Study On The Formation Mechanism And Numerical Simulation Of A Surface Collapse Pit In A Mine In Northwest Yunna

Relying on a certain copper mine,this paper uses a combination of theoretical analysis,indoor simulation test and numerical simulation test to conduct a special study on the problem of surface deformation and collapse.Through theoretical analysis,the conditions for the formation of collapse pits on the surface are expounded from different angles.Through indoor simulation tests,the relationship between mining and the formation of collapse pits on the surface is analyzed,and the mechanism of surface deformation and collapse is studied.At the same time,combined with numerical simulation tests,the results of indoor simulation tests are verified,and new test conditions are established to study the mechanism of surface deformation and collapse,which makes up for the shortcomings of indoor tests.The main research results are as follows:(1)In the naturally loose and air-dried state,the apparent density of moraine soil is greater than the apparent density of crushed ore.(2)In the naturally loose and air-dried state,there are no large voids formed between the moraine soils,or the lower ore,or the moraine soil and the lower ore.That means there is no “hard shell layer” formed in the middle.(3)When the copper mine adopts the natural caving method for mining,with the progress of mining activities,collapse pits will definitely form on the surface.And the time to form a surface collapse pit has a certain time relationship with the thickness of the formation: the thicker the formation,the longer it takes to form a surface collapse pit;the thinner the formation,the shorter the time required to form a surface collapse pit.(4)With the gradual release of the surface moraine soil and the lower ore,a more regular discharge funnel will be formed in the upper part of the moraine soil,and the discharge funnel will always exist during the release of the ore and the surface moraine soil.(5)According to this process,it shows that at the beginning,only the lower ore was released,and the upper moraine soil was not released,and the lower ore was released in the process with the largest amount and the fastest speed.When it is close to the middle of the total ore release time,the moraine soil begins to be released,and the number of releases continues to increase,and the speed continues to increase.In the late stage of the total ore release time,the speed of ore release is constantly decreasing,and the speed of moraine soil release is constantly increasing and has been maintained at a high speed.And then it will enter the ore layer during the ore release process and be released together with the ore release,and finally the surface moraine soil precedes the lower part.The ore release is completed.(7)In the process of forming surface collapse pits caused by the falling of the upper moraine soil,the formation rate of collapse pits is showing a trend of accelerating,and with the larger the amount of ore released,the more favorable the formation of surface collapse pits becomes.(8)Through indoor simulation tests,it is concluded that in the natural loose state,the natural inclination of the surface collapse range caused by the release of ore is 65°to 72°.Through numerical simulation tests,it is concluded that in the natural loose state,the natural inclination of the surface collapse range caused by the release of ore is 66°.According to the overall topography of the mining area,the topography of the area generally tilts to the west,with low west and high east.Therefore,when the surface collapse pit is formed,the collapse pit is also low west and high east as a whole.