Numerical simulation 0n the influence of different median strip types in the separated highway subgrade cross section on the transport law of wind-sand flow

To mitigate the sand burial of highways in sandy regions, a separated subgrade design was widely adopted in the embankments of high-grade highways, but the problem of sand deposition on subgrade slopes and pavements still happens frequently. Based on the theory of wind-sand two-phase flow, this paper constructed a three-dimensional model of the separated subgrade, the wind-sand flow transport law around the subgrade with varying median strip widths and concave depths was simulated by Fluent software. After comparison and analysis of seven subgrade models, the flow field distribution, wind speed horizontal variation, and erosion-deposition characteristics were investigated. The findings are as follows: (1) The width of the median strip in the separated subgrade had significant influences on the wind-sand flow. The smooth passage of wind-sand flow over the road surface was facilitated with the increase of the median strip width. However, sand deposition in the median strip happened. It can lead to secondary sand damage of downwind subgrade and increase the work load of road sand removal for subsequent maintenance. (2) The obstruction to airflow and sand accumulation was aggravated with greater concave depth of the median strip. Therefore, it is advisable to minimize the concave depth of the median strip in case of more sand damage. (3) A median strip width exceeding 12 m (possibly without guardrails) for an integral embankment without enough road land is recommended. Conversely, median strip width of over 40 m for separate subgrade with unrestricted land is suggested. (4) In the case of sand deposition in the existing separated subgrade, the median strip can be filled by sand deposition or other materials, then was covered with gravel to form a flat ground like Gobi smooth surface, which can let the wind-blown sand flow pass through the subgrade section without sand deposition.