Investigation of crack propagation behavior of opening single fractured rock based on acoustic emission technology

The fissure morphology has an important influence on rock mechanical properties and crack propagation behavior. A series of uniaxial compression tests were carried out on the intact granite samples and granite samples with different prefabricated fissure dip angles (0°, 15°, 30°, 45°, 60°, 75°, and 90°). Simultaneously, the rock failure process was monitored and recorded by acoustic emission (AE) and high-definition camera, respectively. As the fissure dip angle increases, the test results indicate that the crack initiation angle of rock decreases gradually; the peck strength, crack initiation stress, and peak strain of all the fractured rocks are increased gradually. The elastic modulus of rock increases firstly and then decreases with the increase of fracture dip angle. The initial compaction section and linear elastic section of the rock stress-strain relationship curve correspond to the quiet period of acoustic emission. The acoustic emission enters the development period after the load exceeds the crack initiation stress. When the load approaches the peak strength, the acoustic emission is in the peak period until the rock failure completely. The lager the fracture dip angle, the longer the peak duration period of acoustic emission and the more in quantity of the cumulative ringing count. A good linear relationship is presented between fracture rock peak strength and cumulative ringing count, and the influence of crack shape on rock strength damage is quantified. With the increase of fissure dip angle, the fracture mode of rock gradually transitions from shear fracture to tensile fracture. According to the relationship curves between rock axial stress and cumulative AE impact number, combined with the calculation method of rock initiation stress, It found that the calculated value is slightly larger than the camera observation value with the error range of 1.7% ~ 6.9%, indicating that the calculation method of rock crack initiation stress is reasonable. This study provides basic information for investigating the engineering properties and failure mode of fracture rock.