Influence of rainfall on hydrothermal process within highway subgrade in permafrost regions
In order to clarify the impact of rainfall on the hydrothermal state within the highway subgrade in permafrost regions,a geometric similarity ratio model(1∶6)of frozen subgrade was created in a baseplate-atmosphere dual-temperature control model box,based on the environmental characteristics of the Beiluhe area of the Qinghai-Xizang Plateau and the structure of frozen subgrade.First,through a comparative experiment between no rainfall and rainfall conditions,the variation characteristics of temperature and heat flux on the pavement in permafrost regions were clarified.Then,the variation characteristics of the water field and its temperature field within the highway subgrade were further explored under both conditions,and the response of the hydrothermal state within the highway subgrade in permafrost regions to rainfall was clarified.The results show that the pavement temperature under rainfall is generally lower than that without rainfall,the heat flux at 5 cm of the pavement and shoulder shows a decreasing trend,and the heat flux of the pavement decreases more obviously,about three times the decrease in heat flux at 5 cm of the shoulder,indicating that rainfall alleviates the heat absorption within the subgrade.In addition,rainfall significantly increases the shallow water content and reduces the shallow temperature of different positions of the subgrade.Moreover,more rainfall in summer leads to more heat to be released from permafrost subgrade,and the temperature of the subgrade decreases more obviously.However,the influence of rainfall on the water content and temperature at different depths of the subgrade gradually weakens with the increase of depth,and has little influence on the water content and temperature at 50 cm and below part of different positions of the subgrade.In addition,compared with other positions of the subgrade,the increase of water content in the lower part of the natural site caused by rainfall is more obvious,while the increase of water content in the lower part of the pavement is relatively small.Although the water content in the lower part of the pavement increases less than other positions of the subgrade,the asphalt pavement absorbs more heat and leads to a higher temperature.Therefore,rainfall acting as an energy cold pulse on the pavement can lead to a more significant temperature reduction.And the temperature at 5 cm below the pavement decreases most significantly in July,with a maximum temperature drop of 2.4 ℃.1 tab,8 figs,38 refs.
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