青藏铁路沱沱河路段流场特征及沙害形成机理

Study on the Characteristics of Flow Field and the Mechanism of Wind-blown Sand Disasters in the Tuotuohe Region along the Qinghai-Tibet Railway

通过对青藏铁路沱沱河路段路基流场结构、风速廓线特征的风洞模拟实验研究,发现气流在途经铁路路基时,路基断面对近地表流场改变极大,在其两侧形成明显的遇阻抬升区、集流加速区、减速沉降区以及消散恢复区。铁路沙害的形成主要是路基迎风侧气流由于遇阻抬升和集流加速,对路肩和路基中上部产生风蚀;随着气流加速抬升,底层砂粒以跌落沉降的方式堆积在路基迎风坡坡脚,造成路基沙埋;当气流越过路基,在背风侧由于减速沉降和涡旋运动,风沙流处于过饱和状态,将所携带的大量砂粒堆积在背风坡。

Qinghai-Tibet Railway, with an average altitude of 4 500 m a. s. 1. , high-altitude region in the world. It passes through 550 kin-long permafrost belt and is the longest railway in the crosses the Kunlun Mountains and Tanggulha Mountains on the Qinghai-Tibetan Plateau. Based on the wind tunnel experiment of flow filed structure and wind profiles around the railway bed along the Tuotuohe section of the Qinghai-Tibet Railway, it is eonsidered that a section of railway bed will obviously change the pattern of flow field near ground surface, and there are the obvious blocked-rising area, collected-accelerating area, decreased-depositing area and diffused-restoring area of airflow in a flow field. The mechanism of wind-blown sand disaster formation along the railway is mainly as follows ： wind erosion occurs at the railway shoulder or the mid-upper part of railway bed because airflow at windward slope is forced to lift and accelerate ; sand grains in the bottom layer deposit at the toe of windward section and bury the railway bed as airflow is enforced to lift; wind-blown sand is in a supersaturation state and accumulates at leeward slope of the railway bed because of the wind speed decrease and eddy motion when airflow gets across the railway bed. The Qinghai-Tibet Railway is destined to suffer from wind-blown sand disasters. With climate change and increase of human activities, the occurring frequency of wind-blown sand disasters along the railway will increase in the future. In a word, it has become a new challenge for both government and scientists how to control wind-blown sand disasters along the Qinghai-Tibet Railway in an effective and scientific way.