Research On The Thickness Of Boundary Pillar Of Transition From Open Pit To Underground Mine

In order to keep the stability of production and less fluctuation, during the transition period from open pit to underground mine, steeply inclined ore body sometimes needs to be simultaneously mined in vertical direction. To solve the interaction problem between open pit and underground mine, people generally adopt open stope method which maintain a boundary pillar between the bottom of open-pit and the room top of the first underground middle section. So, it is very important to make sure a sound thickness of boundary pillar. In actual work, most mines adopt their boundary pillar's thickness by engineering analogy method—consulting the experiences of similar mine. To meet the demand of safety production, the boundary pillar is relatively thick. However, it arouses severe waste of resource and depression of economic profits. Therefore, there is a defect in adopting boundary pillar's thickness in this way. By now, no one has studied boundary pillar by the technology of numerical simulation.In consideration of such concerns, this paper put forwards the research of adopting reasonable thickness of boundary pillar. Combined with the actual production of Shirengou Iron Mine, using numerical simulation technology and ANSYS—finite element software, it applies step excavation simulation in the first mining district and analyzes the variation regularity of stress in wall rock and boundary pillar. It also analyses and compares the simulative outcome under variable pillar's thickness and room's parameters at the angle of stability. At the same time, this paper discusses the feasibility of changeable thickness pillar, develops the thinking for selection of boundary pillar's thickness, gains the conclusion that it is feasible under the condition of sound stope parameters and small changeable thickness of boundary pillar. Making use of fuzzy theory, it evaluates the boundary pillar from the angles of stability and economy. At last, we gained the conclusion that when the thickness of boundary pillar is 15m and the width of interval pillar is 6m, we can furthest reclaim resource.This study is practically significant for increasing economic and social profits of mine.