Stone Ventilation Roadbed In Permafrost Temperature Field Of Numerical Simulation And Analysis

As the permafrost is very sensitive to temperature changing, effective measures and appropriate structures must be applied to reduce the influence of embankment and preserve underlying permafrost so that the embankment can keep stability in permafrost regions, which have been the research objective for permafrost engineers and scientists.In this paper influencing factors of permafrost regime are analyzed according to climatic conditions, intrinsic factors in permafrost and characteristics of highway structure. Some advanced technologies of embankment construction in permafrost regions are also introduced. On the thermal conduction differential equation, the finite element model (FEM) of the temperature field with phase change about general embankment is founded using distinct heat capacity method. According to the heat transfer equation, the momentum equation, the energy equation about incompressible fluid in porous medium the FEM of the coupling temperature field about Air Cooled Embankment (ACE) is established by using Boussinesq approximation. The temperature fields of the general embankment and ACE in same region are calculated and compared. The operating principle of ACE is analyzed according to the velocity fields in different date. The temperature fields of ACEs are simulated in different influencing factors such as the thickness and position of rubble stratum, rubble grain size, and permafrost regions. Subsequently, the influences of different factors to ACE are analyzed in details.The analysis of simulation results shows that: ACE can preserve the underlying permafrost better and remedy the permafrost change following the construction of embankment with years. In warm season the convection is upward so that less heat is brought to embankment and in cold season the convection is downward so that more cold is brought. Therefore the periodic convection leads to a passive cooling or "thermal diode" effect. Thicker the rubble stratum is, stabler the underlying permafrost is. As the temperature difference of two embankments near thickness become lessening with the thickening of rubble stratum, the appropriate range of stratum thickness should be 0.9m~ 1.5m. Different rubble grain sizes can all preserve permafrost and the effect is better with a biger grain size. So grain sizes above 10cm are recommended. The position of rubble stratum has a remarkable influence to the temperature of ACE. As a lower position can lead to a stronger cooling effect it should be more appropriate to put the stratum straight on the surface of natural foundation. In different permafrost regions all ACEs have a cooling effect and can preserve permafrost well enough so that the upper limits of permafrost of ACEs are higher than general embankments'. Consequently, ACE is a good structure and can be used in extensive permafrost regions.