Investigations into the law of sand particle accumulation over railway subgrade with wind-break wall.

Windbreak wall over railway subgrades is an effective and widely used measure to reduce the impact of high-speed wind in northwest China and central Asia. For the railway crossing sandy/Gobi desert, there exists serious sand accumulation over subgrade behind windbreak walls, causing great harm to the normal railway operation. So far, many measures have been tried to prevent sand accumulation. However, due to lack of understanding on causes of sand accumulation, they are often ineffective. To explore the characteristics of wind-blown sand flow around railway subgrades and the causes of sand accumulation, we set up a turbulent flow-sand particle-terrain coupling model and calculated sand particles' motion features around a typical windbreak wall in Lanxin railway line using the Lagrangian particle-tracing model. The results show that in sandy desert, although inflow sand particles are difficult to fly over windbreak wall, due to presence of a large reflux zone behind the windbreak wall where "reverse" wind-blown sand flow is generated, sand particles are blown up and rolled back to the subgrade under the effect of vertical wind velocity and reflux. By contrast, in the Gobi desert, sand particles are much easier to fly over windbreak wall and possess different motion features under different wind speeds. To solve the problem of sand accumulation on railway subgrade, we should comprehensively consider both wind speed and underlying conditions and then take appropriate measures.