Evolution of tensile strength and cracking in granite containing prefabricated holes under high temperature and loading rate

Abstract

AbstractFor present applications in deep significant rock engineering, including underground repositories of high-level nuclear waste, an exhaustive comprehension of the impacts of high temperature and loading rate effects on the mechanical characteristics of granite emerges as an imperative necessity. Based on the Brazilian splitting test, Brazilian disc specimens with prefabricated holes were meticulously employed to guarantee the occurrence of radial compression failure. Combining microscopic experiments such as scanning electron microscopy and X-ray diffraction, the indirect tensile strength and damage mechanism of granite from the Yueyang area under the action of different temperatures and loading rates were thoroughly investigated. Furthermore, a nonlinear fitting equation between the two factors and tensile strength is suggested. At the same time, a simplified surface crack density based on pixel processing was defined. This allowed for a comparative assessment of how variations in temperature and loading rates induce varying degrees of macroscopic crack development and damage to the specimens. The findings suggest a direct proportionality between the tensile strength of granite and the loading rate, while an inverse proportionality is observed concerning temperature above 400 °C. However, a transient "gain effect" phenomenon manifests at temperatures below 400 °C. However, the impact of temperature on tensile strength is significantly greater than that of the loading rate, exhibiting a difference of approximately 8.7 times. Furthermore, the temperature is more prone to lead to the occurrence of secondary tensile cracks in specimens. The results of this research provide valuable guidance for ensuring the security of deep major rock engineering during construction.