Influence of different 3D occurrences of parallel double flaws on the failure characteristics of hard brittle rock

Previous 2D fractured rock studies and tests mainly focused on the discontinuity of fracture structures along the flaw inclination direction, while there were few researches on the discontinuity or concealment characteristics of flaws along the flaw strike direction.

To this end, the hard-brittle rock-like specimens contained two parallel flaws with three types of flaws concealment conditions (two 2D flaws/ two 3D internal flaws/ one 2D flaw and one 3D internal flaws) were prepared. After the uniaxial compression test accompanied with Digital Image Correlation (monitored the secondary failures on surface) and Acoustic Emission (monitored the secondary failures inside the specimen) tests, the failure characteristics of corresponding specimens were obtained.

The concealment conditions of the parallel flaws mainly influenced mechanical properties of the above specimens. The flaw concealment conditions (proportion of the 3D flaw) had significant effects on the distributions of the external and internal secondary failure structures. In addition, the higher the proportion of the 3D flaw, the greater the difference between the internal and surface failure structures of the specimen.

Especially, when both 2D and 3D preset flaw existed in the specimen, the local failures occurred around the internal flaw kept hidden and never showed on the outside surface of the specimen; when the specimen only contained the 3D internal flaws, this kind of 3D sample had higher strength, faster failure process, more severe damage behaviors and more concealed process of destructions than that of the corresponding 2D sample.

In summary, the initiation and development characteristics of the secondary failures occurred near the 3D internal flaw can provide important reference to underground engineering under similar 3D conditions, which help to predict, prevent and control the corresponding destructions of rock.