Stability Analysis And Treatment Of Large Gently Inclined Empty Area Formed By The Caving Method

The caving method has the advantages of large production capacity and high efficiency,so it is widely used in non precious metal mines.In caving method,the ground pressure is controlled by the roof caving to reach enough thickness of overburden.In a certain iron mine,no pillar sublevel caving method is used to mine the ore body,roof caving is not up to expectation,forming a large and gently inclined empty area,which has affected the safety and production of the mine.Therefore,it is urgent to analyze the stability of the large-scale goaf,which is of guiding significance for mining enterprises to determine the risk degree of the goaf,to control the goaf in time and to recover the ore body in the lower part of the goaf safely and effectively.In this paper,based on the research background of the large empty area,the stability of the large empty area is analyzed by means of field investigation,theoretical analysis,numerical simulation,field monitoring and other means,and the necessary control measures are put forward.The main research contents and achievements of this paper are as follows:(1)On the basis of consulting the geological and production data of the mine and full field investigation of the mine,we can know the general situation of the mine,find out the current situation,causes and characteristics of the goaf,summarize the factors affecting its stability,and provide data support for the fuzzy evaluation of the goaf.(2)The weight values of 14 factors affecting the stability of goaf are determined by AHP.According to the results of AHP and fuzzy mathematics theory,a two-level fuzzy comprehensive evaluation model of goaf is established to evaluate the stability of large goaf.The risk degree of goaf is grade IV and the stability of large goaf is poor.(3)3D mine is used to build the ore body model,and FLAC3 D is used to simulate the excavation of the ore body numerical model.From the numerical simulation results,it can be seen that the decline value of each line displacement of the roof in the empty area is 1.78 ~2.92 cm,the roof tensile stress concentration is obvious and the maximum value is 0.67 mpa,the plastic area is wide and shows shear and extension failure,and the stability of the roof 3-5line is the worst,which further shows that the stability of the big empty area is poor.(4)The roof caving of No.4 borehole(line 5)is 29.65 m,which is monitored by the borehole video instrument,and the reliability of the research results of fuzzy evaluation theory and numerical simulation is verified.According to the fact of roof caving,a roof spanair coupling model is established to study the law of roof caving and the change of impact wave with caving height(time)speed.When t = 1.425 s,the maximum velocity of the roof falling block is 12.41m/s,and the maximum velocity of the impact wave at the roadway crossing is 724.92m/s.(5)Taking full account of the actual situation of large goaf,combined with the existing methods of goaf treatment,this paper puts forward a method of goaf treatment with filling as the main part and closed wall as the auxiliary part.Through the experimental study,the best filling proportion is obtained,and the numerical simulation is used to verify that the filling treatment method is feasible and effective.