Study On Mechanical Characteristics Of Ore Rock And Cemented Tailings Backfills Under Dynamic Loading And Engineering Applications

Filling(grouting)the complex broken rock and soil is a conventional reinforcement technology in geotechnical engineering,while the filling mining method used in mining engineering is an enlarged version of the filling reinforcement.This method is cleverly utilizing the load-bearing characteristics of the backfill.The replacement of the ore by the backfill is realized through the effective improvement of the stress state for the roof and floor of the stope.However,because mining engineering is a complex system integrating excavation,blasting and ore drawing,the ore rock mass and the backfill are in a complex dynamic environment.This is a technical problem for such mines to achieve the conversion of the bearing capacity between the two through engineering and technological methods.The solution of this problem can ensure mining safety and efficient production.This paper takes the filling mining method of Shandong Jinding Iron Mine as the research object.It combines the controlled blasting during secondary stoping and the spatial relationship between the ore rock mass and the backfill.Dynamic mechanical characteristics of the ore rock mass and the backfill are investigated to solve this problem.The following innovative results have been achieved:1.The relationship between the grade and dynamic behavior of ore rock is established qualitatively(partially quantitative),which provides an important theoretical and experimental basis for the parameters of blasting design and charging structure.Production blasting is closely related to the dynamic mechanical characteristics of the ore rock.In this paper,Split Hopkinson pressure bar(SHPB)test and high-speed digital image correlation(DIC)technology are used to study the dynamic mechanical characteristics and fracture characteristics of ore rock with varied grade.The curves of dynamic tensile strength-grade and fracture energy-grade provide an experimental basis for the determination of blasting designs and optimization of blasting parameters.Based on the microscopic images of mineral distribution and crack types in ore rock,the simulation technology of brittle rock is used to establish the strength equivalent models of ore rock with varied grade.A two-dimensional equivalent simulation method of SHPB Brazilian test is proposed and the meso-scale parameters of ore rock with varied grade are obtained.It provides a theoretical basis and parameters for further research on the mechanical response of the ore rock mass and the formation mechanism of fragments under dynamic loads.2.The dynamic relationship between the weakening effect on strength of the backfill and energy dissipation effect is established for the filling surface under dynamic load.The theoretical and experimental results can be used as an important basis for the damage assessment of the backfill under blasting load.The filling surface in large-volume backfill is caused by multiple fillings.Due to the frequent blasting in mines,the dynamic mechanical characteristics and fracture characteristics of backfill featuring filling surface were studied.Dynamic compressive strength and kinetic energy of fragments show that the filling surface has a significant weakening effect on the strength of the backfill.The ratio of the kinetic energy of the fragments to the absorbed energy of the specimen exceeds 20%,far exceeding the calculation result of the empirical formula.The curves of crack opening displacement-time show that the high kinetic energy of the fragments is related to the initial increase of speed caused by opening of filling surface in the early stage of the test.This process greatly weakens the overall strength and bearing capacity of the specimen featuring filling surface.In order to obtain the meso-scale parameters of the filling surface,SJM contact,which has been widely used in equivalent rock mass,is used to simulate the mechanical behavior of filling surface.This method provides a basis for the mechanical simulation of the large-volume backfill and the damage assessment of the backfill under dynamic load.3.A new design criterion for controlled blasting during secondary stoping and hole depth is proposed.According to this criterion,balance between production and mining safety can be effectively realized and the strength of the backfill is not significantly weakened.The controlled blasting adjacent to backfill(secondary stope)is a technical problem faced by Jinding Iron Mine in completing the task of increasing production.Based on the dynamic tests and numerical simulation of ore rock and backfill,this paper establishes an ore rock mass-backfill model under dynamic load and uses the density-based clustering method to quantitatively describe the damage of the backfill under dynamic load.Under the consideration of the economic-safety balance,a comprehensive evaluation model is established in combination with the response surface analysis.The interaction between the grade,the distance between bottom of the blast hole and the backfill and the age of the backfill is investigated by significance test.Parameters and design criteria of controlled blasting during secondary stoping are proposed considering the value of ore rock and mining safety.Besides controlling the damage of the backfill,it also achieves the goal of recovering high-grade ore rock and reducing the loss of ore rock.The innovative results obtained in this paper have been successfully applied and promoted in Shandong Jinding Iron Mine,and have obtained positive effects.