| It is well-known that construction of high-speed long rail tunnel in the Qinghai Tibet Plateau will encounter a series of risks and unsolvable complex geological difficulties since its high-speed rail tunnel’s construction standards are higher. Lanxin railway is the high-speed railway with highest altitude in the world, Daliangshan tunnel and Qilianshan tunnel are located at the highest elevation points of Lanxin railway,3800 meters, also the high-speed rail tunnel with highest elevation point in the world currently. During its process of construction, many unexpected difficulties are encountered that need to carry out scientific and technological innovation research.Based on the construction of these two tunnels mentioned above, experiments and research were carryed out. The main works are:construction technology of tunnel through debris flow strata, construction control technology of large deformation of tunnel in thin slate rock with high ground-stress, research of quantitative index about reduction of mechanical efficiency in large and long tunnel in the plateau. The results of research are listed as follows:(1) The engineering properties of debris flow are revealed through theoretical analysis and field test. It is mainly composed of fault breccias, clastic particles, sand and water mixture material with big density, high viscosity, strong liquidity, bust characteristics, and the distribution range is wide and it is difficult to predict in tunnel construction. Through the research on the formation mechanism of debris flow in tunnel construction, three stages of the formation of debris flow are presented:precursor stage, influencing stage, developing stage.(2) Combined with the engineering construction of debris flow section of Qilian Mountain Tunnel, using the field test and theoretical analysis method, this paper studies the tunnel supporting technology and excavation method, and the core construction technology of tunnel with large section in debris flow layer is put forward:ahead forecast of clastic body, tunnel face plugging, high drainage in advance, strong support in advance, primary strong support.(3) Combined with large deformation control problem of Daliangshan tunnel in thin slate rock with high ground-stress, through the field test of the geostress and the test analysis of characteristics of surrounding rock, it is concluded that the horizontal ground stress (7.18 to 25.14MPa) is greater than vertical geostress, the ratio of rock stress is in the range of 0.025～0.126 that reveals the thin slate section’s deformation is compressive large deformation in Daliangshan tunnel, the large deformation of tunnel in thin slate with high ground-stress can be divided into 4 levels:severe large deformation, secondary large deformation, slightly large deformation and no large deformation.(4) Field tests and numerical analysis indicate that the ground condition has little improvement due to the poor performance of Vc-2 systematic rock bolts. The comparison tests of single-layer steel gird support, single-layer steel arch support of H175 and the combination of steel gird and double-layer steel arch of 120 support show that the double-layer support system has a better control of the deformation of the surrounding rocks, the single-layer gird performs poorly.(5) Four test sections of different increase of the support parameter and preset deformation are selected in the severe deformation zone. A proposed preset deformation of 50cm is given. It turns out that this value possesses a more than 90% probability of un-invasion according to a large amount of data statistics of tunnel deformation. (6) Based on the plateau environment lab with nitrogen gas mixing of the engine intake method, a simulation system for the performance test of diesel engine in long tunnel environment is designed. The quantitative evaluation method for the efficiency decrease of construction machinery under the environment of long tunnel in plateau is formed. |
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