Study On Characteristics Of Water-thermal Field And Stability Of Highway Subgrade In Seasonal Permafrost

Frozen soil is widely distributed in China,and roads and railways constructed in frozen soil areas generally suffer from frost damage.In order to ensure the durability,comfort and driving safety of subgrade and pavement,problems such as frost heave and thaw settlement need to be solved urgently.With the change of seasons,the deformation and stability failure of seasonally frozen soil roadbed is the result of the combined action of temperature field,moisture field,and stress field.Among them,the essence of soil frost heave and thaw settlement deformation stability is a multi-physics coupling problem.Its coupling mechanism involving heat and mass transfer,fluid mechanics,elastic-plastic mechanics,and many other disciplines,is extremely complex,therefore strengthen the embankment temperature field,moisture field and deformation field and the change of the stability of the roadbed,to improve the seasonal frozen soil subgrade design,construction and maintenance and so on all has the guiding significance of cannot be ignored.The paper takes the expressway subgrade of Shuangliao to Nenjiang connection lineShuangliao to Taonan section as the research object,and uses the finite element software COMSOL Multiphysics secondary development module to realize the calculation of the simplified mathematical model with relative saturation,solid-liquid ratio and so on.In this way,the full coupling numerical simulation of temperature field and moisture field is realized,and the classical freezing test of soil column under constant temperature is inversion,and the simulation results are in good agreement with the test results.Then,the temperature field,moisture field and deformation field of the subgrade in the seasonal frozen soil area are numerically simulated and analyzed,and the frost heaving and thawing settlement amount and the maximum frost depth of the subgrade with the seasonal change are calculated,which provides a certain basis for analyzing the internal laws of the subgrade in the seasonal frozen soil.Finally,based on the finite element strength reduction method,the variation of safety factor of subgrade slope with thawing depth,water content,number of freeze-thaw cycles,freezing temperature and slope of seasonal frozen soil subgrade is analyzed,and the influence law on the stability of subgrade slope is analyzed.The results show that in the process of freezing and thawing,water will migrate from the frozen zone to the unfrozen zone,and the stability of water field will lag behind the temperature field.The change of air temperature has great influence on the change of water content of shallow soil inside the seasonal frozen soil subgrade,but little influence on the change of deep soil water content inside the subgrade.After years of freeze-thaw cycles,if the subgrade evaporation and drainage are not taken into account,the water will continue to accumulate on the surface of the subgrade and foundation,which will eventually lead to the increasing amount of frost heaving and thawing settlement of the subgrade when the weather gets cold and warm.It is easy to cause the uneven deformation of the road surface,resulting in the destruction of the roadbed.The analysis of strength reduction method shows that the safety factor of subgrade slope decreases with the increase of subgrade thawing depth.In addition,it is found that when the thawing depth is constant,with the decrease of freezing temperature,the increase of slope slope and the increase of the number of freeze-thaw cycles,the slope safety factor will decrease continuously,and the slope stability will decrease.However,when the water content changes in the range of 8%-10%,the slope safety factor increases.When the water content,slope and freezing temperature are constant,the safety factor of the slope decreases and the stability of the slope decreases with the increase of thawing depth.