Assessing fracture mechanics in thermally treated, uniaxial loaded grouted non-persistent medium-hard rock: a digital image correlation and FracPaQ analysis

Dynamic loading along the rock joints from factors such as thermal loads, excavation, and seismic wave velocity further exacerbates susceptibility. It is crucial to restore the strength of such rock masses using appropriate techniques to enhance the stability of slopes and tunnels and mitigate future distress and damage. This study investigates the impact of uniaxial loading on the peak strength and fracture propagation behaviour of non-persistent rock masses subjected to temperatures from 100 °C to 400 °C. These parameters have been examined in jointed samples (i.e., prepared by dental plaster (DP) with joint at 30° inclinations to the horizontal in the middle of the specimen) and filled with grouts using (i) cement, (ii) sand-cement mortar (in a 1:3 ratio) and bio-concrete (SCB) mix, and (iii) epoxy resin. The results reveal that grouting can mitigate the presence of defects in any rock mass. Without heat-treated specimens with epoxy grout are more effective than those with cement and SCB mix grout. The study also clearly delineates the effects of temperature variation on the strength behaviour of both un-grouted and grouted specimens. The strain field of samples without subjected to heat treatment varies from 0.01 to 0.25, 0.05 to 0.55, 0.02 to 0.14 and 0.01 to 0.1 in un-grouted, SCB mix, cement and epoxy grouted, respectively. In un-grouted specimens, strain increases with higher thermal treatments, transitioning from tensile to far-field failure modes. When grouting is introduced, an increase in strain is observed. In specimens grouted with SCB mix, shear cracks dominate up to 250 °C, after which far-field cracks appear. In cement-grouted specimens, far-field cracks are observed up to 200 °C, followed by a transition to tensile failure mode. However, far-field failure mode in epoxy grouted specimens initiates from the onset of thermal treatments, starting at 100 °C. The detailed observations on crack propagation along un-grouted and grouted specimens is made via Digital Image Correlation (DIC) and FracPaQ analysis. The DIC technique enables precise measurement of strain distribution and deformation, while FracPaQ provides detailed analysis of fracture networks and orientations.