The Geomechanical Response of Axially Loaded Fully Grouted Rock Bolts Utilizing Fibre Optics Technology

Abstract

Rock bolts have been used in mining and civil engineering applications for over 40 years, and have since been one of the primary surficial support systems for underground excavation projects. The main function of a rock bolt is to stabilize the rock mass around the opening of an excavation by fastening to more stable formations behind the excavation face. The lack of discrete design criteria with respect to rock bolts, as well as the emergence of infrastructure projects in more difficult conditions has led to an increase in ground falls associated with failure of the support member. Accordingly, this research programme aimed to increase the industry’s understanding of how this support member functions by utilizing a newly developed Distributed Optical Sensing technology that provided an unprecedented spatial resolution of 0.625 mm. Fifteen (15) pull-out tests on rock bolts that were grouted within concrete specimens were conducted under similar loading conditions for different grout types, embedment lengths, and borehole sizes. The fibre optic technology was placed within diametrically opposing grooves that were machined into the bolt samples. This provided a high spatial resolution, continuous strain profile of all studied samples and therefore successfully obtained insight into the micro-mechanisms involved, overcoming the limitations of research previously conducted with conventional laboratory equipment. This rigorous testing scheme systematically determined specific support features and interaction parameters within the rock bolts. It also enabled an in-depth look at the critical embedment length and failure mechanisms associated with this type of loading. These results were then compared with ten (10) numerical models, developed within the two-dimensional finite element method numerical modelling software RS2 (Phase2 9.0). Comparisons of the results from the laboratory testing programme and numerical models showed significant differences. These differences warrant further research into utilizing the physical results to improve these numerical modelling programs used for the analysis of geotechnical structures for civil and mining applications. Overall, the results included in this thesis substantially improve upon the industry’s understanding of the inherent complexities of the axial loading mechanisms of fully grouted rock bolt support elements.