Breakage characteristics and mechanized mining experiment in deep hard rock

In order to investigate the influence of mining-induced stress conditions on rock cuttability and mining efficiency, biaxial, uniaxial and free confining stress conditions were established. A true triaxial test apparatus was used to conduct the rock fragmentations on cubic granite specimens, corresponding to the work face in single-face driving, peninsula-type or island-type pillar and ore-rock in excavation damage zone, respectively. Four mining methods, i.e., cantilever roadheader, milling head mounted on excavator, high-frequency impact head mounted on excavator, and high-frequency impact head mounted on carry-scraper were tested to cut orebody in excavation damage zone. The results indicate that the requirements of cutting force and cutting work of lard rock are lower, and the cuttability is higher in lower uniaxial confining stress than in other stress conditions. The induced entries, which are excavated for changing the biaxial confining stress condition into the uniaxial and for inducing fractures to decrease confining stress in rock pillar, can be used to increase the applicability of non-explosive mechanized mining method for deep hard rock. The field measurements reveal that the excavation damage zone in peninsula-type pillar presents a U-shaped distribution, the thickness of which ranges from 1.84 m to 2.54 m. The cantilever roadheader, which is based on the multi-pick rotating cutting, has the highest mining efficiency and stability, and the continuous mining process has the average work efficiency of 107.7 t/h. © 2021, Central South University Press. All right reserved.