Abstract: In order to study the influence of the cross joints on the fracture mechanism of rock mass, a joint model that can simulate the cross structural plane of rock mass was prepared by the 3D printing technology. By pouring similar materials, the specimen with prefabricated cross joints was formed. Based on the digital image correlation technology (DIC), the crack initiation, propagation and failure mode of specimen under uniaxial compression were analyzed. The results show that the closed joint model made by 3D printing technology can effectively replace the open joint fissures formed by traditional cutting or slotting methods. The experimental results show that the cross joints can significantly reduce the rock strength. With the increase of the cross joint angle, the strength of specimen increases firstly and then decreases. It reaches the maximum value when the cross joint angle is between 45o and 60o. The peak strain presents an opposite variation rule with that of the rock strength. The process of crack growth can be divided into four stages: the microcrack closure stage, the microcrack development stage, the initiation of main joints and the rapid extension of secondary joints, which correspond to each stage of stress-strain curve. It is also found that the influence of secondary joints on the failure of rock with cross joints is mainly reflected in the post peak stage. Combined with the maximum distortion energy theory, it has little influence on the stress distribution at the tip of the main joints, which play an absolute role in controlling the rock failure. This has a certain guidance for rock engineering.

Key words: 3D printing, cross joint, uniaxial compression, digital image correlation (DIC), crack propagation