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Mechanical properties and failure patterns of migmatized gneiss with metamorphic foliation under UCS test

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    0511743 - ÚGN 2020 RIV AT eng J - Journal Article
    Berčáková, Andrea - Melichar, R. - Souček, Kamil
    Mechanical properties and failure patterns of migmatized gneiss with metamorphic foliation under UCS test.
    Rock Mechanics and Rock Engineering. Roč. 53, č. 4 (2020), s. 2007-2013. ISSN 0723-2632. E-ISSN 1434-453X
    R&D Projects: GA MŠMT(CZ) LO1406
    Institutional support: RVO:68145535
    Keywords : mechanical anisotropy * metamorphic foliation * shear fracture * tensile fracture * uniaxial compressive strength
    OECD category: Mechanical engineering
    Impact factor: 6.730, year: 2020
    Method of publishing: Limited access

    Preferentially oriented, primary structures within the rock matrix such as schistosity, foliation, lamination and/or cleavage are responsible for anisotropic behaviour in rocks (Singh et al. 1989, Ramamurthy 1993, Nasseri et al. 2003, Esamaldeen et al. 2014). For rocks with an anisotropic structure, their mechanical, hydraulic and/or seismic properties change and vary with different directions of loading (Agliardi et al. 2014). The irregular structure can also change the failure mode of the intact rock and influence secondary crack propagation. The mechanical behaviour of anisotropic rocks including the strength and deformation properties, as well as failure patterns of the rocks, has been studied by many researchers (Ramamurthy 1993, Nasseri et al. 2003, Ghazvinian et al. 2012, Basu et al. 2013, Esamaldeen et al. 2014, Plinninger and Alber 2015, Singh et al. 2015, Usol’tseva et al. 2017, Yin and Yang 2018). Knowledge of the mechanical properties and failure mechanism of the rocks are required in underground engineering analyses based on rock mechanics as well as rock slope stability problems. For example, slope design in open pit mines must be conducted considering the orientation of the schistosity fabric of the rock. Also, the stability of the walls in open pit mines can be reduced in case of unfavourable orientation of the planes of weakness compared to the attitude of the slope.Metamorphic rocks with preferentially iso-oriented parallel structures of long or flat minerals (i.e. foliation), should be considered as being transversally isotropic rocks that have a direction-dependent strength (Goodman 1989). The foliation planes are planes of weakness within the rock fabric that are responsible for different strength and deformation properties in relation to the occurring stress state.The anisotropic strength behaviour of the rocks can be characterised according to the classification suggested by Ramamurthy (1993). He distinguished three different curves of strength anisotropy, called “wavy shaped”, “U-shaped” and “shoulder shaped” anisotropy. The curves show a relation between the values of the uniaxial compressive strength UCS [MPa] and the anisotropy angle α [°] as illustrated in Fig. 1. The anisotropy angle represents the angle between the planes of weakness and the loading direction.The Young’s modulus, i.e. the modulus of elasticity E[GPa] is one of the most important parameters that characterise the elastic deformability of rocks. The anisotropic deformation behaviour of rocks can be characterised accord-ing to Nasseri et al. (2003). They specified and named two different types of curves of modulus anisotropy: “U-shaped” and “decreasing order-shaped” curves. The curves reflect the relationship between the values of the Young’s modulus E[GPa] and the anisotropy angle α [°].The failure mechanism of intact rock is commonly determined by a macroscopic description of the fractures affecting the failed rock specimens. In general, three different types of rock failure can occur: anisotropic extension, shear failure and isotropic tensile failure (Blès and Fuega 1986).The purpose of the present paper is to characterise the failure mechanisms of migmatized gneiss with metamorphic foliation and to discuss the importance of the effect that the orientation of the planes of weakness has on the failure of the tested rock.
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