Evaluation Of Windproof And Sand-fixing Effect And Study On Mechanism Of Plant Protection Measures In Typical Wind-blown Sand Area Of Hetian-ruoqiang Railway

The total length of railway in China’s sandy areas is 15,000 kilometers,the largest in the world.Wind-blown sand disaster is the biggest obstacle to the construction and operation of the railway in the sandy area,and the prevention and control of wind-blown sand disaster is the top priority of the construction and operation of the railway in the sandy area.-Plant protection measures take into account both windproof and sandfixation and ecological benefits,so they have become an important option for the prevention and control of railway sandstorm disasters in sandy areas.However,there are relatively few systematic studies on the windproof and sand-fixing effects of plant protection measures under different underlying surfaces and wind speeds,which brings constraints to the in-depth promotion of related work.This paper adopts the method of field and wind tunnel test combined with simulation to study the windproof and sand-fixing effect of plant protection system under two geomorphic conditions of desert and Gobi in the severe wind-sand area along the railway.The relevant results can provide certain reference for the maintenance of plant wind-sand protection measures of Hetian-Ruoqiang railway.The main findings are as follows:(1)There is a good logarithmic relationship between wind speed and height in field test.The plant protection system played the role of windproof and sand fixation on the whole,and reduced the wind speed in different forest belts to different degrees.Meanwhile,the establishment of plant measures effectively reduced the wind speed within the canopy height.(2)The dynamic roughness under the influence of forest belts is analyzed.The increase of forest belts has a positive effect on the dynamic roughness.By comparing with the control point(open ground),it is found that the dynamic roughness increases continuously along the wind direction from the protection system to the railway approach area.(3)Through wind tunnel test,the spatial changes of wind velocity profile,sand transport rate and surface sand accumulation under the influence of plant sand control belt on Hetian-Ruoqiang railway were measured.It was found that the wind speed increased slightly below the height of the tree canopy when the air flow encountered plants.At the height of the canopy,the wind speed decreased significantly.Above the tree top,the air flow rises upward and the wind speed increases,forming a local acceleration zone.Under the same wind speed,along the flow direction,with the increase of the number of protection belts,the sediment transport rate gradually decreases.With the increase of incoming wind speed,the sediment transport rate of each measuring point increases.The shrub has a good protection effect on the near surface,which can make the sand deposit quickly.(4)The wind tunnel test showed that under 9m/s,12m/s and 15m/s,the windproof and sand fixing efficiency of the whole protection system decreased with the increase of wind speed: the sand prevention efficiency on the desert surface decreased from 88%to 78.5%,and the sand prevention efficiency on the Gobi surface decreased from 83%to 77%.(5)The numerical simulation of Fluent is used to study the protection effect under the condition of high wind speed.When the wind speed is 20m/s,the windproof effect of the protection system is more significant at 1m height,the wind speed can drop by up to 80%,and the sand material is basically deposited in the protection system.