Study On The Stability Of Ground Near Surface Mining In Ningdu Pyrite Mine

With continuous development of modern economy, the demand for mineral resources is keep increasing, while the long-term underground mining of mineral resources caused many security problems, which led huge loss to enterprises and nation. On the road of sticking to sustainable development strategy and harmony between man and nature, the earth pressure instability due to underground mining must be taken seriously and settled.In this paper, a study of the goaf stability of ground pressure caused by years of pyrite exploitation has been carried on combining with subject "Ningdu pyrite pressure stability monitoring and research". Using of on-site investigations, theoretical analysis, numerical simulation and local monitoring, to analyze ground pressure variations and ground surface subsidence due to pillar mining near the earth’s surface, the main research contents and achievements are as follows:(1) Collecting relevant data and field surveys, sorting and analyzing mine geology, mining situation, goaf form, underground mining progress, mining instability, etc, to provide a basis for following work.(2) Mechanism analyzing pillar mining near the earth’s surface, summarizing the reasons and factors affecting surface subsidence, qualitative analyzing and evaluating the general law of pillar mining and subsidence near the earth’s surface. Using the grey prediction system for predicting the surface subsidence value, to determine the stability of mine excavation.The results show:the width of the core area of the pillar is two times greater than the width of yield zone, a>2b, the pillar K value is greater than 1, show that the stability of pillars; The overburden can remain stable, not a sudden failure.(3) SURFER is to establish terrain model, SURPAC is for subsurface model, uniting these two models to set up mine three-dimensional model, ANSYS is for mesh division, FLAC3D defines material nature and static boundary condition, apply initial stress to analyze static force, mining in steps and sections to get surface vertical and horizontal displacement after excavation,to determine the stability of mine excavation.The results showed that after the excavation of the maximum displacement variation value of X direction 3.2cm respectively, 1.16 cm in Y direction, Z direction 8.2cm, the mining area surface will not occur sudden instability collapse.(4) Lay monitoring network on areas for long-term monitoring, analysis and sort monitoring data. Long-term monitoring shows that the observation period the maximum displacement point for BM5 observation points, displacement value for 51.88mm. The results show that the mine did not occur large-scale destruction, but in the future to continue mining must cause enough attention.