多年冻土区高等级公路特殊路基长期降温效果研究

Study of the long-term cooling effect of special embankments of high-grade highways in permafrost regions

气候变暖背景下,块石路基及通风管-封闭块石基底复合路基成为多年冻土区高等级公路冷却路基的主要结构形式.为探明不同直径块石层的渗流特征和规律,开展了立方排列球体室内风洞试验,一方面获得了渗透率和惯性阻力系数及其与球体直径间的统计关系;另一方面得到了球体层内部压力梯度与渗流速度呈二次非线性关系.基于该试验得到的参数和关系,采用多孔介质中流固耦合传热模型,通过有限体积法模拟了柴木铁路块石路基的降温效果,并利用实测数据验证了模型及参数的可靠性.在此基础之上,以青藏高等级公路特殊路基为原型,使用该传热模型开展了封闭块石基底路基和通风管-块石复合路基长期冷却降温效果的数值模拟研究.结果表明:封闭块石基底路基和通风管-封闭块石复合路基在研究期内均有降温效果,可以提高路基下人为上限,而块石夹层路基在一定时期内可以提高冻土上限,但下部土体温度升高,长期降温效果较差.

Considering the climate warming, the block stone embankment and the ventilation duct-closed block stone embankment are becoming the major structures of cooling embankments in permafrost regions. In order to obtain the seepage characteristics and the properties of block stone layers with different sizes, wind tunnel tests were carried out in this study. On the one hand, the statistical relationships between the permeability/inertial re- sistance coefficient and the cement bali＇s diameter were gotten. On the other hand, the nonlinear quadratic curve relationship between the internal air pressure gradient and the seepage velocity within the cement ball layer were acquired. In addition, based on the parameters and relationships from the wind tunnel test, coupled heat transfer model in porous media was used to analyze the cooling effect of the close block stone embankment in the Chai- Mu Railway using finite volume method, and the reliability of the numerical model and parameters were verified by the observed values. Furthermore, the long cooling effects of the closed block stone embankment, the block stone interlayer embankment and the ventilation duct-closed block stone embankment in the Qinghai-Tibet High- Grade Road were analyzed through the closed block stone embankment model. It is found that the closed block stone embankment and the ventilation duct-closed block stone embankment could cool down the permafrost effec- tively, raise the artificial permafrost table and insure the artificial permafrost table higher than the original one in the background of climate warming in the study period. The block stone interlayer embankment could raise the artificial permafrost table in a short period of time, but the temperature of permafrost under the embankment would be elevated.