Study On Long-term Stability Of Paste Backfill Mining Under Tunnel

With the development of traffic construction industry and mining industry in China,there are more and more problems in the mine or goaf under tunnels.The continuous construction of highways,railways and subway and other transportation facilities often inevitably cross the the mine goaf,and the problem of mine under tunnels also occurs from time to time.Therefore,how to deal with the relationship between goaf and tunnel,not only to ensure the safety of tunnel,but also to exploit useful minerals as much as possible,has become a common problem faced by tunnel engineers and mine engineers.In this paper,MIDAS GTS was used to carry out numerical simulation of full subsidence mining and backfill mining under the tunnel.The stability of tunnel support structure and surrounding rock under the condition of full subsidence mining and backfill mining was analyzed.The distribution law of stress field and displacement field of tunnel surrounding rock affected by mining was explored.The evolution law of physical,mechanical properties and microstructure of geopolymer cemented coal gangue-fly ash backfill?GCGFB?after corrosion during backfill mining under tunnel was analyzed,and the influence of corrosion on the stability of surrounding rock of tunnel under corrosive environment was studied.Research results show that:?1?After full subsidence mining,the whole tunnel structure is subjected to large bending moment and axial force,two sides of the tunnel structure are subjected to tensile stress,sedimentation value of tunnel surrounding rock reaches 20.8mm.After backfill mining,the tensile stress value of tunnel is reduced.Compared with the unfilled goaf,the subsidence value of tunnel surrounding rock is reduced by 4mm,subsidence reduction effect is obvious.?2?After GCGFB was subjected to long-term action by NaCl and Na₂SO₄ corrosion solution,its uniaxial compressive strength,mass and relative dynamic elastic modulus all increased first and then decreased.GCGFB in MgCl₂ solution was cross-corroded by Mg²⁺and Cl^-,its strength,relative dynamic elastic modulus and mass decreased with the increase of corrosion time,and the loss rate was largest.Type of solution had the greatest influence on the strength.The influence of concentration and temperature on the strength of the corrosion process were not much different,the concentration was greater than the influence of temperature on the strength of GCGFB.?3?SEM,EDS and XRD analysis showed that after GCGFB was immersed in MgCl₂ solution,chloride crystals appeared inside.Magnesium ions in MgCl₂ solution could replace calcium ions in GCGFB to form Mg?OH?₂ without cementing ability,the structure of GCGFB was more loose,thus MgCl₂ solution had cross-erosion effect on GCGFB.After GCGFB was immersed in Na₂SO₄ solution,the expansion of GCGFB caused by corrosion products Aft and gypsum resulted in internal expansion cracking or even exfoliation.GCGFB lost strength and destroyed ultimately.The porosity of GCGFB in NaCl and Na₂SO₄ solution increased first and then increased with the increase of corrosion age,while that in MgCl₂ solution increased continuously.?4?The simulated overall value of the non-corroded after goaf filling was slightly increased.It can maintain the stability of the structural stress of tunnel above goaf.The paper has 67 pictures,38 tables,and 62 references.