| Block caving refers to the mining method that uses the stress redistribution caused by undercutting to induce ore caving in rock mass.The mining method is especially suitable for these low-grade mines with thick ore bodies.The mining method can significantly improve the mining efficiency,reduce the mining cost,improve the production intensity,and improve the market competitiveness of mine operators.This mining method has advanced production technology and certain scale benefit,but its advantages and disadvantages are also very obvious,the application of block caving needs a high level of production management.In the process of block caving,before the cave break through the surface,the ore caved under the condition of open field.If the withdrawn is too fast,there will be a large airgap between the cave back and the caved ore pile.Once the crown pillar fails in a large range,it will produce a destructive shock wave,which will damage the underground working face;at the same time,the extraction level withdrawing activity will produce the redistribution of the stress,which will reduce the strength of the extraction level structure.After the cave break through the surface,it may cause large-scale collapse of the surface,which is easy to cause geological disasters such as surface landslides and may lead to difficulties in later ore extraction.The research topic of this paper comes from Pulang copper mine in the hinterland of Diqing plateau in Yunnan Province.It is a super large porphyry copper polymetallic mine discovered in 1999 in China.The ore body is thick but relatively broken,with inclined attitude,staggered faults and developed joint fissures,which is more suitable for large-scale mining with block caving method.Block caving mining in Pulang copper mine is faced with many problems,such as the uncertain development behavior and state of rock mass caving,and the development process of surface subsidence and collapse is difficult to accurately evaluate.Therefore,it is necessary to interpret the data of the whole evolution process of block caving through engineering rock mass monitoring technology.This paper analyzes and summarizes the caving mechanism and specific monitoring requirements of the caving development process of Pulang copper mine,develops and constructs a multi-scale,all time and space integrated online monitoring system for the block caving development process of Pulang copper mine,realizes the multi-scale data representation of the block caving development and evolution process in the multi-dimensional space,and studies the temporal and spatial evolution law of block caving based on the multi-scale data.The refined data representation of the whole time-space evolution process of block caving development,and the basic law of the whole time-space evolution of the block caving of Pulang copper mine are revealed by the actual quantitative data.The main research contents of each part of this paper are as follows:(1)Study on multi-scale and full space-time monitoring system for the development process of block caving in Pulang copper mine.According to the investigation of the monitoring and observation methods for the mining process of the block caving at home and abroad,the caving mechanism of each stage of the development and evolution of the block caving of the Pulang copper mine is analyzed in combination with the geological conditions and the characteristics of the production process.The control mechanisms of the block caving in Pulang copper mine is stress caving induced by undercutting,gravity caving and fault induced caving.According to the monitoring requirements for the development process of block caving and the requirements for the monitoring system,this paper puts forward the targeted monitoring technology and corresponding equipment,and constructs the multi-scale full time and space monitoring system framework for the development process of block caving.The system lays a solid foundation for the follow-up study of the temporal and spatial variation rules of block caving development.(2)Study on the law of caving development of overlying rock mass.Based on the data of multi-scale comprehensive monitoring system,the temporal and spatial evolution law of overlying rock mass caving development in Pulang copper mine is analyzed.Based on the time series of the development trend of cave back based on the accumulated apparent volume and energy index of microseismic events in the large-scale rock mass caving space,this paper analyzes and delineates the stage characteristic zoning of rock masses such as the yield zone,the seismogenic zone and the elastic zone.Based on the monitoring data of open hole,the average caving speed of cave back predicted by the pre mining numerical value is modified,and the conclusion about cave back shape of numerical simulation before mining is verified by TDR monitoring data.By analyzing the temporal and spatial distribution of microseismic events around the fault,the influence of fault activation on the regional stability of key facilities near the fault is evaluated.The block caving process of Pulang copper mine is divided into initial undercutting stage,initial caving stage,caving development stage and caving break through the surface.It is pointed out that the development process of the block caving in Pulang copper mine is controlled by the disturbance of undercutting,the induction of fault activation,and the rock mass conditions of the first mining area.The general law of the evolution process of the block caving of overlying rock mass of Pulang copper mine is concluded.(3)Study on the law of surface subsidence in block caving mining.By means of time series analysis of monitoring data,the evolution law of surface subsidence of Pulang copper mine was studied.Combined with the geological conditions of the first mining area and other monitoring data,this paper analyzed the causes of the surface subsidence pit in the early period of undercutting and the small skylight group at the bottom of the pit after the overall collapse of the surface,delineates the scope of the surface subsidence by using the monitoring data.This paper analyzed the statistical combination of the surface subsidence area and undercut footprint,judges the development trend of the surface subsidence area.The monitored subsidence data in each area was compared with the ore drawing height calculated by the drawing management software,which realizes the quantitative evaluation of the rock mass caving in the three-dimensional space and provides data guidance for the adjustment of the undercutting and drawing strategies.The empirical method is used to estimate the cave angle in Pulang copper mine,and the reason for the large current caved angle is analyzed.Based on the monitoring data,the influence of the production draw on the surface subsidence is analyzed.The evolution of surface subsidence in Pulang copper mine can be divided into five stages: subsidence preparation,surface continuous & discontinuous subsidence,regional collapse appearance,initial break through the surface and continuous expansion of collapse scope.It is pointed out that the surface subsidence of Pulang copper mine are controlled by many factors,such as the action of fault fracture zone,the action of undercutting and ore drawing,the action of surface topography and the action of surface water.The scope of surface subsidence shows a linear relationship with the development of undercutting footprint,which can be predicted and judged according to the fitting linear relationship between the surface subsidence area and undercutting footprint.Based on the analysis of multi-scale monitoring data obtained from continuous monitoring for more than two years in Pulang copper mine,the general law of spatial and temporal evolution of block caving development is revealed,which provides a scientific basis for the adjustment of production process parameters and a guarantee for the safe and efficient mining of block caving.The research results of this paper will provide reference for many open-pit to underground mines and large-scale and efficient development and utilization of low-grade thick ore bodies in China. |
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