{"title":"Asymmetric failure mechanisms of anisotropic shale under direct shear","authors":"","doi":"10.1016/j.ijrmms.2024.105941","DOIUrl":null,"url":null,"abstract":"<div><div>This study performed mechanical tests and monitored acoustic emissions (AE) in shale samples with six bedding layer orientations (<em>β</em> = 0°, 30°, 60°, 90°, 120°, and 150°) to investigate the progressive damage mechanisms under direct shear. The results revealed that the peak shear load (<em>P</em><sub><em>cr</em></sub>), crack initiation threshold (<em>P</em><sub><em>ci</em></sub>), crack damage threshold (<em>P</em><sub><em>cd</em></sub>), and cumulative AE count exhibited an approximate M-shaped trend as the bedding angle increased. The <em>P</em><sub><em>ci</em></sub>, <em>P</em><sub><em>cd</em></sub>, and <em>P</em><sub><em>cr</em></sub> values were minimal for shale specimens with <em>β</em> = 0°, <em>P</em><sub><em>cd</em></sub> and <em>P</em><sub><em>cr</em></sub> were maximal at <em>β</em> = 150° (followed by <em>β</em> = 60°), and <em>P</em><sub><em>ci</em></sub> reached the maximum at <em>β</em> = 60°. Thus, shale exhibits complex and asymmetric mechanical behavior under direct shear, a phenomenon seldom documented. The three-dimensional spatiotemporal evolution of the AE, evolution of <em>b</em>-values, peak frequency distribution, and the rise angle-average frequency (RA-AF) indicated that the microscale mechanism governing the asymmetric progressive failure of anisotropic shale under direct shear involved significant asymmetry in the formation type and scales of cracks. The AE characteristics of anisotropic shale were analyzed using multifractal theory. The width of the multifractal spectrum, Δ<em>θ</em>, accurately reflected the anisotropic characteristics of the AE time series. Moreover, the variation in the fractal dimension, Δ<em>f</em>, indicated that the different probabilities of microcracks with high AE energy are the fundamental cause of the shale's asymmetric failure.</div></div>","PeriodicalId":54941,"journal":{"name":"International Journal of Rock Mechanics and Mining Sciences","volume":null,"pages":null},"PeriodicalIF":7.0000,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"International Journal of Rock Mechanics and Mining Sciences","FirstCategoryId":"5","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S136516092400306X","RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"ENGINEERING, GEOLOGICAL","Score":null,"Total":0}
引用次数: 0
Abstract
This study performed mechanical tests and monitored acoustic emissions (AE) in shale samples with six bedding layer orientations (β = 0°, 30°, 60°, 90°, 120°, and 150°) to investigate the progressive damage mechanisms under direct shear. The results revealed that the peak shear load (Pcr), crack initiation threshold (Pci), crack damage threshold (Pcd), and cumulative AE count exhibited an approximate M-shaped trend as the bedding angle increased. The Pci, Pcd, and Pcr values were minimal for shale specimens with β = 0°, Pcd and Pcr were maximal at β = 150° (followed by β = 60°), and Pci reached the maximum at β = 60°. Thus, shale exhibits complex and asymmetric mechanical behavior under direct shear, a phenomenon seldom documented. The three-dimensional spatiotemporal evolution of the AE, evolution of b-values, peak frequency distribution, and the rise angle-average frequency (RA-AF) indicated that the microscale mechanism governing the asymmetric progressive failure of anisotropic shale under direct shear involved significant asymmetry in the formation type and scales of cracks. The AE characteristics of anisotropic shale were analyzed using multifractal theory. The width of the multifractal spectrum, Δθ, accurately reflected the anisotropic characteristics of the AE time series. Moreover, the variation in the fractal dimension, Δf, indicated that the different probabilities of microcracks with high AE energy are the fundamental cause of the shale's asymmetric failure.
期刊介绍:
The International Journal of Rock Mechanics and Mining Sciences focuses on original research, new developments, site measurements, and case studies within the fields of rock mechanics and rock engineering. Serving as an international platform, it showcases high-quality papers addressing rock mechanics and the application of its principles and techniques in mining and civil engineering projects situated on or within rock masses. These projects encompass a wide range, including slopes, open-pit mines, quarries, shafts, tunnels, caverns, underground mines, metro systems, dams, hydro-electric stations, geothermal energy, petroleum engineering, and radioactive waste disposal. The journal welcomes submissions on various topics, with particular interest in theoretical advancements, analytical and numerical methods, rock testing, site investigation, and case studies.