Experimental Study on Grouting Injectivity of Artificial Rock Joints at High Temperature

The demand for the construction of geological disposal facilities has increased owing to the dearth of sustainable solutions for high-level nuclear waste management. Nuclear waste should be disposed of in deep underground spaces for long-term isolation to prevent radioactivity and overheating hazards. Several microcracks of various sizes exist in deep rock masses. These microcracks cause the inflow of groundwater and outflow of radionuclides, which can hinder the mechanical stability of the disposal facility. Therefore, cracks adjacent to storage spaces must be filled using grouting techniques. At the repository depth (500–1,000 m), the temperature exceeds 60°C owing to the thermal effect arising from radioactive waste and geothermal heat. The properties of cement grouts are affected by temperature and the water–cement ratio. In addition, the performance of cement grout is time dependent, and its viscosity varies with temperature. Considering grouting activities at high ground temperatures (e.g., 60°C), the mechanical and rheological properties (viscosity and yield strength) of grout in high-temperature environments should be investigated. In general, when grouting is performed at high temperatures, injectivity decreases owing to an increase in the viscosity and yield strength of the grouting material. In this study, laboratory experiments are conducted using micro-cement as the grout material to measure the viscosity and yield strength based on the temperature, mixing ratio, and injection time. Furthermore, artificial specimens with joint apertures of less than 1 mm are prepared for grout injection experiments. The injected distance based on different temperatures, mixing ratios, and injection times is analyzed. The injection performance of grout materials is evaluated under different temperatures (20°C–60°C). The injection characteristics are analyzed based on the relationship between the rheological properties and injectivity. Test results show that the viscosity and yield strength of the grout materials increase with temperature, thus resulting in a decrease in injectivity. The findings of this study can provide valuable input parameters for numerical simulations and basic data for in situ grouting operations at high temperatures.