Axial load transfer mechanism of rock bolts

Axial load transfer mechanism of rock bolts

Rock bolts are widely used in mining and geotechnical engineering. They can effectively improve the stability of rock mass, reducing the rock mass deformation, and resulting in improvements in safety, cost and time. Nonetheless, a comprehensive assessment of fully grouted rock bolts is necessary, particularly under diverse geotechnical scenarios. Gaps in knowledge persist concerning their behaviour at elevated temperatures, within triaxial confinement, and under varying encapsulation length, grout properties, and rock mass attributes. Furthermore, the impact of commonly employed protective plastic sheaths, used for protecting steel rock bolts against corrosion, on the axial behaviour of these bolts remains ambiguous in the existing literature. These aspects of reinforcement systems have been understudied, restricting practical implementation. This thesis undertakes both experimental and analytical investigations into the axial behaviour of fully grouted rock bolts. The first paper examines the mechanical, thermal, and bonding characteristics of commonly used anchoring Unsaturated Polyester Resins (UPR) under elevated temperatures, revealing significant impacts above 150°C. The second paper delves into pullout performance under triaxial testing, uncovering how non-uniform confining stress on cubic samples influences bearing capacity, bonding stiffness, and lateral deformation. The third paper delves into the factors affecting axial load transfer mechanisms in fully encapsulated rock bolts, investigating embedment length, bonding material characteristics, and host rock conditions. The study unveils that increasing embedment length enhances pullout capacity up to a critical length, beyond which ultimate strength and bond stress distribution stabilise. Notably, the shear modulus of bonding materials was found as the most influential factor in axial load transfer and bond stress distribution. Lastly, this study explores the axial behaviour of fully grouted protective sheathed rock bolts. The findings indicate the vulnerability of the grout-sheath interface amongst the other features, mainly if the encapsulation length falls short. The outcomes of this research significantly enhance our comprehension of the axial load transfer mechanism of fully grouted rock bolts across various conditions. Moreover, these findings hold practical value in guiding the design, modelling, manufacturing, and application of reinforcement systems within domains like mining, tunnelling, underground excavations, and slope stability.

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