Study On The Migration Law And Reasonable Thickness Of The Covering Layer Transferred From The Open To The Underground In Yanqianshan Iron Mine

With the consumption of shallow resources in opencast mining and the decline of economic benefit,the transition from opencast mining to underground mining has been carried out in all large mines at home and abroad.In this transition period,combined with the technical requirements of subsurface caving method without bottom pillar in underground mining,the bottom of the open pit should have a certain thickness of covering layer,so as to play a better condition of extrusion blasting and end ore drawing,windproof and stagnant water as well as the role of preventing rock burst.Once the overburden is too thin in the process of ore drawing,or even forms a funnel area,it will seriously threaten the underground safety production.Therefore,the study of the migration law and reasonable thickness of the overburden dispersion is very important to ensure the safe production of the mine during the transition period.In this paper,based on the engineering example of the Yanqianshan iron mine area,combining theoretical analysis with similar material test and numerical simulation,the migration law,structural characteristics and reasonable thickness of overburden dispersion in ore drawing are systematically studied.The main research contents are as follows:(1)According to the backfilling technology of the covering layer on site,the reasonable thickness of the covering layer of Yanqianshan iron mine should be no less than 30 m by theoretical calculation and analysis from the perspectives of ore drawing ellipsoid theory,ore drawing technology and landslide impact wave.(2)Combining the similarity theory and stope parameters in the mining area,the physical ore drawing experiment is conducted to reproduce the real ore drawing process.The flow law of ore and rock particles was summarized by observing the migration characteristics of the particles.According to the results of interface settlement of the covering layer under different thickness,combined with the functional requirements and economic indicators such as stagnant water and ablation of shock wave,the reasonable thickness of the covering layer of Yanqianshan iron mine is preliminarily analyzed..(3)Based on the analysis of physical experiments,the particle flow software PFC2D is used to build the mining model under different covering layer conditions.By monitoring the velocity of granular particles,the particle migration law summarized in the similar material experiment was verified,and the change of contact force chain in the covering layer in ore drawing was analyzed.Furthermore,the reasonable thickness of covering layer was optimized and analyzed through the change trend of the interface slope at the top of the covering layer with different thickness in the ore drawing simulation,and 35m is selected as the reasonable thickness of the covering layer of Yanqianshan iron mine...