## 5 Conclusions  
On the basis of the field measured data and CFD numerical simulation, this paper studied the structure of the wind-sand flow field and the distribution law of sand accumulation around highways in different terrain environments in the drifting dune area under different wind speeds, and mainly drew the following conclusions:  
1. Long-term wind action can make dunes move along the dominant wind direction, forming sand burial on the highway, thus affecting the normal operation of the highway. 2. The existence of dunes would affect the flow field structure and sand-accumulation position around the embankment. The airflow velocity gathers to the maximum at  
Figure 14: Sand accumulation of the highway in flat terrain (**a**) distribution of sediment (**b**) vertical measurement. Figure 15: Sand accumulation of the highway on the dune’s windward side (**a**) sediment distribution in October 2020 (**b**) sediment distribution in April 2021 (**c**) scale measurement. the top of the dune. The airflow velocity changes in different wind speeds of the same highway structure are basically consistent. 3. For each point on the subgrade section, the airflow velocity at the junction of dune and subgrade decreases the most and it is easy to form sand accumulation. However, under the condition of low wind speed, dunes hinder the sand-carrying wind, and the airflow velocity decreases below the sand-driving wind on the windward slope of the dune, resulting in the deposition of most sand grains. 4. For the highway in the drifting dune area, the wind energy environment change trend should be studied in detail, sand protection should be set on the dominant wind direction side to control the dune movement speed, and the sand-accumulation situation on the highway should be checked regularly to clear the sand accumulation in time. In practical engineering, highway sand accumulation is affected by wind direction, quicksand intensity, and construction technology. This study mainly focused on the formation mechanism of sand accumulation of subgrade in the initial state under ideal conditions of single wind direction and constant wind speed. However, in practice, highway sand accumulation is affected by a variety of factors. Our research results and conclusions provide a preliminary reference for practical engineering. In this paper, the observation time of meteorological data for the analysis of wind-sand activity along the line was short, so that the sand transport potential in the observation area was similar to the calculation results of previous scholars; however, there is a gap. If a long-term wind-sand monitoring system can be established to increase the time span of wind-sand monitoring data, the characteristics of the wind-sand environment can be evaluated more accurately. For different desert road structure types, the degree of damage caused by wind-sand disaster is also different. The same road structure is used in field experimental observation and wind-sand flow simulation. In order to more accurately analyze and discuss the vulnerability of desert roads, it is appropriate to consider a variety of road structure forms in subsequent research. Our research methods and results can be extended to the construction of desert highways and the construction of sand prevention systems for roads in mobile dune areas to reduce sand hazard. Conceptualization, F.H. and Z.L. ; methodology, F.H. and Z.L. ; software, C.W. and Z.L. ; validation, W.Y. ; formal analysis, F.H. and L.L. ; investigation, L.L. ; resources, L.L. and W.Y. ; data curation, C.W. and Z.L. ; writing--original draft preparation, Z.L. and C.W. ; writing-review and editing, C.W. and Z.L. ; supervision, F.H. and L.L. ; project administration, F.H. ; funding acquisition, F.H. and W.Y. All authors have read and agreed to the published version of the manuscript. This work was supported by the National Natural Science Foundation of China (grant numbers 51568037) and the Science and Technology Project of Ningxia Transportation Department (grant number 20200173).