| In recent years,with the continuous promotion of the national green mining policy,the paste filling mining technology has become the preferred solution for mining due to its unique advantages in preventing surface subsidence and improving resource recovery rate.The drift filling method has always been the best choice for mining inclined and steeply inclined fractured ore bodies,but this layered,continuous,and small excavation mining process has limited production capacity.Therefore,in order to expand production capacity,the mine adopts a multi stage collaborative mining method,and the horizontal ore pillar is an inevitable product of the multi stage collaborative mining mode.At present,in the research on the stability and critical thickness of horizontal pillars both domestically and internationally,the importance of the true stress state and boundary conditions of horizontal pillars has been ignored,leading to a lack of reliable theoretical support in controlling the critical thickness of horizontal pillars.Excessive thickness of horizontal pillars can lead to resource waste,while too small thickness can affect the stability of the mining site.This article focuses on the stability of horizontal pillars and monitors the stress state of different middle filling bodies.Based on the theory of medium thick plates,a calculation model for the critical thickness of horizontal pillars formed by multi intermediate joint mining is constructed,and numerical simulation research is conducted on the 1319-1344 horizontal pillars of Huize lead-zinc mine.The main research content is as follows:(1)Selecting the filling ratio that is frequently used in mining filling,conducting mechanical basic tests on the filling body,and obtaining the mechanical parameters of the filling body under different mixing ratios.Based on the response surface method,the influence of the proportion of water quenched slag,water cement ratio,and lime sand ratio on the strength of the filling body in Huize lead-zinc mine was explored.Regression models for the 7d and 28d strength of the filling body were established.Through the analysis of the influence of material ratio on the strength of the filling body,it can be concluded that,The water cement ratio plays a decisive role in the middle and later stages of the strength growth of the filling body.The synergistic interaction between the water cement ratio and the ash sand ratio has the greatest impact on the strength of the 7d filling body,and the ash sand ratio and water quenched slag ratio have a significant impact on the strength growth of the 28d filling body.(2)A stress gauge was installed in different middle sections of the 1~#ore body in the mining plant to monitor the vertical and horizontal stresses in the filling body.According to the monitoring data,the stress values of the filling body in different middle sections basically vary around 1MPa,indicating a relatively stable stress.(3)Based on Mindlin’s theory of medium thick plates,a mechanical model of a horizontal mining pillar with four fixed edges was established under the combined action of multiple stress fields such as uniformly distributed overlying loads,self gravity,and bidirectional horizontal stress,with the bottom surface in a free state.The finite Fourier integral transformation method is used to solve and analyze the mechanical model of horizontal pillars.Based on the maximum tensile stress criterion,the critical thickness calculation model of horizontal pillars is constructed.The Control variates is used to explore the influence of stope span,stope length and overlying load strength on the critical thickness of horizontal pillars.(4)FLAC3D was used to simulate the process of joint mining of the upper and lower middle sections of the 1319-1344 horizontal ore pillar.When the thickness of the horizontal ore pillar decreased to 18m,a large plastic zone appeared inside the horizontal ore pillar.If further mining of the horizontal ore pillar occurred,a penetrating plastic zone would occur,forming a penetrating collapse.Determine the critical thickness of the horizontal pillar as 18m.The critical thickness calculation model of the horizontal ore pillar established in this article was used,combined with stress monitoring results,The calculated critical thickness of the horizontal pillar is 21.27m,which is almost consistent with the calculated critical thickness of the horizontal pillar in the double middle section joint mining. |
