Experimental study on grouting injectivity in high-temperature environments for deep underground structures

• High-temperature (60 °C) effects were analyzed for cement grout injectivity. • Injection test was conducted using artificial single joint with 0.5 mm aperture. • Micro-cement grout shows better viscosity stability to temperature and time than OPC. • High temperatures increase viscosity growth, reduce flow rate, and minimize bleeding. • An optimized grout mix design with a W/C of 2.0-3.0 using micro-cement was proposed. Deep underground structures have been extensively developed due to urban expansion and constraints on surface land use. In deep rock masses (500–1000 m), the presence of numerous joints, fractures, and high-temperature environments poses significant challenges (e.g., groundwater inflow). Accordingly, rock grouting is necessary to enhance hydraulic impermeabilities and mechanical stabilities of rock formations. For successful grouting, using grouting materials and mixing designs optimized for application under high-temperature conditions is important to ensure effective injection. In this study, the injectivity characteristics of grouting materials under high-temperature conditions were verified through viscosity and injection tests. Micro-cement and Portland cement were used as grouting materials, with water-cement ratios (W/C) of 1.0, 2.0, and 4.0, and temperatures ranging from 20 to 60°C were employed. Viscosity measurements were conducted to analyze the effects of cement type, W/C, time, and temperature on the rheological properties of grouting materials. An experimental setup simulating a 0.5-mm single joint was utilized to evaluate injectivity by examining the injection distance and flow rate. According to the experimental findings, micro-cement with a W/C range of 2.0–3.0 was proposed as an optimal grout design for rock grouting in high-temperature environments.