Smolnik, G, Kouhia, A & Penczek, R 2026, 'Advances in pumpable urea–silicate resin rockbolting systems: laboratory performance of hollow-core 
bar bolts under shear and tensile loading, coupling integrity, and productivity in modern hard rock mining', in D Cumming-Potvin & J Wesseloo (eds), Ground Support 2026: Proceedings of the 11th International Conference on Ground Support in Mining, Australian Centre for Geomechanics, Perth, pp. 1-14, https://doi.org/10.36487/ACG_repo/2625_16
(https://papers.acg.uwa.edu.au/p/2625_16_Smolnik/)
Abstract: Pumpable 2-component urea–silicate resins have become an increasingly important component of modern rock reinforcement systems due to their compatibility with mechanised installation methods, rapid curing characteristics, and potential for improved installation quality and productivity. This paper presents the results of a laboratory investigation into the mechanical performance of dynamic and ductile hollow-core bar bolts grouted with urea–silicate resin, together with an evaluation of couplers used for extension drilling and a review of the operational advantages of pumpable resin technology in underground hard rock mining.
A series of tensile and shear tests were conducted at the NTNU Engineering Geology Laboratory using R28 and R32 dynamic and ductile hollow-core bar bolts installed in high-strength concrete blocks designed to simulate hard rock conditions. All specimens were tested one hour after installation. The results demonstrated high load-bearing capacity and excellent deformation characteristics of the bolt-resin assemblies. For dynamic bolts, the shear resistance exceeded the tensile resistance, primarily due to localised bolt bending and confinement effects developing within the borehole during loading.
No bond failure, resin failure, or bolt pull-out was observed in any test, confirming the rapid strength development and high anchorage performance of the urea–silicate resin system. Additional testing of couplers recovered from extension-drilling operations in hard granite demonstrated that the couplers consistently exceeded the strength of the connected bolts and did not constitute a weak link within the reinforcement system.
The paper also discusses the application of pumpable resin technology in mechanised and automated mining environments. The findings confirm that hollow-core bar bolts grouted with urea–silicate resin provide a robust and highly productive ground-support solution characterised by excellent mechanical performance, reliable anchorage, strong coupling integrity, and suitability for a wide range of underground mining conditions.

Keywords: hollow-core bar bolt, shear strength, urea–silicate resin, pumpable resin, bolt coupling