Acoustic emission characteristics of creep fracture evolution in double-fracture fine sandstone under uniaxial compression

Acoustic emission (AE) experiments were carried out to study short-time creep behavior under uniaxial compression for cuboid-shaped fine sandstone specimens with two pre-existing cracks (the sample scale was 70 mm x 70 mm x 140 mm and the lengths of cracks were 2a = 20 mm and 2a = 30 mm) using the RLJW-2000 servo-controlled triaxial rheological test system of rock and PCI-II AE system. Based on the experimental results of creep curves, the mechanical properties of specimens with different pre-existing crack lengths were analyzed. The experimental results showed that compared to the intact specimen as the standard, the specimens with preexisting crack lengths of 20 and 30 mm exhibited a decrease in the creep damage strength from 160.4 to 100 and 55 MPa, respectively. The pre-existing crack length significantly affected the strength of the specimen. Based on the experimental results of the spatial evolution of AE events, the three-dimensional evolution law of micro-cracks in the specimens was studied. The experimental results showed that the AE events could well reflect the crack evolution process of specimens with cracks. The occurrence of AE event points was mainly due to the initiation and propagation of micro-cracks within the sample; and with the increase of stress levels, the distribution of event points exhibited different characteristics. In the first two stages of creep loading, AE events were produced to a lesser extent and were evenly distributed inside the sample. With the increase of the creep stress level, the AE activity increased, in particular at the four ends of pre-existing cracks, and evolved from the ends of the fissures, thereby enabling the prediction of the penetration position of the micro-cracks within the fractured rock mass. Moreover, AE location results also directly reflected the interior stress field propagation process. AE location results directly reflected the spatial position, direction, and spatial curved face of crack propagation in the rock sample with pre-existing cracks, which are extremely significant to study the mechanism of rock failure.