Abstract: The cross joints, which are ubiquitous in real rock mass, have significant influences on the fracture characteristics of rock mass but it has not been thoroughly studied. In this paper, the 3D printed samples with cross joints are made. The mechanical fracture characteristics of rock samples with cross joints under uniaxial compression are studied by means of acoustic emission, CT scanning technology and DIC image analysis. The results show that the relationships between fracture fractal dimension (DB) and uniaxial strength, elastic modulus and Poisson’s ratio have similar trends when the dip angle of primary joint is small, which has a better accordance than that of a much larger primary joint dip angle. There is a much better regularity of fracture mode of the former than that of the latter. When the dip angle of the primary joint is large, the clustered microfracture AE events occur under the tension between the joint and the block in the compaction and elastic stages, while this phenomenon will not occur when the dip angle of the primary joint is small. In DIC strain nephogram, the micro strain on the fracture propagation path is prior to the macro fracture. The fracture mode can be predicted by calculating the maximum area of micro strain under compression. The primary joint plays the main role in the fracture initiation angle and fracture propagation mode, and the acoustic emission and fractal characteristics are unified. When the secondary joint is parallel to the maximum principal stress, the total rock damage is mainly caused by the propagation of the primary joint, and the accumulative AE events (AAEE) and DB are the largest, implying that the fracture mode is more complex when the AAEE and DB is much larger. The three-dimensional fracture mode is mainly characterized as 2-3 tension wing fracture surfaces caused by the expansion of joints ends. On the internal three-dimensional macro fracture surface, there are discontinuous structures affected by incomplete tension failure.

Key words: 3D printing cross joints, acoustic emission, CT scanning, DIC, fracture characteristics