Study On The Thickness Of The Top Pillar Of The Open-pit To Underground Mining In The West Of Guizhou

Open pit mining plays an important role in the development and utilization of mineral resources,however,With the development of open pit mine,the mining depth is deepening,and the recovery cost of the ton ore is gradually increasing,the height of the open pit slope is increasing at the same time,and the safety problem is prominent;A series of problems,such as open air transportation,high and steep slope,difficulty of drainage,deep pit ventilation and so on,threaten the normal production of the mine and force the mine to renew the mining technology.Under such a background,the mining method of open pit to underground mining came into being;However,the new technical problems are coming:? Blasting in the open pit will cause some damage to the underground roadway and stope,there should be enough distance between the underground engineering and the open pit bottom;?The normal production and safety of Open pit mining are under the influence of underground engineering work during the transition period,so it is necessary to leaving the boundary pillar and room pillar between open pit and underground stope;?Underground mined out area will affect the safety of open pit slope and production operation;?Open pit water flooding into the underground,there will be some waterproof measures in the open pit and underground communication roadways or goaf to prevent the sudden influx of sediment water.This paper focuses on the specific project profiles of Yunnan western Precious metal ore open pit to underground mining,take the problem of the thickness of boundary pillar in transition period of open pit to underground mining into research,through the research work,we can find out the method which is suitable for the determination of the thickness of the top pillar,providing some basis for the production practice of underground mining.This paper mainly includes the following aspects:(1)To understand the basic situation of underground mining to underground mining,the mine geological conditions and ore rock conditions through the field investigation and data collection;According to the three kinds of main lithology of this study,the field sampling,sample preparation and indoor rock mechanics experiment were carried out,using the hoek-brown law to solve the porphyry,limestone and rock mechanical parameters of rock mass.(2)The main failure modes of the boundary pillar are discussed,that is,the tensile failure,the collapse damage and the cumulative damage;The internal and external factors that affect the stability of the top pillar are analyzed;At the same time,according to the basic knowledge of elastic-plastic mechanics and the geological condition of the mine,the mechanical model of the boundary pillar is established which is called Clamped rectangular plate,and the mechanical analysis of the model is carried out.(3)Calculating boundary pillar thickness of the Precious metal ore by using the load transfer method,line thickness to span ratio method,structural mechanics simplified beam method,the method of structural mechanics,the Lou Beneit formula,When the stope span is 11.94m,the algorithms under the thickness of boundary pillar were:12.87m,8.36m,16.79m,60.05m,4.17m;Get the relationship between the boundary roof pillar thickness and span of stope by regression analysis.(4)Simulation analysis is carried out by using FLAC3D numerical simulation software(The working condition is the combination of 40 meters thickness and span under different calculation methods);Simplified beam method of structural mechanics is suitable for the Precious metal ore open-pit to underground mining transition boundary pillar thickness calculating.(5)Simulation analysis shows that the minimum thickness of the top pillar is 45 meters by using FLAC3D numerical simulation software;The influence of different mining sequence on the boundary pillar is studied in the determination of the minimum safety thickness,finally,it is concluded that the disturbance of the boundary pillar is smaller when using the way that exploit from the center to the sides of the mining method,so suggest the mine take this Stopping way.