The Study On The Benefits Of Sand Fixation And Sand Resistance Of Four Types Of Sand Barriers Based On Three-dimensional Laser Scanning Technology

Land desertification has gradually become an important natural disaster problem globally,and wind erosion desertification is the key and difficult point in desertification control.Curbing the development trend of wind erosion and desertification and promoting man-land relationships’coordinated development has become an urgent choice and mission for people.Deserts surround the Minqin area.Every spring,yellow sand and dust raging scenes emerge endlessly.Actively combating wind erosion desertification can effectively prevent the two deserts of Badain Jaran and Tengger from converging and improving the Minqin ecological environment’s current state,it plays a vital role.Minqin is arid and lacks water,and plant sand control is restricted.The application and research of mechanical sand barriers play a considerable role in curbing the damage of regional wind and sand and the expansion of desertification.Therefore,field experiments on different types of sand barriers were carried out on the dunes of the Minqin desert area.Using three-dimensional laser scanning technology to observe the internal morphology of the sand barrier before and after the passage of high winds,collect sand samples and use the Malvern laser particle size analyzer to measure the characteristics of particle size changes.At the same time,combined with the wind tunnel experiment of the wind and sand environment;the research and analysis of the above characteristics can provide sand fixation and sand resistance benefit evaluation data for different types of sand barrier applications.The study results will provide theoretical support for the prevention and control of sand hazards in the desert-oasis transition zone and the prevention of the spread of desertified land.The main findings are as follows:（1）Through the analysis of the erosion status of the sand barrier,it can be found that the belt of PSB（Polylactic acid fiber sandbag sand barrier）has the lowest barrier height,and the erosion depth is the largest.The belt of SSB（Straw sand barrier）has the weakest erosion and the strongest accumulation.In the belt of CSB（Clay sand barrier）,erosion is concentrated in the middle,and the accumulation is on the sides of sand barrier;FSB（Fibermesh sand barrier）is the opposite.（2）Through the wind tunnel experiment to simulate the sand barrier wind and sand process,the internal erosion of the CSB is characterized by strong erosion and weak accumulation in the middle part and strong accumulation and weak erosion near the two sides of the sand barrier.FSB behaves opposite to CSB.Using three-dimensional laser scanning technology to calculate,it can be concluded that most positions in the PSB barrier are in a weak accumulation and strong erosion state,and the erosion volume is 6091 cm³,which is14.07 times the accumulation volume.It is basically consistent with the situation of field erosion.（3）Through the analysis of the soil particle characteristics of the sand in the sand barrier.The spatial distribution of the particle size components in the barrier varies according to the wind direction.The particle size of CSB gradually decreases from the center to sides.The particle size component of the SSB square format gradually increases from the center to the sides,and the upwind direction’s increase trend is slower than the other.The particle size of SSB and PSB row-belt types gradually increases along the main wind direction.The FSB and PSB grid patterns show increasing particle size from the middle to perpendicular to the main wind direction sides in the sand barrier and gradually decreasing along the main wind direction in the middle area.In the study,the CSB,SSB,and PSB row-belt types showed a trend of increasing particle size along the main wind direction.In the four types of sand barriers,the central value ofσis relatively high.The sortability becomes worse,which can also prove that the sand composition in the sand barriers is gradually increasing.（4）From the perspective of the change law of the particle size components of the sand dust in the vertical direction,the content of CSB and PSB coarse sand and medium sand gradually decreases with the increase in height,and the content of fine sand and magnificent sand gradually increases with the increase in height.The fine sand content in the upper layer reaches 62.35%.The content of magnificent sand of SSB and FSB gradually increased with the increase of height,and the content of fine sand gradually decreased with the increase of height.The four types of sand barriers all show an obvious trend that the particle size components of the sand dust gradually become smaller with the increase in height,and the finer particle size components occupy a major position in the higher height layers.（5）By measuring the wind speed of the sand barrier,it is clear that the average wind speed at each level of CSB and PSB gradually decreases from the bottom to the middle.Because the lower middle row-belt spacing of SSB is 1 m smaller than other parts,the wind speed is minimal,and the wind speed does not gradually decrease along the main wind direction.The wind speed changes in the FSB grid format gradually decrease along the main wind direction,and the wind speed of the middle belt sand barrier has a certain amplification effect.In the wind speed and flow field measurement in the wind tunnel,the CSB will have a wind speed slowing zone with one time the barrier height and 9 to 11.5 times the barrier height after the sand barrier,its mitigation effect is good.Right above the sand barrier,the wind speed increases rapidly with the increase in height,and a maximum value appears near 35 cm.In the PSB,there will be a wind speed reduction zone of 1 times the barrier’s height and 6 to 8 times the height of the barrier.The maximum value appears at the height of 20 cm and 5 cm behind the barrier.After the sand barrier,the FSB will have a wind speed reduction zone of 1 times the barrier’s height and 1 to 4 times the height of the barrier.The wind speed slowing areas all show that with the increase of wind speed,the slowing areas’area further decreases,wind speed slowing effect is average.（6）By studying the horizontal aeolian flux and the total amount of aeolian transported in the horizontal,segmented fitting is carried out according to the height of the impact of sand barriers.PSB shows that the horizontal aeolian flux gradually increases along the main wind direction.Except for PSB,CSB,SSB,and FSB,all show the smallest horizontal aeolian flux and total horizontal aeolian transport in the lower middle and middle parts maximum.After the impact range of the sand barrier is weakened,the four sand barrier coverage areas of the height layer are all fitted with exponential function fitting.The sand dust horizontal aeolian flux and total horizontal aeolian transport value of PSB and CSB are relatively large.The sediment transport capacity of PSB reaches 3,53.115 g·cm^-1,which is 45.06%higher than the maximum sediment transport capacity of CSB 1,935.548 g·cm^-1.It means frequent wind and sand movement,intense sand and dust activity,and poor sand blocking effect.To sum up the results of this research.,the four types of sand barriers have the following order of sand fixation and sand resistance benefits:SSB>FSB>CSB>PSB.However,combining its sand barrier changes,sand barrier material properties,maintenance costs,and staffing,and many other factors,the order of its sand fixation and sand resistance benefits may be:FSB>SSB>CSB>PSB.Three-dimensional laser scanning technology is introduced in the research to invert the micro-topography morphology in the sand barrier.It has the characteristics of high scanning accuracy,convenient operation and not affected by light.It can accurately measure the micro-topography erosion and accumulation volume and quantitatively analyze it—erosion level.At the same time,there are some shortcomings in this study.For example,the sand barriers are too new,and the effect of sand fixation and sand resistance may not be apparent.In the future,long-term observations can be used to study and analyze;the three-dimensional laser scanning technology needs to be further digging to control sand.Give full play to the field of geomorphology.