高海拔多年冻土区高速公路分离式通风管路基的降温效果研究

Study on the cooling effect of separated duct-ventilated embankments used for the Qinghai—Tibet expressway in high-altitude permafrost zones

考虑到宽幅路基的“聚热效应”和复杂的多年冻土环境,拟建青藏高速公路建设所面临的关键问题是如何保证路基的长期热稳定性。基于现场监测数据和传热传质理论,建立分离式通风管路基三维数值模型,分析与预测未来50年通风管在青藏高速公路分离式路基中的工程效果。结果表明:分离式通风管路基具有较好的降温效果,能够保证路基及其下部多年冻土的长期热稳定性。但是,当隔离带宽度小于10m时,后幅路基管道内部风流变化特征受到隔离带宽度的显著影响,导致其对下部多年冻土的降温效果弱于前幅路基。此外,在隔离带较窄情况下,两幅路基之间隔离带区域存在局地增温效应,将对路基及其下部多年冻土产生严重的热扰动,不仅引起多年冻土上限下降、温度升高,而且增加了路基两侧下部土体温度场的不对称性。尝试将两幅路基通风管连通来弱化局地增温效应,但连通后路基及隔离带区域下部土体的热状况反而更差,说明这种方法未能有效解决局地增温效应的热影响。

Considering the significant heat absorption of wide embankment and the complex permafrost environment,ensuring the long-term thermal stability of embankment is the key problem of the construction of proposed Qinghai—Tibet expressway.Based on the field measured data and the heat and mass transfer theory,this paper developed a three-dimensional numerical model of the separated duct-ventilated embankments.This model can be used to analyze and predict the engineering performance of the ventilation duct,which is employed in the separated embankment of the Qinghai—Tibet expressway in the next 50 years.The results show that the two separated duct-ventilated embankments have a better cooling effect,and they can ensure the long-term thermal stability of the embankment and the underlying permafrost.However,when the separating strip width is less than 10 m,the characteristics of wind flow inside the duct of rear embankment are significantly affected by the separating strip width.This phenomenon causes an inferior cooling effect of rear embankment on underlying permafrost than the front embankment.In addition,a local warming effect occurs in the separating strip region between the two embankments when the separating strip is narrow.This effect could cause a serious thermal disturbance on the embankment and the underlying permafrost.The consequences include the declining of permafrost table,the rising of soil temperature and the asymmetry of temperature field beneath the embankment.A measure is made to weaken the local warming effect by connecting the ventilation ducts of two embankments.However,the thermal state of soils beneath the embankment and the separating strip region becomes worse after connecting,which indicates the failure of this method.