Grouting is commonly used to decrease the hydraulic conductivity of the fractured rock masses and control the groundwater inflow. Since underground facilities were constructed in various geological conditions, different types of grout material and mixing/injection methods were developed for effective and economical grout injection. It is also important to evaluate the grout arrival distance and the range of altered hydraulic conductivity field after grout injection. However, the mechanism of grout injection process has not been clarified sufficiently yet due to complicated chemical and physical processes of grout. In this study, to simulate the grout injection process, the three-dimensional numerical model based on equivalent continuum approach was developed and applied to the in-situ grout injection tests at the Grimsel test site, Switzerland. In the simulations, the injection pressure and/or injection rate was given as a boundary condition and total amount of injected grout (silica sol) was calculated. The breakthrough curves (grout arrival time and time evolution of grout density) at the observation boreholes and the distribution of altered hydraulic conductivity field were also investigated. The simulation results were also compared with the ones obtained from in-situ measurements/monitoring and show qualitatively good agreement.

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