| In recent years,China’s transportation industry has developed rapidly,and the scope of investment and construction has become larger and larger.As the construction center shifted to the western region,the number of tunnel projects in high-altitude areas has increased.The temperature difference between the four seasons and day and night in high altitude areas is obvious.Under the influence of geological conditions and repeated temperature stress,the tunnel second lining structure is likely to cause structural frost heave,cracking,water leakage and other diseases,which seriously affect the service life of the second lining structure.Therefore,tunnels in high altitude regions urgently need to solve the problems of frost heave cracking of the tunnel’s second lining structure under the effect of large temperature difference.Relying on the Guigala tunnel at high altitudes,the temperature field was measured and analyzed,and the numerical simulation was conducted to study the cracking characteristics of the second liner structure under different influencing factors and coupling effects.The performance of the second liner concrete was optimized and the following conclusions were drawn:(1)By studying the heat transfer theory of the tunnel,analyzing the heat exchange methods existing in the tunnel,and collating and analyzing the field measurement data of the Guigala tunnel,the temperature field variation law of the tunnel is obtained.The results show that the tunnel temperature field at high altitude is affected by the local There are obvious differences in climate impacts,the temperature field at the entrance of the cave is complex and diverse,and the temperature field in the cave is relatively stable;(2)In order to study the cracking characteristics of the second lining structure,an in-depth analysis of the cracking mechanism of the second lining structure of the tunnel at high altitudes,combined with the measured data,using the finite element analysis software ABAQUS to establish an analysis model under the thermal-mechanical coupling of the tunnel and calculate The three factors of large temperature difference,bias load and second liner concrete performance and the cracking characteristics of the second liner structure of the tunnel under the coupling effect are analyzed.The results show that under the effect of large temperature difference,the structure is more likely to cause damage when it is affected by other factors.Compared with the single-factor effect,the multi-factor coupling not only promotes the destruction of the structure,but also reduces the single-factor destruction under certain working conditions;(3)Through the optimization of raw materials and the optimization design of orthogonal experiments,a compound antifreeze and impermeability pumping agent suitable for high altitude areas was prepared,with the ease of concrete,mechanical strength,frost resistance and impermeability as evaluation indicators.Compared with three commonly used pumping agents,the results show that its performance is better than the commonly used pumping agents on the market.(4)Through the optimization of the mix ratio of the second liner concrete,combined with the antifreeze and impermeability pumping agent prepared in this project,the freeze resistance,impermeability,and crack resistance of the second liner concrete are tested as indicators.The results show that the optimized concrete is completely Satisfy the requirements of> F200,greatly improving the frost resistance of the second liner concrete in high altitude areas;the concrete slump meets the requirements of the specification,and has good cohesion,no bleeding,the strength is maintained at about 40 MPa,and the water seepage height H1 and H2 are 14 mm and 17 mm,respectively,and the impermeability level meets the relevant requirements of concrete in high altitude areas.Observing the appearance quality of the second lining concrete,the air bubble area and the number of cracks on the lining surface are greatly reduced after optimization. |
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