| In recent years,the rapid development of the economy has led to an increasing demand for steel production in China,while the low per capita reserves,poor quality and low grade of iron ore resources have forced us to rely heavily on imports.This is a situation of high dependence on foreign countries.It limits the safety of China's steel industry and the healthy development of the national economy.How to use scientific and technological innovation to achieve safe and efficient mining of iron ore resources,especially rich iron ore,which is relatively scarce in reserves,will have important strategic and practical significance for establishing an orderly environment for the development of the steel industry and promoting the well-being of people in society.At present,as China's iron ore mining is gradually transferred from the open air to the underground,the pillarless sublevel caving method has been widely used due to its remarkable advantages.The sublevel caving method without pillars is to use the fan-shaped upper-middle-hole blasting to recover the ore mining under the condition of loose rock stratum.The blasting effect has a significant impact on the recovery rate.The sub-column sublevel caving method has high ore recovery rate,low cost and good security.However,in the actual blasting construction,there will be major problems such as high ore depletion rate,high ceiling,large block rate and large consumption of explosives.The traditional selection of blasting parameters is mainly engineering analogy method.experience method,etc.,mainly relying on the experience of field technicians.The choice of parameters is relatively random,lack of theoretical and scientific basis,and has a greater impact on sublevel caving blasting recovery without bottom column.In view of the above key technical problems of iron ore mining,the rock blasting of rich iron ore is taken as the research object,and the blasting damage of mineral rock with different charging structures is revealed by means of physico-physical experiments,blasting model experiments,SEM,CT scanning and numerical simulation.The optimization technology and method of fan-shaped deep hole blasting parameters are proposed.Based on the theoretical research results and artificial intelligence technology,an intelligent design system for blasting parameters of sub-column sublevel caving method in Futie Mine is developed,and the iron-rich ore fan shape is realized.The deep hole blasting scheme has scientific and reasonable decision-making,which provides a new technical approach for the mining of metal mines in China without bottom-bottom collapse.(1)Laboratory and field experiments were carried out to study the mechanical properties and explosiveness of iron-rich ores.Based on the uniaxial compression and Brazilian disc splitting experiments,the mechanical properties of iron ore-rich rock under static conditions were studied.The physical and mechanical parameters and mechanical failure characteristics of rock under static force were obtained.The dynamic mechanical properties of rock under impact load were obtained by compression and splitting experiments based on the split SHPB experimental system.The dynamic mechanical properties of rock under impact load were obtained based on Livingston blasting.According to the funnel theory,field blasting funnel test was carried out,and the blastability of iron ore-rich rocks was evaluated.According to the evaluation index,the rock blastability in field test was difficult to explode.The above research results provide theoretical basis for blasting damage experiment,numerical simulation and optimization of blasting parameters of rich iron ore.(2)The blasting damage mechanism of rich iron ore was studied.The rich iron ore collected in the field was processed into D=50 mm in diameter and H=100 mm in height.The blasting experiment was carried out in a special device with passive confining pressure.The damage degree is calculated by CT scanning,three-dimensional reconstruction and fractal dimension,and the failure laws of three different charge structures proposed in this paper are compared and analyzed.?Blasting experiments were carried out on rich iron ore under different plugging conditions.Three-dimensional reconstruction and three-dimensional damage assessment were carried out on the specimens.It was found that the damage values of three-dimensional bodies were 0.82 and 0.61 under plugging/non-plugging conditions,and the damage of three-dimensional bodies without plugging structure was 25%lower than that of plugging structure.Compared with the actual blasting effect,under the condition of complete blockage,the iron ore sample produces multiple fissures,which reduces the probability of the occurrence of large blasting blocks,and is more favorable for ore body breakage.?The structure of radial uncoupled charge blasting was studied experimentally,and the damage degree of specimens under six different radial uncoupled charge conditions was compared and analyzed.From the relationship curve between uncoupling coefficient and damage degree,it is found that when uncoupling coefficient is between 1.2 and 1.5,there exists a distinct sudden descent section.It can be inferred that there exists an "optimal uncoupling coefficient range" in this area,which can avoid over-fragmentation of ore body,effectively destroy rock mass and control blasting bulk ratio,in order to achieve the best blasting effect.?The sectional Caving Blasting without sill pillars uses sector holes to arrange blasting holes,and the distance between the bottom holes is 6-8 times that between the holes.Based on this,a blasting method of variable line charge density is proposed.It is found that the local damage degree is 0.81 when the uncoupling coefficient of the density section of the Variable-line charge is 1.5.By comparing and analyzing the overall damage,the overall damage degree and explosive quantity are reduced by 6.8%and 20%respectively by using the local Variable-line charge structure compared with the fully coupled charge blasting.It can be seen that the change of linear charge density can meet the demand of ore body breakage while reducing the explosive quantity(the damage degree is greater than 0.8 and the rock mass is considered to be sufficiently broken).(3)Based on the parameters and model experimental conclusions obtained from rock mechanics experiments,the numerical simulation of blasting with different charge structures in sublevel caving method without sill pillar was carried out by using LS-DYNA software,and the failure law of rock blasting under the condition of the change of charge structure was studied.?The numerical simulation of 75 mm borehole coupling blasting and variable charge density blasting is carried out.It is found that the breaking range of the borehole near the borehole is approximately 7 times the borehole diameter under the condition of single borehole coupling charge blasting.The contrast analysis shows that the strength of the effective stress field in the blasted rock mass decreases significantly after using variable linear charge density,and the structure of the stress wave front changes.However,the overlapping effect of two series of stress waves makes the peak value of the secondary stress increase sharply.Obviously,the simultaneous blasting with two-stage variable linear density charge structure can achieve the same blasting effect as the single-point initiation with coupling charge.?The full-face Blasting simulation of fan-shaped holes by sublevel caving without pillars was carried out with 75 mm boreholes.The results show that the damage rule around the borehole is approximately the same as that around the single borehole blasting in the whole length range from bottom to 2/3.The diameter of the borehole is about 7 times.At the top of the borehole,the superposition of stress wave intensifies the rock mass breakage around the borehole.It can be predicted that the occurrence area of large ore body is at the bottom of the borehole,and the ore body at the mouth will be seriously broken.By means of numerical simulation,the evolution and superposition law of stress field in Sublevel caving blasting without sill pillar is obtained,which provides theoretical support for intelligent design of blasting system and field test.(4)Based on the above research results,blasting knowledge rules are formed by integrating blasting safety norms and blasting expertise,and a knowledge base of blasting experts for sublevel caving without sill pillars is established.The blasting scheme reasoning engine is constructed by forward reasoning,tree reasoning strategy and SQLServer database technology.An automatic drawing subsystem of sectoral borehole profile is developed by using the secondary development technology of Atuo CAD.By using the hierarchical and modular overall system structure and object-oriented programming technology,an intelligent blasting design system for sublevel caving without sill pillar in rich iron ore was developed.An integrated blasting reasoning and graphics rendering technology platform for non-pillar sublevel caving of rich iron ore is constructed,and scientific and rational decision-making of fan-shaped medium-deep hole blasting scheme for rich iron ore is realized.Applying the system to the field,the blasting effect shows that the reasoning scheme of the system can reduce the ore bulk rate and the explosive consumption to a certain extent compared with the ordinary blasting. |
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