Effect of Open-Fire-Induced Damage on Brazilian Tensile Strength and Microstructure of Granite

Abstract

Deformation and stability of surrounding rock of a tunnel could be significantly affected by the fire accident-induced open-fire damage. In this study, the influence of open-fire damage on the P-wave velocity, Brazilian tensile strength (BTS), and the associated microstructure evolution of granite is investigated. The open-fire damage is generated by heating the rock sample with charcoal fire for 3 h prior to the subsequent tests. P-wave velocity of intact and heated specimens is measured. The microstructure of specimens with different distances to the open fire is observed utilizing a polarizing microscopy. Brazilian splitting tests on the heated specimens are then conducted combined with high-speed camera for monitoring the failure process. Both P-wave velocity and BTS are found to increase rapidly as the distance from the specimen to the open fire increases. When the distance between the specimen and the open fire is larger than 125 mm, the values of P-wave velocity and BTS tend to level off at the values of unheated specimen. The degradation of P-wave velocity and BTS with increasing open-fire damage is mainly attributed to the induced microcracks in the process of approaching the open fire. The trans-granular microcracking is found to be an effective indicator to evaluate the degree of open-fire damage. Two negative exponential models are proposed for the variation of the P-wave velocity and BTS with the damage distance from the specimen to the open fire. The proposed model is validated by the reasonable agreement between model predictions and experimental results.