Combined Action Mechanism Of Ulan Buh Desert Sand Prevention Technology Measures And Its Optimal Configuration

Engineering measures as the basis for sand and the necessary conditions for biological measures,it is widely used in road,railway and urban areas such as sand damage control,different measures to prevent sand complex mechanism of action and effective protection to determine the scope of the protection system structure design optimization is important.In this paper,through the wind tunnel experiment of different sand prevention technology measures,single and superimposed sand prevention measures in different directions of wind speed gradient horizontal airflow velocity field variation and vertical airflow velocity profile changes characteristics,analysis of the vertical sand flow around the measure and the surrounding sand blocking effect,the complex action mechanism of different sand prevention measures was discussed,and the compounding action law was verified in the field,and the different modes of sand prevention damage prevention were optimized with the economic cost.The results show that:(1)Different measures near-surface air flow with the horizontal distance are showing a "first to reduce,gradually stabilize,increase after" trend,and this variation is not interference by the indicative wind speed,but the air flow changes significantly inflection point difference.-10H is the point of air flow fluctuations,-5H is the inflection point of wind speed reduction,the airflow tends to stabilize the inflection point is different,the overall performance of the smaller the size,the higher the height of the air flow stability faster,the inflection point position more forward,while the effective protection of the leeward side.-4H and-2H is the point of air flow fluctuation and wind speed reduction with a single sand barrier respectively,and its air flow tends to be short.Double-row sand barrier windward side air flow changes the same inflection point and a single sand barrier,air flow into the sand barrier between gradually stabilized,after a certain distance from the leeward side began to recover.When the sand barrier superimposed in different ways,did not change the air flow in the windward side of the variation,"narrow front wide back" and "resistant front consolidated back" mode increases the distance of the air flow stable region,which extended airflow recovery point position,"high front low back”mode and double-row sand barrier difference was not significant.(2)The airflow velocity profiles at different positions on the windward side of different measures are not significantly affected by obstacle,the leeward side of the air velocity profile changes significantly different inflection points.Checkerboard barrier and single sand barrier leeward side near the surface 0?4cm height significantly reduced airflow,4-16cm airflow uplift significantly,4cm height of the inflection point of rapid changes in wind speed.Double-row sand barrier enhances the control of the near-surface air flow,8cm height of the inflection point of rapid changes in wind speed.When the superposition of different sand prevention measures to reduce and uplift the role of different heights appear different wind speed,4cm height is "resistant front fixed back"mode wind speed sharply reduced inflection,8cm height is "high front low back" and"narrow front wide behind" mode wind speed sharply reduced inflection,showing a variation of the upward movement of the inflection point with the increase of the height of the sand prevention measures.All modes indicate changes in wind speed only affect the scale of wind speed changes,does not affect the vertical air velocity profile changes.(3)The model is placed after the wind tunnel,the wind side of the sand flow structure is basically similar to the hollow,90%of the sediment concentration is mainly concentrated in the 0?10cm height layer,the change of the vertical height leeward side with the sand is no longer follow the law of sand flow structure,and there is a significant power function relationship between sediment transport and wind speed at different levels.Due to the different measures of each layer height sediment concentration changes,the overall performance of the higher the height,the more the total amount of sand lost less superimposed,and the concentration of sediment gradually moved upward,and the height of the peak from 8cm to 16cm height,10cm?20cm and 20cm?30cm height layer the proportion of sand transport is gradually increased.(4)Measures to prevent sand two-dimensional space surface area of sand directly reflects the potential scope of the measures of wind interference range and plot of sand,sand blocking effect indirect reflection of sand-proof measures,sand-proof measures three-dimensional space directly reflects the amount of sand blocking effect of certain sources of sand,sand-proof measures under wind conditions,both 0.15m height 1.5m×1.5m specifications and 0.15m height 2mx2m specifications,single-row sand barrier and 12H row spacing of the double row sand barrier sand barrier effect were poor.After the combination of different measures to each other significantly enhanced sand blocking effect,under different conditions indicating the wind speed,three lines of sand barrier sand barrier range of about 1.51 times the double-row sand barrier,sand blocking capacity of about 2.18 times the double-row sand barrier,"resistant front consolidated back" type superposition mode compared with the same size square sand barrier sand range increased by an average of 32.18%,the amount increased by 17.12%.(5)The composite effect model and the prediction results show that the effective protection distance difference between the near-surface wind speed of different sand prevention measures is significant,the smaller the size,the higher the height,the more the number of sand prevention measures the more complex effect is obvious.Different single measure after superposition,its effective protection range doubled,double-row sand barrier than single-row sand barrier effective protection distance increased by about 13H,three-row sand barrier than single-row sand barrier increased by about 28H.The reasonable "high front low back" superposition pattern and contour pattern difference is not significant,"narrow front wide back" mode significantly increased the effective protection of high vertical sand barrier distance,"resistant front fixed back" mode significantly increased the composite effect of the grid sand barrier,near-surface air flow stabilized speed significantly faster.Combined sand resistance and field measurement results,0.15m height 1.5m×1.5m and 2m×2m specifications,80cm height below the single-row sand barrier and 12H row spacing double-row sand barrier wind effect is weak,0.2m,0.3m height 1m×1m specifications and 4H line spacing double line sand barrier and similar specifications wind effect difference is not significant,are not recommended,other measures can be superimposed on each other to choose to use.(6)Ulan Buh Desert Sand damage control system should be established engineering and vegetation combination of integrated sand prevention system,which should be combined with the local sand control system in wind and sand environmental characteristics select "dense front sparse back" and "dense outside sparse inside"configuration mode,"high front low back" type two lines and the "narrow front wide back" type three lines and other sand damage prevention mode,according to the degree of sand damage superimposed with each other to establish a "leading edge sand blocking zone,combination of fixing and resistance,sand fixation belt" consists of "resistant front fixed back,consolidation and resistance combination" comprehensive protection system.