Study Of Safety And Efficient Mining Technology For Medium-thick Steep And Fractured Phosphate Ore

The deposit of the Yongshaba middle-thick steep and fractured ore-body mine possesses some characteristics such as poor rockmass, deep-lying and high-value, belongs to difficult-to-mine ore-bodies. Five mining methods are selected for these ore-bodies, according to its technical condition and reality, techno-economics. Then, aiming at uncertain information of14evaluation factors in affecting mining methods the pros and cons, mining method optimization system based on unascertained mathematics theory was developed by means of VC++language. Yongshaba actual engineering project is calculated and analyzed by using the evaluation system, and the reasonable mining method for the manual roof downward staggered sublevel backfill is selected.Strictly according to design drawings, entity orebody model was established through MIDAS/GTS and CAD software, and it was imported into FALC3D finite difference software and entity orebody model numerical calculations were performed. The manual roof and stope structure parameter in final mining method were analyzed as an organic whole. Rock displacement field, stress field and the plastic zone variation rule during mining were simulated according to the different stopes parameters. The results show that the best stope structure parameter are20m stope’s height,20m stope’s span.Through engineering site applications, the final mining method proves that the suggested mining method can provides a safe working condition, increases the ore recovery ratio of mining significantly, reduces the ore dilution rate, fills mined-out-areas effectively, and reduces mining cost. Thus, the productive ability can be extended, and the mine’s comprehensive benefits can be obtained.Meantime, for the reason that the highly-stressed in-vein drill drift in the final mining method is severely destroyed by blasting vibration, the stability of the drill drift under dynamic loading is carried out with particle flow program PFC2D, according to the in-situ test data measured by Blastmate Ⅲ monitor instrument. Three different measured vibration velocity time-dependent curves are selected as blasting vibration input. And static calculation and dynamic calculation are analyzed respectively.The results shows that the variation rule of stress fields, displacement fields and crack fields in surrounding rock under blasting vibration will increase obviously compared with the static analysis. The higher rock vibration velocity, the more significant dynamic disturbance influences on the stress, displacement and crack quantities in surrounding rock of the tunnel. Several suggestions to avoid instability and subside of highly-stressed tunnel in-vein drill drift induced by blasting vibration are made.