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

The grouting process is an important subject 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. Taking the multi-source information as the indication, this paper presented an experimental study about the process of grouting colloidal nano-silica into 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 presented an obvious three-stage regularity. The time-dependent curves of outlet density and outlet resistance were consistent with that of pump pressure, while the curve of inlet density was opposite to pump pressure. The law of the dominated penetration mechanism was as follows: miscible displacement mechanism in the 1st stage (0-46th minute), Darcy flow in the 2nd stage (46th∼200th minute) and filtration flow in the 3rd stage. This research can guide grouting theory study and design in the over-broken rock mass.