Investigating the effects of geothermally active temperature conditions on fully grouted rock bolts with distributed fiber optic sensors

A series of laboratory pull-out tests was conducted to study the effects of temperature on the performance and behaviours of fully grouted rock bolt specimens cured within a specific temperature range, as well as for different durations. Each specimen consisted of a 20M rebar bolt at 1300 mm embedment length grouted inside a Schedule 80 steel pipe using Portland cement grout at a 0.4 water-to-cement ratio. Two temperatures (20 °C and 45 °C) were explored to investigate the effects of geothermally active temperature conditions on fully grouted rock bolts. Distributed fiber optic sensors were employed to provide continuous strain profiles along the entire embedment length to observe micro-mechanisms and monitor internal specimen temperature change during testing. The specimens cured at 45 °C generally resulted in higher grout UCS (in certain cases 25%-50% higher) compared to those at 20 °C; the ultimate capacity was not significantly impacted as the specimens’ embedment length allowed full development of the rock bolt’s capacity. The resulting strain profile trends showed generally higher strains experienced by the shorter (i.e. 3-d) curing duration specimens under both curing temperatures compared to long-term curing. The 45 °C specimens generally experienced lower strains and faster strain profile attenuation compared to specimens cured at 20 °C. Understanding these effects and further analysis of FGRB specimen behaviours over time provide insights for mobilized and critical embedment lengths, capacity development, and support system stabilization. This paper highlights the results of this study and aims to bridge selected gaps in existing literature with a view to aid practitioners.