| Combining with the international frontier issues on freeze-thaw damage, cold-proof and thermal insulation in the construction of tunnel engineering in cold region with high altitude, Galongla tunnel which is an important part of Za-mo highway in Tibet is studied in this paper. The mechanism of frost heave for rock tunnel and related insulation technology are studied. The thermo-hydro-mechanical-damage (THMD) coupled model of rock tunnel in cold region under the ventilation condition is established. Researches on the related theoretic model and application technology are done with laboratory test, theoretic analysis, numerical simulation and field measurements. A method is proposed to do the stability analysis of tunnel in cold region with high altitude under frost heaving force and the related reasonable cold-proof measure is presented. There are two significances. Firstly, the THMD coupled model of tunnel in cold region under the ventilation condition is established, which is a theoretic extension of mechanism of frost heave for rock tunnel in cold region. Secondly, a pioneering work is done on the optimum design for tunnel support structure in cold region and the establishment for reasonable cold-proof measures. The conclusions of this study are list as follows.(1) The controlling equations for thermo-hydro coupled model of low-temperature rock mass considering phase change are established and a new method is proposed for calculation of thermal conductivity coefficient of geotechnical material considering the phase change under low temperature.According to the basic law of water flow and heat transfer in rock mass under freezing-thawing condition, the controlling equations for thermo-hydro (TH) coupled model of low-temperature rock mass considering phase change are established based on the theories of continuum mechanics, thermodynamics and segregation potential. These equations include not only the effect of heat conductivity, latent heat of phase change and the seepage velocity on temperature distribution but also the effect of water flow in pore resulted by Soret effect and segregation potential on seepage velocity and seepage pressure distribution. And the total bi-directional coupling between seepage field and temperature field is realized. Compared with the famous TH coupling laboratory test conducted by Mizoguchi et. al., the presented TH coupled model is verified and the reasonability of determination of related material parameters are proved. Meanwhile, the systematic summarizations are done to the related thermodynamic parameters for the TH coupled model. For geotechnical material, there are many pores and the unfrozen water still exists when the temperature is below 0℃. Combining with the above characteristic and aiming at the shortage of the three current methods for calculating the heat conductivity coefficient of geotechnical material, a new method is proposed to calculate the heat conductivity coefficient of geotechnical material with low-temperature considering phase change based on random mixed model (RMM). Through the comparison with Mizoguchi's experiment results, the new method is verified.This model is an extension of the current HM coupled of low-temperature rock mass considering phase change, and provides a new method to determine the heat conductivity coefficient of rock mass.(2) Considering the effects of air temperature and humidity, the turbulence model of air-flow field in tunnel is established and the heat exchange law between surrounding rock and air-flow field in tunnel is studied.Based on the theories and methods of hydrodynamics, heat-transfer and aerodynamics, some researches on ventilation in subway and building energy efficiency are lead in to establish the turbulence model of air-flow field considering the effects of air temperature and humidity. Based analysis of current research on turbulence numerical simulation method and heat exchange law between air and surrounding rock, the proposed turbulence model is adopted and a numerical simulation for Baly's laboratory experiment on mixed convection with reduced scale model is done. Comparing with the experiment results and numerical results from Ma et.al., the proposed turbulence model is verified and its advantages are presented. Based on the above studies, the numerical analysis is done to study the effects of air temperature, air humidity and air speed on temperature distribution of surrounding rock in tunnel. It is concluded that:air temperature and air speed are two important factors which significantly affect the temperature distribution of surrounding rock in tunnel. In contrast, the effect of air humidity on temperature field is much smaller.The turbulence model is an extension research on temperature field of surrounding rock in tunnel in cold region and can be applied to the related ventilation numerical simulation such as ventilation of subway, fire modeling, building energy efficiency, indoor environment and so on.(3) A damage factor is proposed to consider the freezing-thawing effect in rock and the damage constitutive model considering the freezing-thawing is presented to describe the stress-strain relationship of surrounding rock for Galongla tunnel in Tibet.The freezing-thawing laboratory test, uniaxial compression test and triaxial compression test are done with the samples from Galongla tunnel in Tibet. The failure forms, strength, deformation and degradation characteristics of rock under different freezing-thawing condition are analyzed. It is concluded that:the main failure form of rock under uniaxial compression is splitting failure and that under triaxial compression is shear failure. The strength decreases with the increasing of numbers of freezing-thawing. The axial strain corresponding to the peak stress increases with the increasing of confining pressure and numbers of freezing-thawing. Based on the above researches, a damage factor is proposed to consider the freezing-thawing effect in rock and the damage constitutive model considering the freezing-thawing is presented to describe the stress-strain relationship of surrounding rock for Galongla tunnel in Tibet.With this model, the damage characteristic of rock in the process of freezing-thawing is described and a foundation is provided to reveal the mechanism of freezing-thawing damage for engineering rock mass.(4) The THMD coupled model for tunnel in cold region under ventilation is established.The THMD coupled model for tunnel in cold region under ventilation is established, considering the effect of volume strain on temperature and seepage field of surrounding rock and the effect of temperature gradient, seepage pressure and frost heave pressure on mechanical field. Besides three traditional controlling equations for THM coupling (energy conservation equation, mass conservation equation and balance equation), there are turbulence equations considering the effects of air temperature, air humidity and air speed in tunnel in the proposed model. Based on the above study, a numerical simulation is done to model the frost heave process of a pipeline engineering in cold region. Compared with the field measurements, it is concluded that:the frost heave phenomenon caused by temperature variation in surrounding rock can be described well and truly with the proposed model.Based on the THM coupled theory, the proposed model is a new exploration on mechanism of frost heave of rock in tunnel in cold region under complex ventilation condition. And this model is much closer to the actual situation for tunnel engineering in cold region.(5) A high-performance foamed concrete is designed. Its insulation properties and degradation characteristics under freezing-thawing are studied through laboratory test and the numerical analysis is done to study the insulation effect in tunnel in cold region.Aiming at the characteristics of tunnel in cold region and based on the investigation of foamed concrete products,9 types of material are chosen to be the basic materials of the designed foamed concrete such as obturator perlite, polypropylene fibers and so on. With the orthogonal test, the effect of each basic material on performance of foamed concrete is studied. The results show that the contents of foam, obturator perlite and polypropylene fibers are the main factors which affect each characteristics of foamed concrete. According to the orthogonal test results, the optimal formula is established to make up a high-performance foamed concrete. Its insulation property and degradation characteristics under freezing-thawing are studied particularly. The experimental results show that this foamed concrete is suitable for application to the insulation layer and anti-seismic layer in engineering in cold region which has the characteristics of lightweight, cold-proof, crack resistance and anti-seismic. Based on the above research, the insulation effect in tunnel in cold region is studied by numerical simulation.With this foamed concrete, the design of insulation and anti-seismic of tunnel in cold region are integrated together.(6) Combining with the Galongla tunnel engineering in Tibet, many field tests are done and a remote wireless monitor and health diagnose system in tunnel is presented.There are many characteristics in Galongla tunnel which locates at the Himalaya fault zone in Tibet, such as high altitude, low temperature, large rainfall and different climate at the entrance and exit of tunnel. Aiming at those characteristics, many monitoring equipments are installed in situ such as temperature sensor, osmometer, pressure cell, steel bar meter, concrete strain gauge and Seismic accelerometer. With GPRS technology, a remote wireless health diagnose system is designed to monitor the temperature distribution, underground water seepage and stress status of structure and surrounding rock in tunnel.With this monitor system, the measurements can be done under any severe environment condition and cost less resources compared with those traditional monitor methods. The basis is provided for construction and maintenance of Galongla tunnel and many precious technical data are provided for tunnel in cold region. A new method is proposed for stability prediction and long-term monitor of tunnel engineering in cold region.(7) Aiming at Galongla tunnel, the material type, depth, location and length for cold-proof and insulation are determined and the frost heave force of surrounding rock in an extreme climate is obtained. The stability analysis of tunnel under long-term freezing-thawing cycle is done.With the above theoretic and experimental results, the length of insulation material near the entrance and exit of tunnel and the frost heave force in an extreme climate in Galongla tunnel are studied. The stability analysis of tunnel under long-term freezing-thawing cycle is done. It is concluded that:1) 600m far from the entrance of tunnel and 400 m far from the exit of tunnel, the application of insulation material with a depth of 6cm at the surface of secondary lining can prevent the lining and surrounding rock from freezing-thawing damage effectively for Galongla tunnel.2) the frost heave force of surrounding rock of tunnel in an extreme climate reaches to 1.6MPa.With this part of work, the above theoretic and experimental results are applied to an actual projects and are verified.
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