Dynamic behaviors and bolt-strengthening effect of sand-powder 3D printing rock analog under static and dynamic coupled loading

In deep mining, surrounding rock mass are subjected to high in-situ stress and dynamic loading, which leads to the difficulties in maintaining the roadway stability. Therefore, it is important to investigate the mechanical characteristics of rock bolts and their ability to enhance stability when exposed to static and dynamic coupled loading (SDCL). 3D printing technology can effectively address the challenges of preparing weak rock specimens and overcoming high variability. Consequently, the Split Hopkinson pressure bar (SHPB) is used to conduct SDCL testing on 3D printing specimens with varying bolted lengths. The similarity in mechanical performance between sand-powder 3D printed specimens and natural coal specimens has been validated. The rock dynamic characteristics with different bolted lengths under SDCL of specimens were explored. The macroscopic fragmentation and microscopic electron microscope scanning were used to reveal the dynamic failure characteristics of specimens. The study shows that static, dynamic and combined strength are positively correlated with bolted length. The dynamic strength is negatively correlated with the axial stress, and the combined strength initially increases and then subsequently decreases as the axial stress increases. The dynamic strength and the combined strength are positively correlated with the impact pressure. Efficient prevention of specimen fracture was achieved by increasing the length of the bolted connection. It can be found that at the meso-scale, when the specimen is only under the static loads, the cross-section particles are fractured along particle bonding, and under the SDCL, there are fractured along particle bonding and fractured through particle. The conclusions obtained can offer a foundation for conducting dynamic rock mechanics experiments using sand-powder 3D printed specimens and for controlling the surrounding rock in dynamic pressure roadways.