Research On Mechanism Of Water-displacing Grouting In Mine Fractured Aquifer

Although the number of mine water accidents and deaths in China shows a downward trend in recent years,large mine water accidents still occur time to time and account for a high proportion of mine accidents,the situation is still grim,especially for the North China type coalfield with large coal reserves,the mining process of the lower coal group is generally threatened by confined aquifer in the floor of coal seam.For the above situation,grouting reconstruction of the working face floor aquifer is mainly adopted in mining to prevent water inrush from the floor of coal seam.For a long time,scholars from home and abroad have done a mount of research on the diffusion mechanism of slurry in non-water-rich fractured rock mass,and many fruitful research results have been achieved.However,there are few researches on the diffusion mechanism of slurry in water-rich fractured rock mass,so it is necessary to study systematically and analyze the slurry diffusion in water-rich fractured rock mass,and further explore the slurry diffusion mechanism in fractured aquifer to ensure the safety when mining above confined aquifer.In this paper,using the comprehensive research combined with theoretical analysis,laboratory test,numerical simulation and field cases,the mechanism of water-displacing diffusion by slurry in the single fracture was analyzed.On this basis,the mechanism of water-displacing diffusion by slurries with different flow patterns in the fracture network is analyzed,and the main research work and conclusions are as follows:（1）Dynamic equilibrium theoretical models and numerical models of Bingham slurry,power-law slurry and Newton slurry are established,which are on the basis of taking factors such as water-displacing effect of slurry,fracture roughness,time-varying of slurry viscosity under dynamic disturbance and differences of slurry viscosity at different diffusion locations into comprehensive consideration.Calculation expressions of slurry-water interface pressure,slurry diffusion distance and slurry flow of various slurry flow pattern in the process of water-displacing in the single fracture are derived,and the factors affecting the water-displacing diffusion effect of slurry are systematically analyzed.The results show that when the grouting time is the same,the slurry diffusion distance considering the effect of water-displacing diffusion by slurry is smaller than the distance without considering the effect,and the difference between the two is larger at the beginning of grouting;when the diffusion distance is the same,the smaller the yield stress,rheology Index,viscosity time-varying index and the slurry viscosity,the greater the slurry-water interface pressure and the greater the slurry inlet flow.The larger the grouting pressure and fracture width,the greater the slurry-water interface pressure and the slurry inlet flow.（2）By analogy to the circuit analysis method,a series parallel fracture network combination model was established,and the expression of seepage resistance of Bingham slurry,power-law slurry and Newtonian slurry in the flow process of single fracture was derived.Based on this,the total seepage resistance model of slurry in the water-displacing diffusion process of fracture network is established,and adopt effective media approximation method,node flow conservation and the principle of the system total pressure constant,the expressions of the flow rate and the slurry pressure corresponding to the initial grouting time and the end time of the power law slurry,Newtonian slurry and Bingham slurry under constant pressure and constant flow grouting are obtained.Based on the case analysis of water-displacing under constant pressure and constant flow in the discrete fracture network,it can be seen that under the condition of constant pressure grouting,the inflow flow q of the system decreases from the initial 2.446×10^-3m³/s to 6.230×10^-5m³/s.Under the condition of constant flow grouting,the slurry pressure P₁ increased from the initial 1.1MPa to4.93MPa.（3）Designing the visualization test system for water-displacing in fractured aquifer independently,the theoretical and numerical results are verified through the experimental analysis of the slurry diffusion distance and the slurry pressure at different diffusion locations changing with the grouting time during the slurry flow in single fracture and series parallel fracture structures,according to the water-displacing test analysis of the bifurcation fracture structure with constant pressure,the pressure value of each monitoring point after stabilization increases with the decrease of the secondary fracture gap width,and presents a linear growth law with the increase of the slurry pressure,and the closer to the grouting opening,the greater the pressure value increase.The water cement ratio of slurry has no great influence on the pressure value after each position in the bifurcation fracture structure reaches the stable value,but with the increase of water cement ratio,the total time of water-displacing diffusion decreases continuously.（4）Based on the numerical control equation of water-displacing diffusion of slurry in a single fracture,the numerical control equation of water-displacing of slurry in the fracture network with different flow pattern is established,what’s more,on the basis of the random fracture network generated by Monte Carlo method,a program was developed to extract effective fracture network.Through relevant numerical solution,the variation law of slurry pressure and inlet flow of slurry of different flow pattern in the process of water-displacing in herringbone shape fracture structure,regular fracture network and discrete fracture network are obtained.On the basis of the mutual confirmation between the numerical results and theoretical results,the sensitivity analysis of the external main control factors influencing the change degree of the slurry inlet flow in the fracture system under the condition of constant pressure grouting is carried out.The results showed that the primary and secondary order affecting the sensitivity of the change degree of Bingham slurry inlet flow are as follows:slurry viscosity,Yield stress and slurry pressure,and affecting the sensitivity of the change degree of power-law slurry inlet flow are as follows:slurry viscosity,rheological index and slurry pressure.（5）Through the analysis of transient electromagnetic detection and drilling detection of limestone in the floor of No.6 transportation roadway in Renlou Coal Mine,it is known that the limestone of Taiyuan Formation in roadway floor has certain water bearing capacity.Combined with the field pumping test data and the theoretical formula obtained in this paper,the final pore pressure value of grouting is9.89mpa.The calculated final pore pressure value is used to guide the field grouting,and based on the inspection drill On the basis of better evaluation of grouting effect,the safe driving of No.6 transportation roadway in confined fractured aquifer is successfully realizedThere are 95 figures,35 tables and 151 references in this paper...