Key Takeaways & Executive Findings
- •• 2G-NPR bolts significantly enhance the shear strength and deformation capacity of saw-tooth rock joints compared to unbolted conditions. • 2G-NPR bolts outperform Q235 steel anchors by providing superior toughening and crack-arresting effects under shear loading. • The improvement in shear strength and displacement offered by bolting decreases as the saw-tooth angle of the joint increases. • The combined laboratory and numerical approach provides a reliable basis for applying 2G-NPR bolts in jointed rock mass stabilization.
Abstract
The shear performance of bolts plays a crucial role in controlling rock mass stability, and the roughness of the joint surface is one of the main factors affecting the mechanical properties of anchored joints. The 2nd generation of negative Poisson ratio (2G-NPR) bolt is a new independently developed material characterized by high strength and toughness. However, the influence of joint surface roughness on its anchorage shear performance remains unexplored. This study involves preparing regular saw-tooth jointed rock masses and conducting laboratory shear comparison tests on unbolted samples, 2G-NPR bolts, and Q235 steel anchors. A three-dimensional finite element method, developed by the author, was employed for numerical simulations to analyze the influence of saw-tooth angles on the shear resistance of anchored bolts. The findings show that the anchorage of bolts enhances the shear strength and deformation of saw-tooth rock joints. The 2G-NPR bolts demonstrate superior performance in shear strength and deformation enhancement compared to Q235 steel anchors, including improved toughening and crack-arresting effects. Furthermore, the improvement of the shear strength and displacement of the bolt decreases with the increase of the joint saw-tooth angle. These findings provide a valuable test basis for the engineering application of 2G-NPR bolts in rock mass stabilization.
1. Introduction
Bolt support is a widely used method for stability control in geotechnical engineering [1−6]. A combination of excavation disturbance, geological tectonic movement, and complex stress field can lead to the formation of rock joints, cracks, and faults. These defects considerably damage the integrity and continuity of rock mass, making it prone to dislocation, separation, and other forms of shear deformation along the structural planes. Such deformations can result in shear or tensile fracture of the bolt, posing significant safety and control challenges [7−11]. Therefore, understanding the mechanical properties of bolted rock joints under shear load has become a key research focus in geotechnical engineering.
BJURSTROM [12] was the first to conduct the shear experiment of rock mass with anchored joints. Subsequently, numerous scholars studied the anchorage shear characteristics of bolts. Based on the laboratory shear test and numerical simulations, a variety of studies explored key test variables such as anchoring angle [13−16], joint roughness [10, 17, 18], rock strength [14, 19, 20], and bolt type [21−24], and load mode [25, 26]. These studies have elucidated the normal constraint and tangential shear action mechanism of bolt on jointed rock mass.
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Ren Shu-lin, He Man-chao, Yuan Yong, Tao Zhi-gang, Zhu Chun, Yin Qian (2025). Influence of the saw-tooth angle of rock joints on the shear performance of 2G-NPR bolt. Journal of Central South University. https://doi.org/10.1007/s11771-025-6002-7
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Frequently Asked Questions
What is a 2G-NPR bolt?
The 2nd generation negative Poisson ratio (2G-NPR) bolt is a newly developed material with high strength and toughness, designed for rock support applications. It exhibits superior shear performance compared to conventional steel anchors.
How does the saw-tooth angle of rock joints affect bolt shear performance?
The study found that as the saw-tooth angle increases, the improvement in shear strength and displacement from bolt reinforcement decreases. In other words, 2G-NPR bolts provide greater relative enhancement for lower saw-tooth angles.
What research methods were used in this study?
The researchers conducted laboratory shear comparison tests on unbolted samples, 2G-NPR bolts, and Q235 steel anchors using regular saw-tooth jointed rock masses. They also performed three-dimensional finite element numerical simulations to analyze the influence of saw-tooth angles.
Why are 2G-NPR bolts better than traditional steel anchors?
Compared to Q235 steel anchors, 2G-NPR bolts demonstrated superior performance in enhancing shear strength and deformation, and they provide improved toughening and crack-arresting effects, making them more effective for stabilizing jointed rock masses.
What is the practical significance of this research?
The findings provide a valuable test basis for the engineering application of 2G-NPR bolts in rock mass stabilization, helping to improve the design of bolting systems for joints with different roughness levels.
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