Study On Predicting The Service Life Of Highway Tunnel Lining Structures

the booming of tunneling industry in recent years, and the studying on durability of tunnel lining, durability of tunnel lining structures becomes difficulty but popular subject in tunneling research. More and more researchers and engineers have been focusing on expanding the life of tunnels. The government is working on improving normalization of expanding the life of tunnel structures. Because we are lack of the data, which determines if life of the highway tunnel structure satisfies these regulations by government in the very beginning of construction phase, the study on the theory of expansion has significant importance. Predicting the life of highway tunnel lining structures benefits us in many ways. In the operation phase, it evaluates the safety of the tunnel and roughly determines the years for security reinforcement; it revises the design concepts and standards on durability of tunnel and makes operation management more economically effective. My thesis is based on the example of Dawan sandbank tunnel. By the study on damage mechanism of tunnel lining structures and the factors to determine the life of the structures, the evaluation system is built.1. Considering the complicated conditions of the load of the structures of tunnel, special effect of atmospheric environment on it, and combined with the characters of the tunnel itself, it is clear that the damage of tunnel lining structures is mainly caused by concrete carbonization and reinforcing bar corrosion; indeed, we deeply analyze the theory of concrete carbonization and reinforcing bar corrosion. From the analysis, we come up with the model which is good for predicting concrete carbonization on highway tunnel engineering.2. Setting the final evaluation of the life to be ultimate bearing capacity, we build the evaluation of the life of tunnel lining structures system. Moreover, we split the life of the structure into two phases--the duration for reinforcing steel being non-rusty and period which damages appearing on structures.3. We define the worksite measured process parameters to predict the life of highway tunnel. The parameters include concentration of carbon dioxide, environmental temperature, relative humidity, and the working principle and operation of detecting the second lining defects. I also introduce various advanced analytical and test instruments both at home and abroad. 4. Being aimed at the structures of highway tunnel lining defects, by FLAC3D software, we have divided second lining into ten categories based on insufficient thickness and strength, and existing of loose region or cave of concrete cover. We go through numerical simulation for each category. After post data processing and calculation of safety coefficients, we get the effect of each defect with different locations and ranges on safety of the whole tunnel structure. Besides, structural defects weaken the safety coefficients of the original structure; indeed, directly shorten service life of tunnel structure.5. We use the evaluation of the life of tunnel lining structures system to evaluate the life of Dawan sandbank highway tunnel. With combining worksite measured data and data of tunnel structural defects, we conclude that the service life of Dawan sandbank tunnel does not meet the requirement, and the structural defects need to be fixed.Since my thesis states the effect of tunnel structural defects on life of tunnel lining structures, the evaluation of the life of tunnel lining structures is more practical.