Research On Calculation Methods Of Life-Cycle Structure Performance Of Shield Tunnel In Aggressive Environments

Abstract:The designed life of shield tunnel structure in urban rail transit is100a, its occurrence condition and neighbour environements are complex and sensitive, also the train’s transporting density is high, so it is not easy to change of not once it is destroyed because of the structure decayed with the external environments action for long term, meanwhile it brings great difficult to condition acessement and prediction control of structure performance. The shield tunnel construction of urban rail transit in China, the problem of healthy service is increasingly prominent. In that, how to evaluate and predict the structure performance well and turely for ensuring well service state in its life cycle, is one of the basic scientific problems for researching urgingly.In this thesis, the calculation methods for calculating the life cycle structure performance of shield tunnel in aggresive environments were studied by means of theoretical derivation, artificial environment simulation testing and other ways, relying on the subjects supported by the National Basic Research Program of China (973:2011CB013802) and so on. And the results may provide a theory reference for the rational design and scientific maintenance of urban rail transit construction.Thesis completed the following contents:(1) The environment-time similarity theory was established based on indoor artificial environment simulation test, which has solved the correlation problem of indoor environment and field exposure test results. And then, the methods of durability design and life prediction of shield tunnel structure were put forwad, also it was extended to half probabilistic design method further.(2) The shield tunnel segment concrete durability test system coupling with erosion environment and structure load was developed. And then, the influence laws of environments ion concentration, erosion time and loading level against to the chlorine ion intrusion and distribution were discussed and proved according to the test results.(3) Based on the microstructure characteristics of concrete under uniaxial load, an analyzing model of chlorine ion intrusion were established and the calculating expressions were derived out. By using the numerical simulation method, the influence laws of environments ion concentration, corrosion time aginst to surface chloride concentration and diffusion coefficient were obtained. And then, the durability evaluation model and calculation method of sheld tunnel structure under the coupled action of erosion environments and structure loads were put forward.(4) According to the rust modes, two linear elastic plane strain models of uniform erosion and unidirectional uniform erosion were established respectively, and then, based on the thick-walled cylinder analysis theory, the calculating formulas of corroded expansion stress and displacement field were derived out, and the specific calculation method used to determine the pressure of corroded expansion were obtained.(5) The analysis model and calculation methods of rebar corrosion rate when the segment concrete cracking, were put forward by using the limit analysis theory. And then, the life-cycle evolution equation of shield tunnel structure with rebar corrosive crack damage under the uniform and unidirectional uniform corrosion, were put forward further. Finally, the normal service life prediction method and system of shield tunnel structure under rebar erosin and concrete crack were formed.(6) Proceeding from the transmission properties of segment joint, the discontinuous segment structure is transformed into a continuous non-homogeneous structure through mechanical parameters equivalent conversion at the joint local scope section, a new structure calculation model of shield tunnel named non-homogeneous equivalent beam model was established, and the analytical solutions about connector section equivalent mechanical parameters were derived. Finally, the iterative calculation process was given out.(7) A failure modes combaning by joint cross-section and the main bending moment of shield tunnel segment and the failure criterias were proposed respectively, and the calculation method of ultimate bearing capacity of shield tunnel segment structure was established based on the incremental method. Further, the bearing capacity evaluation method and safety lifetime forecasting method of shield tunnel structure coupled by the erosion environment and structure load were constructed, in which the time-varied functions of rebar corrosion rate and its mechanical properties after corroded were introduced. (8) According to the the test results and refer to the experimental data reported in existing documents, a case was calculated and analyzed as an example. The results indicate that the calculation methods of life cycle strcuctre performance of shield tunnel, advanced in this thesis, under coupling action of aggressive environments and structure loads is reliable, and has well maneuverability; the non-homogeneous equivalent beam model can better reflect the impact of the existence of joint aginst to the overall stiffness of segment structure, its calculation results are reliable, and has good convergence.