Study On Tunnel Limit Displacement In Different Construction Stages Under The Condition Of Surrounding Rock Damage

The existing limit displacement and its management reference are mainly obtained under the closure of supporting structure to the universal railway tunnel section,without considering the damage of surrounding rock and the tunnel construction stages.However,existing tunnel instability case study results show that the tunnel instability can occur in any tunnel construction stage,and tend to occur before the supporting structure closed.Therefore,it is of great significance to study the tunnel limit displacement in different construction stages,which is based on surrounding rock damage.Based on the theory of damage and unloading of surrounding rock,the IV₂ and V-level surrounding rock high speed railway tunnel vault displacement of different construction stages is simulated by FLAC3D software with considering different buried depth,the tunnel vault limit displacement is determined by the point mutation theory.At the same time,the sensitivity of the surrounding rock parameters to the tunnel vault limit displacement is analyzed with grey correlation,and the following conclusions are drawn:（1）The same buried depth and the same surrounding rock grade tunnel have the same time of plastic zone appearing around the hole in different construction stage.Different buried depth and the same surrounding rock grade tunnel,the time of plastic zone appearing in the same construction stage is different.The greater buried depth is,the smaller stress release rate corresponding to the plastic zone is.（2）Under the condition of calculating buried depth from 50 m to 300 m,both IV₂-level surrounding rock tunnel and V-level surrounding rock tunnel have a linear relationship between the limit displacement and burial depth in the same construction stage.（3）Whether IV₂-level surrounding rock tunnel or V-level surrounding rock tunnel,the limit vault displacement of the upper step contributing to final vault limit displacement is dominant,the contribution can reach 90%at IV₂-level surrounding rock tunnel and 70%at V-level surrounding rock tunnel.（4）In the same construction stage,the limit stress release rate not considering surrounding rock damage is larger than that considering damage.Thus the vault limit displacement neglecting considering surrounding rock damage is larger than that considering damage.（5）Whether IV₂-level surrounding rock tunnel or V-level surrounding rock tunnel,the surrounding rock parameters sensibility is consistent to the vault limit displacement in different construction stages.The results show that the degree of impact on the vault limit displacement is ordered from largest to smallest:p,c,v,φand E.