Study On Influencing Factors And Influence Law Of Lateral Mechanical Characteristic Of Double Lining Of Shield Tunnel

With the extensive application of shield technology in underground traffic,it meets more and more challenges in fracture surface,and its occurrence environment become much more complex.The existing single segment lining of shield tunnel is hard to meet the requirements of bearing capacity,durability and waterproof.In order to meet the requirements above,some domestic cities have begun to do secondary lining in shield tunnel.But there is still a lack of effects of occurrence conditions,structure form and structure defects on mechanical properties of double lining structure of shield tunnel.Combing highway,railway and subway tunnel engineering prototype,using theoretical analysis and model experiments,this paper carries out systematic researches on the bearing mechanical properties of double lining structure of shield tunnel influencing by different side pressure coefficient,water pressure,shield tunnel scale,secondary liner thickness,reinforced secondary liner,the depth and spatial distribution of secondary liner effects.Here are research results obtained:(1)With the increase of side pressure coefficient,the double lining's ultimate bearing capacity increases.But the destroy process gradually becomes into paroxysmal from gradualness.When the side pressure coefficient is under 0.5,making secondary lining becomes more efficient in increasing the double lining's ultimate bearing capacity.(2)In a certain range,the increased pressure can improve the duct piece and double lining's ultimate bearing capacity.But the destroy process tend to be paroxysmal.In circulating water pressure,the greater the variation of water pressure,the lower the ultimate bearing capacity of the duct piece.And it is more advantageous to make secondary lining as early as possible for the overall bearing capacity of the structure.(3)Basing on the present shield tunnel's selection of design parameters,with the increase of shield tunnel scale,the duct piece and secondary lining structure's side rigidity becomes relatively smaller,and duct piece and double lining's ultimate bearing capacity decreases.When the outer diameter of shield tunnel exceeds 10m,make secondary lining becomes more effective in improving stress and increasing the ultimate bearing capacity of duct piece and secondary lining.(4)With the certain thickness of duct piece,increasing the thickness of secondary lining can improve the ultimate bearing capacity of duct piece and secondary lining evidently.The destroy process tend to be paroxysmal.When the secondary lining's thickness exceeds 30cm,increasing the thickness of secondary lining gradually becomes less effective in improving the ultimate bearing capacity of secondary lining.(5)The secondary lining reinforcement can increase the ductility of double lining,effectively improve the ultimate bearing capacity of double layer lining,prolong the process of destabilizing destroy and improve the overall bearing capacity of the double lining.(6)Secondary lining defects has obvious effects the on the stress state and the ultimate bearing capacity of double layer lining.The larger the defect scale,the lower the double layer lining's ultimate bearing capacity.The · overall destabilizing destroy tend to be paroxysmal.And secondary lining defects on vault and haunch have more obvious effects in decreasing the double layer lining's ultimate bearing capacity.