Rock Failure Process Under Uniaxial Compression Loading

For a long time, the rock failure process, as the basic content of rock mechanics study, has aroused extensive concern of the rock mechanics scholars and engineers, which in turn promotes the development of rock mechanics discipline. However, no matter the descriptions of the rock failure process based on the complete stress-strain curve, or the damage variables defined by the damage theory and the fracture mechanics established on the Griffith energy balance theory, can not explain the mesoscopic process and the basic mechanism of rock failure, in a widely-recognized way.This article carries out a series of experimental studies, to explore the rock failure process, and the development-evolution of the micro-rupture in the rock samples. We monitors the deformation-failure process of coal and rock sample under uniaxial compression loading, with the coordination of mini-uniaxial testing machine designed by ourselves, and the high-precision micro-CT system μCT225KVFCB of the CT laboratory. On the basis of lots of CT images from the experiment, we also analyze the meso-process of the rock sample deformation-failure, and the basic law of internal rupture evolution.Firstly, the article introduces the basic principle of CT technology, the high-precision micro-CT system μCT225KVFCB, the working principle and the configuration of the mini-uniaxial testing machine for coal and rock sample, and the conjunction method of the two apparatus above.Afterwards, we conduct a series of uniaxial compression tests of the coal, sandstone and cement-mortar specimens, to analyze the process and the law of different geo-materials. Using the micro-CT system, this study also carries out a real-time monitoring of the entire process of uniaxial compression tests for the coal samples and cement-mortar specimens. At meso-level, the deformation-failure processes and the basic laws of those coal samples and cement-mortar specimens are analyzed.During the micro-CT real-time monitoring of rock condition under uniaxial compression loading, there will be some error caused by the imprecise positioning of the CT scanner device. Aiming at this imperfection, a new image retrieval technology (IR for short, the same below) is proposed creatively. And the CT-IR technology is proposed specifically. With the similarity computing method based on the Manhattan distance measure, CT images of the same layer can be picked up from numerous CT images gained during the uniaxial compression tests. And the IR results are so reliable, that the author developed a computer program based on Vasiual Basic6.0language, achieving the automation of IR calculation process. The concept of IR technology provides a new idea for CT image processing. And, with the help of CT IR technology, analysis of micro-cracks distribution and evolution, based on the CT images of coal-rock specimens under uniaxial compression loading, can be carried out.Cross-sectional CT images of the cement-mortar specimens which are tested under uniaxial compression loading, are restructured through the CT processing program developed by our group. Moreover, at mesoscopic level, the basic law of coal and rock failure during the uniaxial compression test process gets further revealed.The concept of rupture based on the CT images, which is the percentage of the rupture pixels in a CT image, is put forward. And basing on this rupture concept, the variation of the rupture of the cement-mortar specimens during the uniaxial compression process, is analyzed statistically. The results show that most of the internal rupture structures of the cement-mortar specimens during its failure process, are initiated during the phase of yield deformation. And macroscopic ruptures have been generated basically before the residual strength stage.Through the analysis of a large number of CT images, it is discovered that the pore elements and the substance elements in the cement-mortar specimen CT images can be easily recognized when the CT threshold μ is in the range of0.025to0.035. Defining the background CT threshold, binarization for the CT images is implemented. Furthermore, with the help of those binarized CT images, some laws of the cement-mortar specimens’failure process are investigated.