Numerical Investigation on the Grouting Penetration Process of Quick-Setting Grout in Discrete Fractured Rock Mass Based on the Combined Finite–Discrete-Element Method

In this study, a combined finite–discrete-element method (FDEM)-based grouting simulator, in which the effect of time-dependent rheological characteristic caused by grout hydration on grouting penetration is adequately considered, was developed for more accurately modeling the grouting penetration process in the fractured rock mass, especially for quick-setting grout. To implement the grouting penetration process, the time-dependent Bingham model for characterizing the time-dependent rheological characteristic of grout, the flow network searching algorithm combining with the grout flow solver for solving the grout flow, and the hydromechanical (HM) coupling algorithm for characterizing the grout–rock interaction were systematically integrated into the FDEM framework. After that, to validate the developed simulator for modeling the grouting penetration of time-dependent Bingham grout and the grout–rock interaction, two benchmark tests were conducted. Finally, to further demonstrate the capability of the developed simulator, the rheological model for characterizing the cement and sodium silicate (C–S) grout, a quick-setting grout, was embedded in the simulator to simulate the grouting penetration process in the discrete fracture network. The results indicated that the developed simulator can accurately capture the effect of time-dependent rheological characteristic caused by grout hydration on the grouting penetration process. As the water–cement ratio (W/C) increased or the cement–sodium silicate (C/S) ratio decreased, both the penetration rate and grouting ratio increased significantly. Increasing the W/C ratio was more effective than decreasing the C/S ratio to increase the penetration range. Decreasing the C/S ratio can increase the grouting penetration range more significantly than increasing the grouting pressure.