降雨对多年冻土区公路路基内部水热影响试验

Influence of rainfall on hydrothermal process within highway subgrade in permafrost regions

为了明确降雨对多年冻土区公路路基内部水热状态的影响,以青藏高原北麓河地区的环境特点和多年冻土路基结构为背景,在室内底板-大气双控温模型箱内制作冻土路基的几何相似比(1∶6)模型。首先通过无降雨和有降雨工况对比试验明确2种工况下多年冻土区路面温度及热通量的变化特征,然后进一步探究2种工况下路基内部水分场及其温度场的变化特征,进而明确多年冻土区公路路基内部水热状态对降雨作用的响应情况。研究结果表明:降雨作用下路面温度普遍低于无降雨时的路面温度,且路面及路肩下部5 cm处热通量呈减小趋势,路面下部热通量减小相对更加明显,约为路肩下部热通量减小量的3倍,表明降雨作用缓解路基内部热量吸收;降雨会显著增加路基不同部位的浅层含水量,降低路基浅层温度,且夏季较多降雨量导致冻土路基释放出更多的热量,路基温度降低明显;降雨作用对路基不同部位下部含水量和温度的影响随着深度增加逐渐减弱,对路基下部50 cm及以下位置的含水量和温度基本没影响;相比路基其他部位,降雨作用导致天然场地含水量增加明显,而路面下部含水量增加较小;虽然路面下部含水量增加较小,但沥青路面吸收的热量较多导致自身温度较高,因此降雨作为能量冷脉冲作用在路面时会导致路面下部温度相比路基其他部位降低更加显著,并且7月路面下部5 cm处温度降低最为明显,最大降温达2.4℃。

In order to clarify the impact of rainfall on the hydrothermal state within the highway subgrade in permafrost regions,ageometric 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 5cm 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 5cm 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 50cm 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 5cm below the pavement decreases most significantly in July,with a maximum temperature drop of 2.4℃.1tab,8figs,38refs.