Hanging roofs or high hang-ups.a common problem in sublevel caving mining,usually result in a large ore loss and undermine mining safety.This paper analyzed the formation of a hanging roof and showed that increased co...Hanging roofs or high hang-ups.a common problem in sublevel caving mining,usually result in a large ore loss and undermine mining safety.This paper analyzed the formation of a hanging roof and showed that increased confining pressure and reduced free surface were its main characteristics.In order to break down a hanging roof,a new method based on shock wave collision and stress superposition was developed.In this method,two blastholes containing multi-primer at different positions are simultaneously initiated at first.By doing this,a new free surface and a swell room can be created.After these holes are fired,a long delay time is given to the next blasthole so that the fragments from the first twohole blasting have enough time to fall down.This new method was applied to three hanging roofs in one production area,and all of them were successfully broken down.Field inspection indicated that almost no damage was caused in the nearby drifts/tunnels due to the new method.In addition,the far field vibrations were found to be smaller than the maximum vibrations induced by some other blasts.展开更多
We present a non-contact optical investigation of laser-induced plasma at moderate Ar pressure ranging from 1 to 100 Pa.The significant shock front and spatial fractionation among the different charged ions are demons...We present a non-contact optical investigation of laser-induced plasma at moderate Ar pressure ranging from 1 to 100 Pa.The significant shock front and spatial fractionation among the different charged ions are demonstrated at the pressure of 20 Pa.The collisions between Si IV ions and ambient Ar atoms generate distinct and excited ArⅡions,fresh SiⅢions,and electrons at the dense layer.The electron density peaks at the position of the shock front,indicating that the collision that yields electrons is dominant over the recombination process in the region of the shock layer and its immediate vicinity.展开更多
文摘Hanging roofs or high hang-ups.a common problem in sublevel caving mining,usually result in a large ore loss and undermine mining safety.This paper analyzed the formation of a hanging roof and showed that increased confining pressure and reduced free surface were its main characteristics.In order to break down a hanging roof,a new method based on shock wave collision and stress superposition was developed.In this method,two blastholes containing multi-primer at different positions are simultaneously initiated at first.By doing this,a new free surface and a swell room can be created.After these holes are fired,a long delay time is given to the next blasthole so that the fragments from the first twohole blasting have enough time to fall down.This new method was applied to three hanging roofs in one production area,and all of them were successfully broken down.Field inspection indicated that almost no damage was caused in the nearby drifts/tunnels due to the new method.In addition,the far field vibrations were found to be smaller than the maximum vibrations induced by some other blasts.
基金supported in part by the National Natural Science Foundation of China(No.61805279)。
文摘We present a non-contact optical investigation of laser-induced plasma at moderate Ar pressure ranging from 1 to 100 Pa.The significant shock front and spatial fractionation among the different charged ions are demonstrated at the pressure of 20 Pa.The collisions between Si IV ions and ambient Ar atoms generate distinct and excited ArⅡions,fresh SiⅢions,and electrons at the dense layer.The electron density peaks at the position of the shock front,indicating that the collision that yields electrons is dominant over the recombination process in the region of the shock layer and its immediate vicinity.
