The mechanical behaviour of pre-existing transverse cracks in lignite under uniaxial compression
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ORIGINAL ARTICLE
The mechanical behaviour of pre-existing transverse cracks in lignite under uniaxial compression Jianhua Wen . Zhan Tang . Ashley P. Dyson . Ali Tolooiyan
Received: 14 September 2020 / Accepted: 16 November 2020 Ó Springer Nature Switzerland AG 2020
Abstract Intermediate geotechnical materials such as Victorian Brown Coal (VBC) often exhibit complex fracture characteristics due to the interplay of ductile and brittle behaviour. A diverse set of in situ joint orientations and fracture characteristics are found in the open-cut mines of the Latrobe Valley, Victoria, Australia. As such, the propagation of pre-existing discontinuities plays a significant role in the potential failure mechanisms of open-cut mines in the region. Although field assessment has yielded a range of Victorian Brown Coal in situ joint characteristics, insufficient data exists to determine the relationship
J. Wen Civil Engineering Department, College of Water Conservancy and Civil Engineering, South China Agriculture University, Guangzhou 510642, China e-mail: [email protected] Z. Tang Civiltest Pty Ltd, 10 Latham Street, Mornington, VIC 3931, Australia e-mail: [email protected] A. P. Dyson Geotechnical and Hydrogeological Engineering Research Group (GHERG), Federation University Australia, Northways Rd, Churchill, VIC 3844, Australia e-mail: [email protected] A. Tolooiyan (&) School of Engineering, University of Tasmania, Hobart, TAS 7001, Australia e-mail: [email protected]; [email protected]
between the fracture orientation of VBC and joint compressive strength. To supplement available site investigation data, experimental results of uniaxial compressive tests on pre-fractured Victorian Brown Coal specimens performed under laboratory conditions are presented for various crack angles to determine the relationship between fracture angle and joint compressive strength. Fractured VBC is found to exhibit a reduced uniaxial compressive strength, with appreciably varied fracture propagation characteristics depending on the fracture initiation angle. Laboratory tests were conducted on soaked VBC specimens containing predefined cracks (for angles of 0°, 15°, 30°, 45° and 60° to the axis of symmetry) as well as intact coal specimens, with fracture propagation paths photographed along the specimen surface. Intact coal specimens under compression experienced brittle failure with crack propagation parallel to the direction of loading. For specimens with pre-existing fractures, the crack angle was observed to significantly affect the failure mode and the direction of crack propagation. Obtained results suggest pre-existing crack angles alter the shape of the stress–strain curve, with a range of unconfined compressive strengths and crack initiation strengths presented. It was noted that pre-existing crack angles of 45° yielded the minimum observed failure stress. Given the presence of desiccation cracks, micro-cracks and large-scale jointing within Victorian Brown Coal, compressive strength
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