Analysis Of Ground Gravity Anomaly Effect In Mine Goaf

Plenty of underground mine goaf formed by coal mining are safety hazards to coal mine production and mining area construction.Its effective detection and stability evaluation are important subjects in academic community.The "cavity" effects of underground goaf will lead to the change of gravitational field.The evolution characteristics of goaf can be revealed by surface gravimetry.But for a long time,this kind of gravity anomaly effect has been neglected for its small magnitude.Starting with the experiment of high-accuracy gravimetry,this paper analysis the ground gravity anomaly effect of goaf by numerical simulation and experimental validation,and explore the technical approach of invert goaf stability based on gravity anomaly data.The main contents and results are as follows:(1)Based on the idea of finite element method and probability integration model,the forward model of ground gravity anomaly in coal mine goaf is constructed and the regularities of distribution of ground gravity anomaly caused by goaf is analyzed.The results show that the gravity anomaly field of goaf is distributed symmetrically above the cavity.The gravity anomaly effect caused by goaf under general mining conditions is about 50uGal?450uGal.The peak gravity anomaly of ground is positively correlated with the width and height of mining.There is a nonlinear negative correlation between the peak of ground gravity anomaly and the buried depth of the cavity.(2)Performed gravimetry by using CG-5 Auto-gravimeter and analyzed the reliability of high-accuracy gravimetric data.Experimental results show that the static observation accuracy of Auto-gravimeter is ± 5uGal,and its dynamic observation accuracy is ±3.5uGal.At the same time,after filtering and unified naturalization,the naturalization residuals of gravimetric observation data are within±10uGal,far less than the minimum peak of ground gravity caused by goaf.It is proved that the weak ground gravity anomaly of goaf can be observed by CG-5 Auto-gravimeter,gravimetry.(3)The inversion model of ground gravity anomaly in coal mine goaf is constructed by using the compact difference scheme and the influence of measurement error on the accuracy of cavity boundary inversion is analyzed.The numerical simulation shows that when the random error does not exceed ±15uGal,the position of cavity boundary can be inverted accurately.(4)Through the gravity detection experiment of underground cavity,the validity of the inversion model is verified.Experimental results show that the precision of high-accuracy gravimeter(CG-5 gravimeter)and its data reliability can meet the requirements of inversion model on gravimetric accuracy,which provides a new technical method to invert the goaf evolution and its ground perennial stability by using gravity anomaly data.