Study On The Characteristics Of Wind And Sand Flow In Different Mechanical Sand Barriers

Wind sand transport is a major form of wind and sand movement that occurs in arid and semi-arid desert areas.The sand particles move with the wind under the action of wind to accelerate the process of land desertification.Hazards have now aroused widespread concern in various countries.Mechanical sand barrier,as a kind of desertification control measure widely used in the field of desertification control,has a significant effect on stabilizing quicksand.In this paper,six types and specifications of mechanical sand barriers(1.5m×1.5m wheat straw sand barrier,1 m×1 m wheat straw sand barrier,1.5m×1.5m PLA sand barrier,1m×1 m PLA sand barrier,1.5m×1.5m mixed sand barrier,1m×1m mixed sand barrier)are laid on the mobile sand dunes around the Oasis Desert Transition Zone on the southeast edge of Tengger Desert.Based on the field observation and indoor test,different winds are analyzed Under the condition of velocity gradient,the structure characteristics of near surface wind sand flow,the particle size composition of sand carried by the air flow and the form of sand moving with the wind under the influence of mechanical sand barrier.The results show that:(1)The wind speed in the wilderness increases exponentially with the height,and the total sand transport rate is in the order of bare sand dune,PLA sand barrier,mixed sand barrier and wheat straw sand barrier from large to small,and the total sand transport rate increases with the increase of sand barrier specification,and with the increase of wind speed,it is quadratic polynomial,the increase range is: 1.5m×1.5m specification > 1m×1m specification;bare sand dune > PLA sand barrier >mixed sand barrier > wheat straw sand barrier.(2)The sediment transport rate of each layer has a negative correlation with height and a positive correlation with wind speed,andthe law of its increasing range is the same as that of the total sediment transport rate with wind speed.The height of sand transport activity is directly proportional to the wind speed,and the order from high to low is wheat straw sand barrier,mixed sand barrier and PLA sand barrier.The function model of vertical variation of sediment transport rate with height is related to wind speed and underlying surface properties.(3)In 0-24 cm height,bare sand dune(control),1.5m×1.5m PLA sand barrier,1m×1m PLA sand barrier,1.5m×1.5m wheat straw sand barrier,1.5m×1.5m mixed sand barrier,1m× 1m wheat straw sand barrier and 1m ×1m mixed sand barrier account for 92.77%,81.82%,81.41%,71.38%,70.29%,63.94% and 58.21% of the total sediment transport respectively.The cumulative sediment transport increased with the increase of height in seven plots,among which the change rate of bare sand dune was the largest and that of 1 m×1 m mixed sand barrier was the smallest.With the increase of wind speed,the cumulative sediment transport rate of seven samples in the underground layer increased,and the other six samples decreased except for the bare sand dunes in the upper layer;with the increase of sand barrier specification,the cumulative sediment transport rate in the lower layer increased,and the cumulative sediment transport rate in the upper layer decreased.(4)Fine sand is the main sand in the air flow of seven kinds of plots.The grain size distribution of wheat straw sand barrier has no obvious change rule with the wind speed.The grain size distribution of the other five kinds of plots has the same change rule under different wind speed gradients,which is shown as: fine sand > medium sand > very fine sand >Coarse Sand > silt.(5)The content of silt and very fine sand in seven plots was positively correlated with height,negatively correlated with wind speed and sand barrier specification,the content of wheat straw sand barrier was the most and bare sand dune was the least;the content of medium sand and coarse sand was negatively correlated with height and positivelycorrelated with wind speed;the content of fine sand was positively correlated with sand barrier specification,and had no obvious change rule with height and wind speed.(6)The average grain size of sand in the air flow of seven plots was2-3.6 ?,which was positively correlated with the height and the size of sand barrier,and negatively correlated with the wind speed.The particles in the air flow were wheat straw sand barrier,PLA sand barrier,mixed sand barrier and bare sand dune from fine to coarse.From bad to good,the order of sorting performance is wheat straw sand barrier,mixed sand barrier,bare sand dune,PLA sand barrier.The larger the sand barrier specification,the better the sorting performance.The deflection values of six kinds of mechanical sand barriers are negatively correlated with the height and the average particle size(?).The peak degree is medium and narrow,which is positively correlated with the average particle size(?).It increases with the increase of wind speed and height,and decreases with the increase of sand barrier specification,which is shown as wheat straw sand barrier > mixed sand barrier > PLA sand barrier > bare sand dune.(7)The movement forms of sand in the air flow of seven plots were mainly saltation,followed by suspension and least creep.Among them,the suspension content of wheat straw sand barrier is the most,the jump and creep content is the least.There was a positive correlation between the suspension content and height,and a negative correlation between the jump and creep content and height.