| In view of the safety accidents caused by the existing mined-out areas in the open-pit mine,in order to clarify the mechanism of roof instability in the mined-out area and develop an economic and efficient treatment technology scheme.The paper relies on the national key R&D program "Disaster Mechanism and Synergistic Treatment Technology of Hidden Void Area in Large Open-pit Mine"(2016YFC0801603).Take Ansteel Group Mining Co.,Ltd.as an example.By means of theoretical analysis,laboratory test,similar model test and numerical simulation,the dynamic properties of surrounding rock in goaf and the influence of goaf morphology on damage mode were studied.The catastrophe mechanism of existing goaf instability is revealed.Combined with the measured data of the project,the blasting control scheme is formulated and industrial tests are carried out.The main research contents and results are as follows:(1)The existing goafs in open-pit mines are classified according to the field geological exploration data.According to the functional properties,the filling medium in the empty area and the distribution of the empty area,it is divided into three categories.The causes of different types of empty areas are analyzed.The damage failure of goaf roof is the quantitative representation of asymptotic damage.The macroscopic damage of goaf is analyzed from the microscopic point of view.Based on the plate theory,the mechanical stability of goaf roof is analyzed,and the boundary conditions of different working conditions are given.The correlation analysis of existing goaf with overlapping plane projection is carried out.The impact linkage effect of the collapse body in the upper goaf on the lower goaf is clarified.(2)The size effect of the specimen due to the length-diameter ratio affects the stress balance at both ends of the specimen under impact.Therefore,five kinds of length-diameter ratio(n=0.6,0.8,1.0,1.2,1.4)specimens were analyzed by SHPB optimization test under combined static load.The SHPB impact tests of surrounding rock specimens of goaf under different static loads were carried out.It is found that axial pressure and lateral confining pressure are applied to the specimen will affect the energy absorption ratio of the specimen under the same impact load.The introduction of secant modulus can well describe the plastic deformation of rock during the impact load.The pore changes of specimens before and after impact were detected by NMR.It is found that the lateral confining pressure has a certain hindering effect on the development of the specimen pores,and the impact strength and axial pressure play a promoting role.The influence of ground stress on surrounding rock damage is revealed to some extent.(3)According to the measured spatial profile shape of the goaf,the complex goaf is simplified based on the Monte Carlo method.Cuboid,prism,and cylinder are used as spatial reconstruction units.Based on the similarity theory analysis,combined with the measured surrounding rock properties of goaf,the similarity models of different goaf shapes were prepared.Blasting tests were carried out on the cured model specimens.The process of explosion load is analyzed by 3D-DIC technology.It is concluded that under the same load,the different shapes of the preset void area of the specimen show different damage modes.The spatial form has a direct influence on the stability of the surrounding rock medium.The cylindrical cavity has the strongest carrying capacity for explosive load,followed by the rectangular cavity and the triangular prism.According to the change of surface strain and displacement of the specimen,the structural tip of the empty area is determined as the response sensitive area,which provides a feasible idea for the optimization of the blasting scheme in engineering.(4)According to the numerical simulation results of specimen blasting,after the explosive explosion,the stress wave first produces a compression effect on the medium.When the stress wave meets the free surface,it will produce tension.The crack propagation tendency is related to the tip position of the void structure.The more concentrated the cusp structure,the more obvious the trend of crack penetration.The damage and failure of specimens after explosion load were quantitatively analyzed.The influence of goaf distribution form and shape structure on damage is obtained.(5)Based on the basic principle of three-dimensional DDA,the three-dimensional contact algebra calculation model and mechanical calculation model are introduced,to study the instability process of goaf roof under self-weight.The results show that when the roof is continuously broken and collapsed,the rock failure of the arch roof structure develops fastest.The water medium content in the empty area is different,and the influence degree of roof failure is different.The influence is most obvious when the internal water is filled.Different joint inclinations within the rock mass in the goaf have different promoting effects on roof instability.For the double goaf,the overlap degree of plane projection is different.The upper goaf has different effects on the roof stability of the lower goaf.Completely no projection overlapping mined-out area,the upper and lower mined-out areas have collapsed,which can be regarded as unrelated independent mined-out areas.According to the experimental research and numerical simulation results,the instability disaster mechanism of the existing goaf in open-pit mines is revealed.(6)According to the geological data of the engineering measured goaf,the technical scheme of blasting collapse control goaf is designed.The blasting vibration in the implementation process was monitored,and the phenomenon of excessive vibration under environmental protection requirements was analyzed.By adding auxiliary holes,optimizing delay time,and adjusting single hole dosage,the empty area control scheme is optimized.The blasting collapse treatment of goaf meeting the requirements of environmental protection was realized.Suggestions on blasting control and safety monitoring analysis of existing goaf are given. |
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