Numerical Simulation Of Freeze Temperature Field And Frost Heave In Subway Tunnel Construction With Artificial Ground Freezing Method

With the development of social economy and increasing of urban population, the building ceaselessly develops to higher and underground space. Exploiting underground space has become an important means to expand living space, and constructing subway will be oneof the most powerful means to exploit underground space .Due to the artificial freezing method can adapt to a variety of complex engineering geological and hydro-geological conditions, and can make up for defects of tunnel shield. Non smoking, clean, less pollution, and suitable for construction in the city, and does not affect the normal operation of the urban economy, etc, so this method is made use of subway construction in wide. However, people can not accurately know the development of frozen wall, the temperature field and the surface displacement caused by frost heave. So accidents occur in construction of the freezing method such as road cracks, subsidence, structural crack, based on the pull etc.To these questions, the large-scale numerical computation software ANSYS was adopted. By setting different enthalpy to soil under different temperatures for consideration numerical simulation model of the water phase-change phenomenon. Through a large number of numerical experiments to quantify the study of a variety of soil under the salt water temperature, pipe diameter, freezing tube spacing, soil water parameters such as temperature of frozen wall on the influence of temperature. Through adopting negative thermal expansion coefficient of the method to consider artificial freezing in the process of surface frost heave problem. Using a variety of programs of numerical experiments, focus on depth of the tunnel, freezing wall thickness, radius of the tunnel excavation, the rate of soil parameters such as frost heave on the subway level of the freezing of the surface frost heave displacement method to quantify the orderliness of influence. The following is quantitative conclusions:Firstly, the thickness of frozen wall along with the time of freeze to growth of the linear; at the same time of freeze pipe wall thickness with increasing diameter; decreases of freeze pipe spacing, lower brine temperature; reduce water content and increasing; with the time of freeze growth of various factors at different levels of the freeze wall thickness increasing the margin.Secondly, freeze tube diameter not less than the best 10cm in the construction;freeze pipe spacing of not more than 0.8m;for clay, salt water temperature no higher than -22℃;silty clay and sub-sandy soil; salt water temperature no higher than -26℃.Thirdly, the freezing rate growth along with the freezing time; reduce at first then gently; at last the trend has increased.Fourthly, changes in various factors impact of frozen wall descending order: Brine temperature, freezing tube spacing, tube diameter freeze.Fifthly, surface vertical and horizontal displacement decrease with the increase of tunnel depth.Sixthly, surface vertical and horizontal displacement increase with increasing of the artificial freezing thickness.Seventhly, surface vertical and horizontal displacement increase with increasing of radius of subway tunnel excavation.Eighthly, surface vertical and horizontal displacement increased with the rate of frost heave of fast growing.