Fracture Behaviour of Two Microstructurally Different Rocks Exposed to High Static Stress and Cyclic Disturbances: Fid-Bau Portal

Fracture Behaviour of Two Microstructurally Different Rocks Exposed to High Static Stress and Cyclic Disturbances

Miao, Shuting / Pan, Peng-Zhi / Yu, Peiyang / Hou, Wenbo

Abstract The mechanical behavior of rocks under cyclic loading has been widely studied, while the effect of microstructure on the dynamic responses of rocks was not well clarified. A series of uniaxial monotonic and coupled static–dynamic tests were performed on two microstructurally different rocks, i.e. red sandstone and granite, with the combination of digital image correlation (DIC) and acoustic emission (AE) techniques. Experimental results revealed that dynamic disturbances have a large role in the damage evolution and fracturing mechanism of rocks. A two- or three-stage evolution trend is observed in the variations of axial strain and cumulative AE counts during cyclic disturbances. The microstructure within rocks significantly affects the dynamic responses of rocks. The cyclic disturbance or disturbance history greatly enhances the strength and brittleness of red sandstone specimens and induces more energetic fractures. The failure mechanism of red sandstone is correlated to both intercrystalline slip and microfracturing. The inclined strain bands resulting from the irreversible deformation first merge, and then several short cracks appear in the form of high-strain bands and further coalesce as the cyclic disturbances proceed. Different from the red sandstone specimen, the granite specimen starts to generate abundant microcracks at high static stress, and those cracks are further activated, blunted, and unstably propagated during cyclic disturbances, resulting in tensile failure at a stress level much lower than its UCS. In addition, cyclic disturbances can induce more major tensile cracks and promote crack branching in granite specimens. The dynamic instability of the two microstructurally different rocks is generally preceded by an abrupt increase in the AE count rate and a decrease in the b value, which can be utilized for disaster prediction in rock and mining engineering.

Highlights The coupled static-dynamic tests were performed on microstructurally different rocks.The effect of rock microstructure on the dynamic responses of rocks is clarified.The dynamic failure of rocks is preceded by an abrupt increase in AE rate and a decrease in b value.