Characterization and evaluation of brittleness of deep bedded sandstone from the perspective of the whole life-cycle evolution process

The quantitative determination and evaluation of rock brittleness are crucial for the estimation of exca-vation efficiency and the improvement of hydraulic fracturing efficiency. Therefore, a "three-stage" triax-ial loading and unloading stress path is designed and proposed. Subsequently, six brittleness indices are selected. In addition, the evolution characteristics of the six brittleness indices selected are characterized based on the bedding effect and the effect of confining pressure. Then, the entropy weight method (EWM) is introduced to assign weight to the six brittleness indices, and the comprehensive brittleness index Bc is defined and evaluated. Next, the new brittleness classification standard is determined, and the brittleness differences between the two stress paths are quantified. Finally, compared with the previous evaluation methods, the rationality of the proposed comprehensive brittleness index Bc is also verified. These results indicate that the proposed brittleness index Bc can reflect the brittle characteristics of deep bedded sand-stone from the perspective of the whole life-cycle evolution process. Accordingly, the method proposed seems to offer reliable evaluations of the brittleness of deep bedded sandstone in deep engineering prac-tices, although further validation is necessary.(c) 2023 Published by Elsevier B.V. on behalf of China University of Mining & Technology. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).