| The large-scale mining exploitation has destroyed environment gravely,resulting in large areas of goaves,accumulation of tailings waste,emergence of frequent geologic disaster and destruction of physiognomy sight.Such problems severely restrict the sustainable development and utilization of mineral resources as well as the healthy development of the mining industry.The backfilling mining method fills underground mined-out areas with solid waste,which achieves the purpose of supporting surrounding rock and controlling surface subsidence.It has the dual roles on protecting the environment and increasing the utilization rate of ore.At present,the main research directions for underground filling include: the development of low-cost and high-strength cemented filling materials,realizing cemented filling of solid wastes such as tailings,and solving the supporting problem of unstable failure in large-scale continuous mined-out areas.This is also a key technology that needs to be studied urgently to realize the green mining and sustainable development of mineral resources.In this paper,for improving stability of large-scale goaves,theoretical analysis,laboratory experiments,numerical simulations,and on-site monitoring method were used to study the microstructure,macroscopical mechanical properties of the new whole tailing cemented backfilling materials.Afterwards,new strength models for the upward horizontal slice filling body were developed.The synergistic support theory was proposed to realize the matching among the filling body,surrounding rock and pointed pillars.The main research work and conclusions are as follows:(1)The paper tested the microstructure characteristics and macro-mechanical properties of whole tailing cemented backfilling materials with different cement-tailings ratio and different curing ages.The pore morphology of the backfilling materials was quantitatively revealed.Test results have shown that under different conditions,the filling body strength changes with the microstructure characteristics.The conclusions are as follows: the cement-tailings ratio decreases,the porosity increases,the degree of homogenization decreaces,the pore shape becomes narrower and longer,the complexity increases,the ordering and compactness reduce,the strength of cemented filling body decreases;with an increase in curing age,the porosity and average pore area decrease,the proportion of micropores increases,the pore shape becomes smoother,the complexity reduces,the orientation enhances,and the filling body strength increases.(2)Compressive strength tests have tested different proportions of backfilling materials.From the macroscopic point of view,the relations of the backfills' strength with slurry concentration,cement-tailings ratio and curing age,together with the sensitivity of the backfills' strength to three main factors were studied.There is a certain non-linear function relationship between the backfills' strength and the three factors.The sensitivity of the three is: cement-tailings ratio> curing age> slurry concentration.At the same time,the high-precision GA-SVR backfill strength prediction model for multi-scale influencing factors(from microscopic to macroscopic)was constructed,which was superior to BP neural network and polynomial regression.The layered backfill body is divided into two parts,the cemented layer and the lower tailing filling body.The mechanical models of the cemented layer and lower tailing filling body in inclined deposit mining were established respectively.The formulas for calculating the strength of the cemented layer and lower tailing filling body were derived.Therefore,the filling ratio can be optimized according to the different filling strength requirements in the mined-out areas.(3)Based on the complex variable function method,the stress calculation formulas for the surrounding rock mass in the upward slice filling mining were deduced.The law of deformation and failure of the surrounding rock were revealed as the filling height changed and the working face moved.The theory of mining space movement was proposed,the deformation characteristics of the surrounding rock were analyzed by numerical simulation techniques.Features include: increasing filling height,deformation law of surrounding rock in single and triple stopes and different failure modes.The tensile stress and subsidence of roof are continuously reduced,the floor heave is reduced,and the lateral displacement of surrounding rock of two sides increases.The stress concentration in the corners is reduced and the stability is improved for a single stope.There is a “group effect” in the triple-span stopes: the displacement first rises and then falls,the maximum deformation moment occurs in the early production period,and the most dangerous location is the middle part,which needs attention.The stability control measures of surrounding rock were proposed: roof support,span reduction by pillars,parameter design of backfill,reinforcement of wall rock,pressure relief mining.(4)The synergistic support system including filling body,surrounding rock and pointed pillars was proposed on the basis of the support mechanism.The theoretical analysis and numerical simulation were combined to reveal the mutual influences and synergistic support mechanism of the three supporting units,and the phased instability criterions were developed accordingly.The support action among three units was not simply superimposed,the reasonable choice for parameters took advantage of all units,provided complementary functions in strength,stiffness and materials.The overall performance of the support system was improved,the surrounding rock deformation was coordinated to ensure the safety and stability of large-scale mined-out areas.(5)The mechanical analysis model for irregular pillar under filling condition was established,and a FEM numerical model of horizontal pillar that used contact element was presented to study the effect of the pillar thickness on maximum principal stress and deflection.The maximal principal stress and deflection of pillars had a clear decreasing trend as the thickness increases and followed a power function.Based on the maximal tension stress theory,the critical safety thicknesses with different safety factors were calculated,and the calculated result was keeping with the actuality of engineering.(6)The innovative and optimized filling mining technology and collaborative control technology were applied to the mine engineering example.The surface movement monitoring system and a numerical prediction model has been established to study the ground movement and deformation law.The surface deformation of steep-inclined ore body had the following characteristics: asymmetry,damage location concentrated,and difficult to extend damage scope.Based on the analytic hierarchy process,a reliability assessment system of surface movement prevention and control technology for large-scale filling and mining was established.The reliability score was 80.3534,more reliably,and the rationality of improving reliability of surface subsidence prevention and control technology was proposed.For backfill mining design,the cement-tailings ratio and slurry concentration can be appropriately increased by optimizing the filling process and filling ratio.The mine can be operated with backfilling simultaneously and the filling parameters can be monitored on time. |
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