Research On Key Technologies Of Collaborative Mining Of Filling And Caving Mining At No.2 West Mining Area Of Longshou Mine

The No.2 west mining area of Longshou Mine is confronted with the dilemma of lower ore price and increased ground pressure with the increase of mining depth,so the change of mining method is considered.The sublevel caving method not only has the advantages of high efficiency and low cost,but also can effectively improve the stress state of surrounding rocks to complete the requirements of ground pressure control compare to the filling method.Therefore,the Longshou Mine decided to change downward horizontal cement paste filling method to sublevel caving method in upper part of the orebody in No.2 west mining area.In order to maintain stable productivity of mines in the transitional period,the No.2 west mining area will form a complicated mining situation,where there are three stopes with two different mining methods.And these three stopes are distributed at two levels.At this circumstance,several key technical problems need to be solved urgently.First,The sublevel caving method requires an caved overburden(caved waste capping)which need to safely and efficiently collapse the composite roof(referred to as composite roof)composed of nearly 30m cemented filler and about 100m upper overburden.Secondly,two adjacent stopes at the same level are produced by caving method and paste filling method respectively.The caving method requires roof collapse to form caved overburden,while the filling method requires roof stability.So how to coordinate the requirements of two mining methods for ground pressure control is very critical.Thirdly,how to conveniently and reliably evaluate the stability of the filling stopes at lower level to ensure the safety of filling stopes and caving stopes at upper level is another challenge.In order to solve the above technical problems,this paper mainly focuses on the following aspects:formation of caved overburden(caved waste capping)by caving the composite roof,synergetic mining safely and efficiently for filling and caving stopes,and determination of stability of filling stopes at the lower level,and has achieved certain research results.(1)Research on failure mechanism and falling law of composite roof.Cavitation analysis and calculation are carried out by studying mechanical and structural characteristics of composite roof.The influence of side pressure ratio,filler burial depth,filler strength,filler thickness and upper stratum inclination on the falling mechanism,mode and process of composite roof is studied by numerical simulation with DDA method.Meanwhile,the expanding sequence of filler exposure space and the influence of ore drawing control on the falling development of composite roof are studied,which provides theoretical basis and direction for formulating the scheme of overburden formation.(2)Scheme construction of overburden formed by falling composite roof in No.2 west mining area.According to the theoretical basis obtained above,the preliminary scheme of composite roof induced caving to form overburden is formed,with the emphasis on the dip angle of upper rock layer,mining sequence and ore control.Through on-site investigation,theoretical calculation and numerical simulation,the mechanism and mode of collapse of overlying composite roof in filling stope are studied,and field implementation schemes including determining reasonable initial mining position,slotting scheme,stope structure parameters,blasting parameters,mining sequence and mining control measures are constructed.(3)Research on spatio-temporal cooperative mining scheme of sublevel caving method and downward layered cemented filling in west No.2 mining area.The dynamic change law of secondary stress of surrounding rock under the influence of caving method is studied by means of the PFC,and a safe and efficient scheme of synergy between pillar-free sectional caving method and downward cemented filling method is put forward by controlling the mining sequence and progress according to the layout of sectional mining.(4)The stability of the roof of the stope with lower and middle filling method is studied,especially for the stability determination of large area adjacent non-continuous space which is easy to form when the downward cemented filling method is concentrated filling after several routes of mining,a method of transforming it into an equivalent goaf is put forward to determine the stability,and the method is tested and verified in the west No.2 mining area,with good results obtained.(5)The industrial test of co-mining of filling and caving in west No.2 mining area is carried out,and the development process of caving of composite roof is comprehensively monitored by on-site observation,microseismic monitoring technology and GNSS surface subsidence monitoring technology.The real-time and dynamic combination of monitoring results with underground mining conditions indicates that the analysis and research conclusions of caving characteristics and rules of composite roof in west No.2 mining area are in line with the actual situation.The validity of the proposed scheme for overburden formation and co-mining is also verified.Theoretical research and production practice show that the transition from cement paste filling method to sublevel caving method can be realized safely and efficiently by using the proposed scheme of induced caving of composite roof to form caved overburden.At the same time,reasonable adjustment of mining sequence and progress of caving and filling methods can effectively realize safe and efficient synergetic mining of the two mining methods,which provides a new way for the change of similar mining methods,underground collaborative mining and stability analysis of space.It is of great significance to promote the development of low-cost,safe and efficient mining technology and theory.