青藏铁路路基对风沙运动规律影响的数值模拟

Numerical Simulation on the Influence of Subgrade of Qinghai-Tibet Railway on Wind-Sand Movement

【目的】通过Fluent软件进行模拟计算,研究青藏铁路原有路基及新提出的一种输沙型路基的流场分布情况以及路基积沙特征,并讨论了轨枕式挡沙墙与PE阻沙网对路基风场及积沙特征的影响,探索路基对风沙运动规律的影响,为青藏铁路防沙治沙提供理论基础。【方法】采用数值模拟的方法,选择3种路基(普通路基、通风路基、输沙路基)以及2种沙障(轨枕式挡沙墙、PE阻沙网)的组合形式,通过模拟流场及积沙分布特征,评价沙障的防沙效果并分析路基受风蚀影响的程度。【结果】3种路基的风速流场具有相同的功能分区,且风速对流场的影响较小;在路基迎风侧,普通路基对风速的降低作用最强,极易引起沙粒在路基坡脚和边坡堆积,路基顶部风速明显增加,大风时可能会影响行车安全,路基背风侧存在回流现象,部分沙粒在重力作用下会堆积在背风侧边坡处;普通路基迎风侧边坡积沙情况严重,沙埋铁轨现象频发,布设有通风管的路基会受到积沙影响,导致管道堵塞,影响其冻土保护功能,输沙路基利用狭管效应,使风沙流加速通过,防止迎风侧边坡积沙和风沙上道,且一旦输沙管道发生积沙,可通过自然风力清除,若必须人工清理也便于操作,可节省大量人力物力;当路基上风向布设沙障时,沙障对风速有极强的减弱作用,路基和沙障之间存在一个减速区,该区域速度呈中间大两端小分布规律,风速无法达到起沙风速,沙粒沉积在沙障前后,路基边坡积沙明显减少。【结论】3种路基在无防护措施情况下,均有不同程度的积沙,输沙路基积沙量最小,且便于清理;轨枕式挡沙墙积沙量迎风侧大于背风侧,PE阻沙网积沙量背风侧大于迎风侧,并且沙障间距影响着阻沙效果,适当调整沙障间距,使此区间内的风速不足以起动沙粒,提高沙障阻沙效果;模拟结果表明,输沙路基相对于普通路基和通风路基更适用于风沙地区,但目前的结果还停留在理论阶段,需要在高原环境中进一步进行试验验证。

【Objective】 Qinghai Tibet railway is an important link in the development of the western region of China.As a result of the special natural environment,the frequent occurrence of wind sand disaster has become one of the most important factors affecting the safe operation of the railway. In this study,we used the Fluent software to simulate the different types of Qinghai-Tibet railway subgrade with sand barrier layout and analyzed its wind speed flow field and sediment characteristics. Our aim is to provide a theoretical basis for reasonable layout of sand prevention measures to reduce the accumulation of sand in the subgrade and is to ensure the safe operation of the railway.【Method】 With the numerical simulation method, three kinds of subgrade（Ordinary subgrade, Ventilated subgrade, Sand-transmitting subgrade） and two sand barriers（Sleeper typed retaining wall,Sand blocking PE nets） combinations were selected to simulate the flow field and sand distribution,for evaluating the sand prevention effect of sand barrier and analyzing the affecting extent of the subgrade by wind erosion.【Result】 Simulation result show that the wind speed field of three types of subgrade all had the same functional partition,and the wind speed had little effect on the flow field. On the windward side,the effect of ordinary subgrade on reducing wind speed was the strongest. Sands were easy to accumulate on the slopeand the foot of the slope. The wind speed was significantly increased at the top of subgrade which may affect traffic safety.There was a reflow phenomenon at leeward,leading to the accumulation of sands on the leeward slope under gravity. The sand accumulation on the windward slope of common subgrade was serious and buried rail frequent. The ventilated subgrade would be affected by sand sediment, limiting the permafrost protection. The sand-transmitting subgrade prevented sand accumulation on the windward slope and rail. Once the occurrence of sand deposition on the transport pipeline,could be removed by natural wind. It was also easy to clean up and save a lot of manpower and resources. When the sand-break wall laying before the subgrade,the sand-break wall on the wind speed had a strong weakening effect.There was a deceleration zone between the subgrade and the sand-break wall,the wind speed could not reach the sanddriving wind speed. Sands deposited before and after sand-break wall,the amount of sediment accumulation on subgrade slope was greatly reduced.【Conclusion】Three kinds of subgrade in the absence of protective measures,there are different degrees of sand accumulation. The amount of sediment of sand-transmitting subgrade is minimal,and easy to clean up.The sand accumulation of Sleeper typed retaining wall on the wind side is greater than the leeward side. The sand accumulation of Sand blocking PE nets on the leeward side is greater than the wind. The spacing of sand barrier affects the effect of sand blocking. Appropriate adjusting sand barrier spacing to improve sand blocking effect. According to the simulation,the sand-transmitting subgrade is more suitable for the sandy area. However,the result are still in the theoretical stage and need to be further tested in Plateau environment.