Research On Accumulative Damage Rule Of Stoping Mid-deep Difficult-to-produce Iron Ore Based On Improved Damage Constitutive Model

With the stoping of the difficult-to-produce reserved mineral resources in the underground mines being carried forward continuously,the issue of accumulative damage of the rock mass in the stope caused by multiple blasts has become increasingly prominent.And the high ground stress in mid-deep will affect the accumulative damage of the surrounding rock in the stope caused by multiple blasts further,therefore the stability of mined-out area will decrease,which will endanger the safety of construction crew working in mined-out area and equipments and affect the stope construction progress.Therefore,based on the improved damage constitutive model,this paper uses the stope blasting project of the safety pillars in the western district of Chengchao Iron Mine as the research object to compare and elect the best stoping method and the best stoping sequence,analyze the accumulative damage law of rock mass in the complex mined-out area caused by multiple stope blasts and discuss the accumulative damage law under the static-dynamic coupling loading with different ground stress,then offer guidance for the actual stope blasting project on the basis of the accumulative damage law.The main research contents and conclusions of this paper are as follows:(1)Most existing damage constitutive model can’t reflect the high strain rate and the damage degree during the rock mass blast simultaneously,so this paper forms the improved tensile-compressive shear damage constitutive model based on the damage variables,then uses the partition theory result of rock blasting damage and the field test result to verify the model.(2)Based on the user-defined damage constitutive model and recovering quantity,assessing the stability of the mine area under different stoping methods from the point of the damage of the rock in the mine area,and electing the best stoping methods with the economy principle,then electing the best stoping sequence,by using the accumulative damage condition of the rock in the mine area under multiple multiple blasting comprehensively.(3)Through analyzing the influence of multiple blasts on the rock mass damage,the law of the influence of multiple blasts in the complex mined-out area on the accumulative damage of rock mass of the moderate or far field in the stope and the highly damaged area that needs to be monitored or supported have been obtained,and according to the two factors which affect the accumulative damage greatly,the method of drilling holes between the protection-needed area and explosion center has been offered to reduce the accumulative damage.(4)Under the static-dynamic coupling loading,the total rock mass damaged volume of the stope and the rock mass damage volume of the cloze zone decrease primarily and then increase with the ground stress increasing all the way,but the effect of the accumulative damage of the rock mass in moderate or far field becomes more significant with the ground increasing all the way.Therefore,in the actual construction,actions that suit local circumstances should be taken i.e.the parameters of charge amount per delay interval、excavation footage and so on should be adjusted to different buried depth,the blast design also should be optimized to minimize the influence of ground stress on the rock mass accumulative damage caused by multiple blasts.(5)When the ground stress increases continuously,because the strengthening of the clamping force of the rock mass will repress the damage growing up and the ground stress redistribution will aggravate the damage growing up,the accumulative damage increment of the rock mass caused by the explosive load decreases primarily and then increases.And after the ground stress increases to a certain extent,the ground stress multiple redistributions will be the leading factor which affects the rock mass accumulative damage increment caused by explosion load,at this moment,in order to ensure the stability of mined-out area,the amount of ore per blasting mining should be controlled strictly.