Experimental study on water permeability decrease character due to restoration function on chemical precipitation on holes or fractures in mining failure rock mass

Aiming at the problem of ecological restoration of overburden aquifer caused by mining activities，oriented to an idea that blocking mining-induced fractures with chemical precipitation，some experiments on the permeability reduction characteristic of mininginduced fractures were conducted.To simulate the flowing state and percolation of underwater in the mining-induced fractures，the singlefracture rock model and the quartz sand tube model was built.The permeability reduction characteristic can be evaluated while injecting chemical ferric and calcic reagent，the process of which can generate precipitations.The results showed that there was a considerable reducing trend of permeability during the 42 days experiment，furthermore，the permeation speed changed，being fast firstly and then slow.In the single-fracture rock model，the absolute permeability decreased from 15.1 μm2 previously to 0.01 μm2 after experiment，as blocked with ferric chemical precipitation.Because of the water-swelling effect of clay minerals on the fracture surface，the permeability reduction showed a rapid drop in the initial stage of the experiment.As for the other model，calcic chemical precipitation was used accordingly，with the permeability reducing from 62.3 μm2 initially to 0.1 μm2.Due to the large size of macroscopic holes and high initial porosity (32.8%)，the duration of initial process of permeability reduction was significantly longer，furthermore，the absolute permeability values was also larger at the end of the experiment.The experimental result indicated a positive effect of ferric and calcic chemical precipitation on blocking mining-induced fracture，also provided a reference for researches and practices of aquifer restoration after mining based on blocking underground channels in the bed rock through a chemical approach.