SAFETY ISOLATION LAYER THICKNESS AND ACOUSTIC EMISSION MONITORING OF CAVITY UNDER OPEN PIT BENCHES

There have many open pits in China threatened by cavities under open pit benches because of former unreasonable underground mining.Shape and size of these cavities were greatly changed through many years mining activity.There have no clear figures or data to show how these cavities occurred.This would greatly restrict high-efficient and safe mining.Thus,the reasonable safety isolation layer thickness of cavity should be properly calculated,and the feasible stability monitoring method for this kind of cavity should be employed to well ensure safety of personnel and equipments on open pit benches.Based on the present situation of Sandaozhuang open pit of Luoyang Luanchuan Molybdenum Group Inc.,which has lots of cavities under its benches,the safety isolation layer thickness corresponding to different roof spans,which can provide a primary evaluation for cavity stability,was obtained through numerical modeling.Acoustic emission technique was used to monitor the cavity stability.Monitoring data of four types of cavity,i.e.unstable cavity,stable cavity,cavity with drill and cavity after blasting,which are all the typical ones under open pit benches,were listed.The signals of acoustic emission of those cavities were analyzed to obtain acoustic emission characteristics of typical cavities under open pit benches.This will provide reference for following accurate stability evaluation of cavities under open pit benches that are monitored by acoustic emission technique.Thereupon,the efficient safety guarantee system of open pit benches with cavity would be established through primary evaluation according to safety isolation layer and stability monitoring by the acoustic emission technique.