Abstract
Meso-crack evolution mechanism of shale is a key factor affecting the mechanical properties of shale. In order to explore evolution laws of cracks in shale during loading, a meso-crack monitoring system, loading test equipment and an automatic ultrasonic data acquisition system were set up. On this basis, a set of experimental apparatus simultaneous monitoring multi-parameters of shale micro-crack was designed, and destruction experiments of shale samples with different bedding angles were carried out to find out evolution characteristics of cracks. The results show the following: (1) The designed apparatus can monitor ultrasonic, mechanical and video information simultaneously of crack evolution in the entire process of shale destruction under load to provide information for analyzing acoustic and mechanical characteristic responses of crack propagation at key time nodes. (2) With an increase in load, shale will undergo four stages of destruction: crack initiation, propagation, penetration and overall failure. In the course of these stages, acoustic characteristics and mechanical characteristics are in good agreement, which proves the validity of predicting rock mechanical parameters with acoustic data. (3) During the loading process of shale, the main amplitude of acoustic wave is more sensitive than mechanical parameters to the change of rock cracks. Research results have important theoretical reference value for evaluating wall stability of shale gas horizontal well with ultrasonic data.
Highlights
Mechanisms of rock deformation and failure and prediction of rock failure have always been key contents in geotechnical engineering
We have developed an integrated unit and system for monitorand sounds system of ultrasonic monitoring of mesoscopic fissures during ing and pictures wave during propagation of mesoscopic fissures in shale shale destruction
The image segmentation method based on porosity was adopted in the binarization process of the shale fracture in this study
Summary
Mechanisms of rock deformation and failure and prediction of rock failure have always been key contents in geotechnical engineering. Many research studies have been conducted in two aspects. One aspect is monitoring crack evolution during rock failure. Xu. Jiang et al [1] observed evolution laws of cracks in coal sample during shear destruction with a mesoscopic monitoring device developed by themselves. Described the shape and propagation of cracks during rock destruction by CT scanning. Liu Dongmei et al [3] accounted for the process of fracture initiation, growth and close in rock with a camera and image processing technology. Zhao Cheng et al [4] examined deformation and destruction features of rock with pre-fabricated single cracks under uniaxial compression with image analysis and digital image technology developed by themselves
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