Study On The Equivalent Mechanical Model And Application Of Composite Segment In Shield Tunnel

Shield technology is the best choice to build the following large infrastructures in cities because this method is environmental,safe and high efficient.These infrastructures include rail transit,underground pedestrian passageway and underground reservoir.Composite segment is gradually exploited in shield tunnels because of outstanding mechanical features.However,composite segment has many constituent materials,and the differences in these materials make the analysis method and calculation model of concerned segment hard to be unified,which add difficulties in design.Meanwhile,the influencing factors affect one another in the segment.It is quite difficult for designers to set and control those parameters during model calculation without the he lp of experimental data.Consequently,these difficulties in design are the most critical reasons that restrict the wide application of composite segment.O n the other hand,the structural form of composite segment is various and complicated.This makes the manufacturing procedure complex and enlarges the period and cost of manufacture.Under the coupling of surrounding strata and structural form,the calculations of segmental ring,which comprised of several composite segments,are out of convergence.Therefore,it can simplify the structural model when composite segment is equivalent to single and homogenous structure,and can bring convenience to designers and researchers.Also,equivalent segments can increase the precision of segmental rings and thus reduce the calculation difficulties and workloads.Based on the theories of elastic-plastic mechanics and existing experimental results,therefore,a series of precise numerical models were firstly established for composite segment using ABAQUS in this paper.And the mechanical behaviors under bending moment and combined forces were researched respectively.The sensitivities of steel tubes were analyzed with the carrying capacity of segment.The strain distributions of steel tubes were investigated to study their influences and consequently,a simplified method was developed to determine the influence range of main girder and skin plate.Meanwhile,equivalent models were built according to energy equivalent principle.Making use of the equivalent results,this paper proposed two equivalent methods,width equivalence and height equivalence.The fitting equations between steel tubes' s thickness and equivalent dimensions were obtained for main girder and skin plate respectively.Finally,the characteristics of two equivalences were discussed and their combination results were presented in three-dimensional coordinate.Results in this paper show that the influence ranges and equivalent dimensions of steel tubes' thicknesses have the identical changing laws with the increment of their thickness.The two equivalent methods and their combinations can provide theoretical references for the equivalent calculations of composite segment and reduce its design difficulties.