Optimization Study On Thickness Of Natural Isolation Pillar From Open Pit To Underground Pit

With the continuous development of shallow mineral resources,many mines are facing the transition from open-pit to underground mining.At this time,the mines will set up a certain thickness of isolation pillar to ensure the safety of underground mining.A properly sized isolation pillar not only maintains the safety of the stope,but also helps maintain the stability of the slope.According to the geological conditions of the Guilaizhuang gold deposit,this paper uses mechanized upward horizontal cut and fill method for the inclined thick and unstable solid ore body.The section of No.Ⅱ exploration line was selected as the experimental prototype,and large scale similar material experiments and numerical simulation studies were carried out in the laboratory.The stability of the isolated pillars and slopes under different thickness conditions was discussed,and the isolated pillars were optimized and analyzed.Large scale similar material experiment and numerical simulation were used to excavate.the isolation pillar model with different thickness reserved.The stability of isolation pillars and slope was discussed.The main research contents are as follows:1.According to the survey of the geological conditions of the Guilaizhuang gold deposit,KB Rubenieit theory,thickness-span ratio method,engineering calculation method,and empirical analogy are used to calculate the thickness of the isolated ore pillars under different spatial spans.With a span of 24m,the theoretical thickness of the isolated pillar should be greater than 10m;2.According to the similar material selection principle and the advantages and disadvantages between various raw materials,the river sand and barite powder are selected as aggregates,paraffin is used as cementing agent.Develop standard parts of similar materials between different proportions,test their physical parameters in the laboratory,and determine the material proportion of large-scale similar material experiments based on the similarity theoretical criteria and the original rock mechanics parameters;3.The large scale similar material experiment was performed using the determined ratio,and the underground mining and filling process was simulated under different thicknesses of the isolated pillars.The XJTUDP three-dimensional optical photogrammetry system was used to monitor the displacement field of the isolated pillars and slopes during the mining process.Analyze safety issues in isolated pillars;4.The FLAC software was used to simulate the displacement changes of the isolated pillars and slopes with the ore body mining under different thicknesses of the isolated pillars to verify the experimental results of large similar materials.According to the evaluation index of the plastic zone volume,slope safety factor,and surface slope rate of the isolated mine pillar under different scenarios,the use scheme of the return to open-air to underground isolated mine pillar is recommended.