Study On The Frost Heaving Characteristics And Antifreezing For Extra-long Highway Tunnel In High Altitude Cold Region

Sichuan and Tibet located in the intersection of the "the Belt and Road"(B&R)and the "Yangtze river economic zone." The construction of transportation infrastructure is of great significance,and the reconstruction and expansion of existing large-scale access roads have become an urgent strategic need.Among those engineering projects,the extra-long tunnels in the high-altitude cold regions are frequently encountered,and the tunneling through the frozen soil and frozen rock formations have become the major challenge of the project.In this paper,the Que'er shan extra-long highway tunnel,the highest road tunnel in the world,and other tunnels along the national road 317 were taken as the engineering background,the frost heaving characteristics and anti-freezing during the construction period and operation period were investigated by means of on-site investigation,literature review,theoretical analysis,numerical simulation,and field test.The following results are obtained:(1)The surrounding rock and composition distribution,geological and hydrological characteristics and cold climate characteristics of tunnel in typical high-altitude cold regions were investigated and analyzed.The correlations between the freezing disaster and its relevance factors such as the mileage along the tunnel,the type of surrounding rock,ventilation and ground water were investigated.The causes and the characteristics of the cold injury,the mechanism of freeze-thaw expansion and the frost heaving damage model in different tunnels were summarized.The frost heaving grading standard of moraine permafrost soil and fissured granite tunnels were discussed.Additionally,the standard is used to classify the frost heaving of the typical tunnel in high altitude cold regions.(2)The temperature field and the wind field inside and outside the tunnel during construction and operation of the tunnel are measured by the long-time,comprehensive and systematic field tests.The causes of frigid strong wind environment were revealed.Furthermore,by using the SST turbulence model,the temporal and spatial distribution pattern of temperature field and wind field in the main tunnel,horizontal guide and horizontal channel of the tunnel under different ventilation modes(especially the "horizontal guide pressure into sectional longitudinal mode" in the operation period)was clarified.(3)The accessor methods of the thermal dynamic parameters of the frozen moraine stratum in the Que'er shan tunnel were investigated,the physical characteristics and temperature characteristics of frozen soil were obtained.At the same time,based on the theory of freeze-thaw circle of frost heaving,the distribution feature of temperature field and freezing-thawing varies with time and depth in surrounding rock were obtained.The frost heave force and deformation were calculated numerically.Finally,the integrated monitoring of “temperature-hydro-mechanical” on situ for moraine stratum was proposed.The frost heaving characteristics of lining structure-moraine stratum by frost heave effect in cold area are verified through field test.(4)The defects such as cavities and discontinuity behind the tunnel linings are counted and summarized during the construction quality inspection.The hydro-thermal-stress coupling model was adopted to study the frost heave force and corresponding structural frost heave stress,damage and deformation development rule inside of the granite varied with changing of the unfrozen water volume,storage space volume and the location when the water is frozen in the granite cavity.At the same time,the influence of the internal force and deformation of the cracked water under the conditions of different crack dip angle and spacing of the fractured granite is calculated.Finally,the frost heaving characteristics of lining structure-granite rock with cavities and cracks in cold area were clarified through the in-situ observation and compared with other research results.(5)The ventilation and heating system for extra-long highway tunnel in high altitude and cold region and the anti-freezing technology for different stratum during the construction were studied respectively.The key parameters such as thermal insulation material selection,thickness and fortify range on both ends of the tunnel in the operation period are simulated and calculated.The temperature effect and the effect of thermal insulation layer were analyzed by field tests and numerical calculation.