Study on freeze-thaw damage and mechanical properties of fractured rock mass grouting reinforcement in alpine region open-pit mines

To investigate the degradation of "grout-rock" interfaces caused by freeze-thaw (F-T) cycles in fractured rock bodies following grouting in cold regions, this study systematically examines the shear stress characteristics and F-T resistance of ordinary cement grout (OC), graphene oxide-modified grout (OC-I), and microsilica-modified grout (OC-II) under saturated conditions. Utilizing scanning electron microscopy (SEM), computed tomography (CT), and digital image correlation (DIC) analysis, the research characterizes the F-T damage modes, damage evolution stages, and variations in shear strength among the different grout types. The findings indicate that ordinary cement grout demonstrates inadequate F-T resistance, exhibiting a significant reduction in shear strength under F-T cycles. In contrast, the graphene oxide-modified grout enhances interface density, thereby delaying the initiation and propagation of cracks; however, the performance improvement is limited at elevated F-T cycle counts. The microsilica-modified grout exhibits the highest F-T resistance, as the calcium silicate hydrate (C-S-H) gel it produces effectively fills pores and microcracks. After 45 F-T cycles, the retention of shear strength exceeds 60 %, which is approximately double that of the ordinary grout. Furthermore, the microsilica-modified grout enhances the cementation properties at the interface and improves crack control capabilities, thereby increasing the stability of grouting materials in F-T environments. This research provides reliable and durable material option for rock reinforcement and protective engineering in cold regions.