机械防沙体系防沙功能的衰退过程

作为一种十分有效的防治流沙的方法，机械防沙体系在防止风沙前移显示出很大的优越性，其目的就是要把流沙滞留在体系内，体系在发挥其功能的同时也是逐步丧失其功能的过程。在平坦地形条件下，草方格沙障积沙是从前沿向纵深发展的。在复杂地形地貌条件下，流沙的堆积具有不平衡性，且积沙形式多样。无论积沙形式如何，都有整体向前推进的趋势。阻沙栅栏的积沙形式因材料及孔隙度的大小而异，阻沙栅栏在初期时，可以拦截较多的沙量（75%），草方格固沙带只承担25%的积沙量，随着时间推移，阻沙栅栏的效益逐渐降低，草方格固沙带则要承担较多的积沙量。从阻滞的沙量来看，一道栅栏阻拦的沙量至少等于40行草方格滞留的沙量，在工程实践中应优先考虑栅栏的应用。

Decline Mechanism and Process of Mechanical Defense System

Sand damage control has always been a matter of common concern in the desert regions worldwide.Mechanical defense system is a compound sand damage control measure constituted by straw checkerboard barrier and high sandbreak palisade.It is a very effective measure and its purpose is to detain shifting sand in the system.As the system exerting its function,its function is declining gradually.The sand deposition forms differ greatly with the landform.On the flat landform,the progress of sand deposition in the straw checkerboard barrier pushed from the front edge to backside.On complex landforms,shifting sand deposited asymmetrically on the straw checkerboard barrier and has several sand deposition forms.Regardless of sand deposition forms,they have the trend to push forward integral.Sand deposition forms of high sandbreak palisade are different according to the porosity and the material that made it.At the initial stage,the palisade can intercept more sand than straw checkerboard barrier.With the lapse of time,the sand block effectiveness of palisade gradually declined and the straw checkerboard barrier bear more sand depositing.From the sand deposition amount,one high sandbreak palisade action is equal to 40 rows of straw checkerboard barrier at the least.So it must give priority to the palisade in establish of the mechanical defense system.