Study On The Design Philosophy Of Prestressed Concrete Linings For Shield Tunnel

Shield tunnel has been widely used in the construction of subway, underwatertunnels and underground pipeline projects, etc. Because of the connaturalcharacteristics of the concrete, the normal reinforced concrete segments have manydisadvantages, such as heavy weight, difficulty of crack control and lower ofbearing tensile force, etc. To the bolt connection of segments, the cost is expensive,and the construction procedure is complex. Overcoming the disadvantages ofcommon concrete as well as being used as an assembling method, the prestressedconcrete is widely used in engineering structures. In order to introduce theprestressing method into the structure of shield tunnel lining, it is necessary to studythe desigri philosophy of prestressed concrete linings. The study can not only guidethe design and constructions of shield tunnel prestressed segments scientifically, butalso promote the applications of prestressed segment.Based on the literatures and the existent researches, the study on segments jointof prestressed lining has been carried out. Firstly, the theoretical equations forcalculating the opening angle of the joint are deduced. Compared With the results ofexperiments and numerical simulations, the calculated value suggests that thetheoretical equations are reliable. Secondly, the influences of different prestressingcable positions and varying eccentricities on the joint characteristics have beendiscussed. Finally, the ratio of prestressing to axial force is defined. And itsinfluence to the joint characteristics has been also discussed.With the load-structure method, the structure model of prestressed lining hasbeen studied. The effects of prestressing on the tunnel lining include the effects onthe segment joint and the effects on the lining ring. The equivalent load ofprestressing can be used to represent the effects on the lining ring. Compared withthe beam-spring model and the modified-routine-method model, thecontinuous-nonuniform-rigidity model—a new structure model of tunnel lining hasbeen brought up in this thesis. The new model can not only represent the effects ofprestressing on the segment joint, but also show the moment redistribution aroused by the rigidity's decrease of the joint. Combined with the case study, the calculationprocess for the prestressed lining structure is given. And the results of theoreticalcalculations and numerical simulations are compared. At the same time, the newmodel is used to analyze the effect of ratio of prestressing to axial force on thelining structure.According to the probability-based limit state design method and the concept ofprestressing degree, the design method of prestressed lining has been discussed. Thedesign process is given. The detail for calculation and constructional design are alsoanalyzed.Using the design philosophy of prestressed concrete linings discussed above, asubway tunnel lining and a water transport tunnel lining have been designed. Basedon these tunnel designs, the technical economy analysis of prestressed concretelinings has been mentioned.