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Progressive Transition from Extension Fracture to Shear Fracture of Altered Granite During Uniaxial Tensile Tests

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Abstract

A high degree of alteration causes swelling, disintegration and argillization of granite and thus weakens its physical and mechanical properties. Very few experimental studies, however, have been conducted to quantitatively characterize the strong-to-weak transition of the mechanical behaviours of granite affected by varying degrees of alteration. A new miniature tensile instrument system, which can visualize the failure process and simultaneously record the stress–strain curves, was utilized to test the tensile strength of dog-bone sliced samples of altered granite. Meanwhile, an improved quantitative method was proposed to characterize the alteration degree. The results demonstrate that the tensile strength of granite decreases significantly with increasing alteration rate, while the strain at the peak strength and fracture angle increase. Additionally, the orientation of weaker crystals and the mineral size distribution significantly affect fracture propagation. But the effect will be weakened as the alteration rate increases. On the basis of fracture angle, tensile peak strength, strain at peak strength, and microscopy images of crack initiation and propagation, three major classes of fractures are identified from the test results: (1) extension fracture at a low alteration rate: crack initiates and propagates along biotite-brittle mineral interfaces; (2) shear fracture at a high alteration rate: intragranular crack initiates within altered feldspar and propagates along the interior of altered mineral grains; (3) hybrid fracture at a moderate alteration rate: the above two failure phenomena coexist. A simple model that considers the fracture process of altered granite was proposed to explain the transition from extension fracture to shear fracture.

Highlights

  • A new visual miniature tensile instrument is utilized to capture the crack initiation and propagation.

  • An improved quantitative method is proposed to characterize the alteration degree of granite.

  • As alteration degree increases, the tensile strength of granite significantly decreases, whereas both the strain and the fracture angle increase.

  • The transition from extension fracture to shear fracture of altered granite is detected.

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modified from found in Martin and Chandler (1994)

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Funding

This research is supported by the Second Tibetan Plateau Scientific Expedition and Research (STEP) program (Grant No. 2019QZKK0904), the National Natural Science Foundation of China (Grant No. 41941019) and the National Key R&D Program of China (Grant No. 2019YFC1520601).

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Contributions

SL performed the data analyses and wrote the manuscript; HL contributed to the conception of the study; CDM contributed significantly to analysis.

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Correspondence to Hengxing Lan.

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There is no competing interest. We declare that the authors have no competing interests as defined by Rock Mechanics and Rock Engineering, or other interests that might be perceived to influence the results and/or discussion reported in this paper.

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Liu, S., Lan, H. & Martin, C.D. Progressive Transition from Extension Fracture to Shear Fracture of Altered Granite During Uniaxial Tensile Tests. Rock Mech Rock Eng 55, 5355–5375 (2022). https://doi.org/10.1007/s00603-022-02897-6

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  • DOI: https://doi.org/10.1007/s00603-022-02897-6

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