The extensive development of water-conducting fractures caused by coal mining in overly-ing strata is an important cause of groundwater loss and ecological damage,and the scientific implemen-tation of water-conducting fractures permeability reduction is of great significance for the realization of ecological function restoration of mining-damaged aquifers and green mining.Utilizing the characteristics that chemical precipitation is prone to adsorption-consolidation to form plugging,the permeability reduc-tion tests of repairing single fractured rock samples with CaCO3 and Fe(OH)3 were carried out.Using Na2CO3 aqueous solution as simulated groundwater,CaCl2 aqueous solution and FeSO4 aqueous solution as repair reagent respectively,and simulating the seepage condition of fractured rock mass,the simulated groundwater and repair reagent were simultaneously injected into a single fractured rock sample at a con-stant current.Finally,the repair and permeability reduction laws of two kinds of precipitates for two dif-ferent fractured rock samples were obtained.The test results showed that the two kinds of precipitates have obvious anti-seepage effect on rock fracture,but the effect of fracture repair was different due to the difference of micro-structure and scaling mechanism between them.CaCO3 precipitation was a typical crystalline precipitation,which was nucleated by crystal adsorption and growth consolidation with com-pact structure and good stability.It was easy to have a good effect on fracture repair and permeability re-duction.The permeability reduction ranges of two rock samples were 220 times and 175 times after 400 min and 208 min,respectively.However,the precipitation of Fe(OH)3 was a typical amorphous precip-itation,which depended solely on the van der Waals force of the precipitated colloid to adsorb on the fracture surface accumulated for consolidation.The high water temperature could easily reduce the van der Waals force and caused the structure of the precipitated consolidation body to be loose,so it was dif-ficult to resist the erosion effect of high water pressure,and the permeability reducing curve was easy to"rebound"frequently in the repair process.When the test temperature was reduced from 28 ℃ to 8 ℃,the extent of fracture permeability reduction was increased from 35 times to 106 times,and the effect of repairing and reducing permeability was significantly improved.This indicated that Fe(OH)3 precipitation is suitable for repairing in shallow fractured rock mass under relatively low temperature con-ditions,while CaCO3 precipitation had a wider range of water temperature.The research results provide reference for the practice of ecological function restoration of aquifers repaired by chemical precipitation.
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