Research On The Reasonable Thickness And Stability Of The Top Pillar At The Boundary Of Open-pit Mining

In recent years,with the rapid development of the national economy,our country’s resource demand is getting larger and larger,and open-pit mining is widely used in mine production due to its large capacity,high efficiency and low cost;However,with the increasing depth of mining,the increasing slope height will also bring serious safety hazards to mine production,at the same time,open pit mining will be limited by resource conditions and economically reasonable stripping ratio.Therefore,many open-pit mines will be transferred to the underground after they have been mined to a certain depth.In the process of open-pit mining to underground mining,a part of the ore body is usually reserved at the bottom of open-pit mining and the top of underground mining,it is not used as a boundary pillar for isolation of open-pit mining and underground production;The boundary pillar can not only reduce the disturbance of underground mining to the open slope,but also confine the underground mining.However,if the thickness is too thin,the boundary pillar will be unstable;If the thickness is too thick,it will cause waste of mineral resources.Therefore,studying the reasonable thickness and stability of the boundary pillar has important theoretical and practical significance for mine production.In this paper,the open-pit to underground mining of the mine is the engineering background,through the various methods such as mechanical test,theoretical calculation and numerical simulation,the thickness of the boundary pillar in the transition period from open-pit to underground mining is studied,it provides a certain basis for the production of mines.The main research content of this paper includes the following aspects:(1)Firstly,through field investigation and data collection,we learned about the current mining situation and the basic conditions of open-pit mining to underground mining;At the same time,indoor mechanical experiments and direct shear tests are carried out for the main rock mass of the mine,and the rock mechanics parameters of the ore are determined by the Hoek-Brown criterion;(2)By analyzing the actual conditions of the mine,the solid-supported rectangular plate model is used as the mechanical model for calculating the thickness of the boundary pillar;The theoretical thickness of boundary pillar is calculated by the K.B.Rubenie equation,the thickness to span ratio method,the load transfer method,the method of structural mechanics and the Platts theory method,when the span of the stope is 35m,the thickness of boundary pillar were:52.52m、24.44m、26.88m、66.66m、21.95m.Then the regression analysis is carried out on the calculation results,and the relationship between the thickness of boundary pillar and the span of the stope is obtained.(3)Using FLAC~3DD numerical simulation software,the four schemes of the boundary pillar thickness are calculated separately.By analyzing the displacement,stress and plastic zone of the study area,the safe thickness of the boundary pillar is obtained,it should be 50 meters,and the thickness must be kept at least 30~35m.