Study On The Vibration Response And Fatigue Life Of High-speed Railway Tunnels Based On Damage Theory

More and more high-speed railway tunnels are being built in our country, while the research on dynamic responses of high-speed railway tunnels is relatively lagging behind, especially the study on dynamic damage and fatigue properties of high-speed railway tunnels. In response to this shortage of research, this dissertation, supported by the National natural Science Foundation Project of China (NO.550778178), studies dynamic responses and damage characteristics of current double-track high-speed railway tunnels systematically by using methods such as theoretical analysis, numerical calculation and model test. The damage of linings is quantified and the analysis on fatigue life of high-speed railway tunnels, together with their damage mechanisms, is carried on. The main research contents and conclusions are as follows:(1) Based on the exiting damage models, the damage equations considering initial damage of concrete under uniaxial tensile stress state and uniacial compressive stress state are established respectively. Then a double-scalar damage variable combined with a tensile damage variable and a compressive damage variable is presented to describe the damage properties of concrete. By introducing the defined double-scalar damage variable into Drucker-Prager yield criterion, an elastoplastic damage constitutive model is proposed with a non-associated flow rule.(2) Specific numerical algorithm and calculation flow processes including elastic guesses, plastic corrections, damage modification and stress correction are designed for the proposed model. Corresponding calculation program is compiled as well. By means of the interface of finite difference software FLAC5.0, redevelopment is carried out to program the damage model. Through comparing the results of previous tests with their numerical results by applying the redeveloped damage model, effectiveness of the proposed model is verified.(3) Taking the current double-track high-speed railway tunnels (general type) inâ…£orâ…¤class surrounding rocks as research objects, dynamic responses and damage characteristics of linings are studied systemically with the redeveloped damage model. The results show that:the development process of dynamic damage coincides with the time history of dynamic responses; responses and damage of linings are significantly influenced by surrounding rock conditions and increase as train speed increases; dynamic damage of linings is closely related to the initial damage. The more initial damage, the more dynamic damage that caused by train vibration. (4) According to Similarity Theory, dynamic model tests under different loading frequencies, namely train speed, are designed and performed for bottom structures of high-speed railway tunnels. Not only are the stress characteristics, dynamic coefficient, dynamic strain of inverts and accumulative vertical displacement of rails emphatically analyzed, their relation with loading frequency and loading cycles are also discussed in details. The test results show that:the bottom of inverts is mainly in a tensile stress state and the circumferential stress is higher than the longitudinal stress; the circumferential dynamic coefficient is also larger than the longitudinal one; the stress, dynamic coefficient of inverts and accumulative displacement of rails increase as loading frequency and loading cycles increase. Furthermore, dynamic strain and accumulative displacement are logarithmically related to loading cycles.(5) On the basis of numerical and model test results, tensile fatigue equations from S-N curves of concrete and Miner linear damage cumulative theory are adopted to predict the life of high-speed railway tunnels. The calculation results indicate that under the given calculation conditions along with the estimated vehicle flow in this dissertation, the anti-fatigue performance of tunnel structures designed for IV class surrounding rocks is enough to meet the stability requirement during design reference period(100 years). But that forâ…£class surrounding rocks is not enough to meet requirement, if trains run through tunnels at a speed of 300km/h.(6) In terms of damage cumulative theory, the fatigue damage mechanisms of high-speed railway tunnel structures is explained in details. The main factors (those have great influence on the fatigue life of tunnels) are listed. Then, some effective measures to improve the serve life of high-speed railway tunnel structures are emphasized.