基于<bold>CT</bold>成像和数字体图像相关法的岩石内部变形场量测方法的研究进展

Abstract

<p indent="0mm">Rock mechanics plays a critical role in mining engineering, slope engineering, tunnel engineering, water conservancy, hydropower engineering, and some newly developing rock mass engineering, such as deeply buried oil and gas storage, underground nuclear waste repository, geothermal development, etc. The evolution of the internal discontinuous structure of rock under the coupling of multiple physical fields such as stress field, seepage field, and temperature field is an important research topic in the field of rock mechanics. Scholars have investigated the internal structure characteristics and their evolution process at different scales with various equipment. High-resolution microtomography (Micro CT) with micron or even nanoscale resolution has been widely used in internal structure detection, digital core modeling, and numerical modeling of rock. The digital volume correlation (DVC) method can quantitatively analyze and visualize the internal 3D deformation field of rock, and its combination with Micro CT provides a new method for transparent analysis and deduction of discontinuous structures and multi-physical fields in rocks. This paper systematically reviews the research on internal deformation measurement of rocks by using Micro CT and DVC in terms of <italic>in-situ</italic> loading device with Micro CT, the theory of DVC, the influence of micro/meso-structures in rocks, and experimental measurements. To view the internal structures of rocks under different physical fields, various <italic>in-situ</italic> loading devices combined with Micro CT were developed, e.g., uniaxial loading device, triaxial loading coupled with seepage device, gas adsorption device, and heating device. In these devices, factors such as the strength of rock, physical field, material strength of chamber, X-ray energy and penetration, real-time performance of image acquisition, and quality of reconstructed images should be comprehensively considered. By using <italic>in-situ</italic> loading devices and Micro CT, a series of volume images of rocks are obtained before and after deformation, and then DVC is adopted to calculate the three-dimensional deformation field by analyzing the correlation between these volume images. According to the registration algorithms, DVC can be categorized into local DVC (L-DVC) and global DVC (G-DVC). The basic principle and development of DVC are reviewed. Due to the limitation of the heterogeneity of rocks and the accuracy of the image acquisition equipment, natural micro structures in rocks do not have ideal speckle patterns, which affects the accuracy of DVC. It is indicated that the larger the average gray gradient and Shannon entropy and the smaller the structural variation coefficient of a rock image, the higher the accuracy of DVC. The accuracy of G-DVC is slightly better than that of L-DVC, but its calculation efficiency is lower, especially when the mesh size is small. The applications of DVC for investigating strain localization in rocks, measuring carbon dioxide-induced strain in coal, and oil shale pyrolysis are presented. Despite some impressive achievements, DVC is still faced with some core challenges, e.g., the low accuracy of the DVC algorithm and artifact error correction, the influence of the microstructures in rocks, parameter identification and numerical model verification of rocks, and deformation field measurement under the coupling of multiple physical fields. With the popularization of Micro-CT in laboratories, DVC will be further applied to measuring the three-dimensional deformation field in rocks.