Abstract: The second-generation negative Poisson’s ratio (2G-NPR) bolts are increasingly being applied in the reinforcement of fractured rock masses. Direct shear tests were conducted to compare and analyze the shear mechanical behaviors of 2G-NPR anchor bolts and conventional steel (Q235) bolts in anchored joints with different filling thicknesses. The results showed that, under the same filling thickness, the 2G-NPR bolts exhibited lower shear stiffness in the elastic stage, higher peak shear strength, and greater peak shear displacement compared to the Q235 bolts. As the filling thickness increased, although the changes in peak shear strength between the two types of anchor bolts were not significantly different, the 2G-NPR bolts displayed a notable advantage in peak shear displacement due to their high energy absorption and high ductility characteristics, resulting in improved specimen ductility. Axial force monitoring data revealed that the 2G-NPR bolts effectively compensated for the sudden axial force drop caused by decoupling with the grout and demonstrated more sustained load-bearing capacity. Their average peak axial force was 3.14 times that of Q235 bolts, and the peak axial force continued to increase with the filling thickness, indicating more stable anchoring performance. Acoustic emission (AE) monitoring further revealed that, under the same filling thickness, the 2G-NPR bolts had lower maximum cumulative counts and maximum cumulative energy, with a later decrease in the b-value (the ratio of small to large AE events), leading to less damage to the specimens. This indicates that the enhanced ductility of the specimens reinforced by 2G-NPR bolts is due to their effective absorption of shear strain energy, which slows the propagation of cracks. These findings provide guidance for the application of 2G-NPR bolts in supporting rock masses with weak interlayers.

Key words: 2G-NPR bolts, infilled joints, shear performance, axial force, acoustic emission characteristics