Stability analysis of section coal pillar at a fully-mechanized working face based on axial bolt load tests

In the mining area of western China,double entries are mostly excavated simultaneously at one end of a fully mechanized working face in order to keep the normal continuance of mining and excavation and realize a high produc- tion and efficiency of coal mine. Mine pressure appears very serious at the section coal pillars between two entries after they are disturbed by the excavation,two times of mining. Nondestructive tests of axial loads of bolts in coal pillars were performed at the severe mining influence areas of section lanes before and after the working face using a nonde- structive testing technique. The real time bolt supporting state of section coal pillars and its stability evaluation were analyzed based on the test results. At the same time,reasonable suggestions were put forward for the forepole reinforce- ment measures of coal pillars. The research results show that the axial bolt load increases to peak and then decreases, until stable in an overall change trend in the entries when the distance if testing bolts is far from the working face. The peak axial bolt load is located exactly at the border area of severe destruction and undamaged area of section coal pil- lars. Severe mining influence scope before and after the working face can be better reflected by the changes of axial bolt loads,which provide a good reference for the forepole support scope of section entries and its prevention and rein- forcement measures.