Evaluation Of Existing Shield Tunnel

With increasing age of service, the structures of many existing urban shield tunnel have faced the damage and degradation in our country. During the period of transition from construction to maintenance of the shield tunnel, it has became research hot issue currently about how to ensure the safety and durability of the exiting tunnel, how to improve the applicability and maintainability of the existing tunnel and how to prolong the service life of the existing tunnel. So the evaluation of existing shield tunnel appears more important.The dissertation is supported by National Natural Science Foundation of China 'the durability and service life of the concrete lining of the underground structures' (Grant No.50678135), 863 Program of China 'the construction technology of the urban underground space'(Grant No.2006AA11Z118) and National Key Technology R&D Program 'the core construction technology of the large river crossing shield tunnel' (Grant No.2006BAJ27B02-02). The index for the existing tunnel evaluation is presented and the tasks of the implementation of tunnel inspection are grouped and aim is to provide data for safety and serviceability evaluation of tunnel structure. Based on the lateral analytical model, the identified method for the damage parameters of existing tunnel structure is put forward by applying optimization back analysis methods. And the longitudinal deformation of the first crossing river tunnel in our country was analyzed. Finally the durable deterioration model was presented. The model included capillary suction, permeation action, diffusion action and evaporation action in concrete lining and the electrochemical corrosion to the lining bolts. By applying Bayesian conditional probability and the inspection data the durable model can be updating. Some main works and results about the dissertation were listed as follow.1,The dissertation discuss the composition and working flow of the evaluation system for existing tunnel. The structure's safety and durability make of the serviceability of the existing tunnel. The indexes of the evaluation include three parts, one major part is the integrity performance, other part is safety index and another part is durable index.2,the outlines the implementation of tunnel inspection were made up in this dissertation by combining preliminary investigation, some code and standard, and structural analysis. The inspections include routine inspection and additional inspection. All the items of the routine inspection must be inspected in one inspection period. According to the results of the structural re-analysis, the additional inspection items can be selected.3,The damage identified method was presented for the damage parameters of existing tunnel structure. Applying optimization back analysis methods and the tunnel analytical model combining bending stiffness, longitudinal joints and elastic soil, this method can identify elastic modulus of the lining concrete and the rotational stiffness of the longitudinal joints.4,The longitudinal model of shield tunnel was discussed. The reaction of the adjacent lining ring and the resistance of the elastic soil were considered in this model. And the long-term longitudinal structural deformation of the first crossing river tunnel in our country was analyzed.5,The durable deterioration model of tunnel lining was presented. The model discussed the harmful substance ingresses into concrete lining by the capillary suction, permeation action, diffusion action and evaporation action, and the electrochemical corrosion to the lining bolts. By applying Bayesian conditional probability and the inspection data the durable model can be updating.6,The dissertation analyzed the limit state equations in initiation period and propagation period. In initiation period, for the concrete carbonation the limit state can be defined when carbonation depth reached concrete cover, for the chloride ingress the limit state of can be defined when chloride concentration reached critical value, for bolt corrosion the limit state can be defined when section losing of bolt reach critical value. The propagation period describe the procedure form cracking to penetration depth of the reinforcement leading to collapse.7,Markov Process and Reliability Theory were introduced for evaluating the condition state of the existing tunnel structure. At the same time the condition states of the service life and transition probability matrix of the deterioration processes and MR&R actions were given for the Markov Process.