Experimental study of the mechanism of grouting colloidal nano-silica in over-broken coal mass

Grouting is an important process for stability control of unfavourable geology. A multi-parameter grouting monitoring device was designed to monitor pump pressure, inlet density, outlet density, outlet electrical resistance and osmotic pressure. On the basis of multi-source information, this paper presents an experimental study of the process of grouting colloidal nano-silica into an over-broken coal mass, which was verified by percolation mechanics theory and numerical simulation simultaneously. The porosity and permeability of the injected sample were 15.34% and 5.45 mD. The results showed that the variation of pump pressure generally showed an obvious three-stage regularity. The time-dependent curves of outlet density and outlet resistance were consistent with that of pump pressure, whereas the curve of inlet density was opposite to that of pump pressure. The law of the dominant penetration mechanism was as follows: miscible displacement mechanism in the first stage (0-46 min), Darcy flow in the second stage (46-200 min) and filtration flow in the third stage. This research can guide grouting theory study and design in an over-broken rock mass.