Testing Research About The Stepped Flexible Protective Surface On The Overflow Earth Dike

The crucial part of overflow earth dike is erosion prevention for flowing surface. For the earth dikes which are built with clay and silty clay and some are built on the soft ground, in view of the big distortion of dam ground and the dams, we consider taking geomembranes which can adapt big distortion to protect the flowing surface.In this paper, the investigation about water releasing on the stepped flexible bottom spillway model whose bottom was made by geomembrane bags was tested. At the same time, we studied the characteristics and regularities on the water depth, velocity, rate of energy dissipation in this special structural spillway. The test result indicated:â‘ In the same flow discharge, the energy dissipation of the stepped flexible bottom spillway is more effective than the normal flat bottom spillway. The stepped spillway reduces the velocity of flow, but the rate of energy dissipation is decreasing with increasing of flow. It shows that when the flow is larger, the rate of energy dissipation on the stepped spillway is decreasing in the all water energy, and therefore the stepped flexible facing is more proper to the condition of small flow.â‘¡When the stepped flexible bottom spillway is releasing water, the velocity, energy dissipation,the dam surface roughness and water surface line are affected by the height of steps and the horizontal length. When the height of steps is the same, the longer horizontal length is, the larger rate of energy dissipation is.Through the experimental investigation of flowing surface destruction, the range and conditions of destruction which was made by the sharp-pointed detritus, the remainder of concrete and floaters which were flowed with released water were analyzed, the result showed that:â‘ The damage range of geomembrane bags which are made by the sharp-pointed detritus, the remainder of concrete and floaters is concentrated in the half of lateral revealable part in small flow, and is concentrated in the one third part of the lateral revealable part in lager flow in this experiment;â‘¡The damage forms of floaters are triangle shape in general case, but the damage forms of the sharp-pointed detritus are mostly round hole; and the round hole has greater influence in the quantity of lost soil than triagle sharp and other forms of damage;and the damaged geomemebrane bags will be filled with water and elevate the water surface line.Through the experiment we also found that: using the measures of geomembrane protective"hats"can avoid destroying on the bag surface and can effectively protect the soil loss amount in geomembrane bags which have already damaged, and the more obvious protective effect is ,the larger the thickness of the protective"hats"is.Some advertent problems and advices about the practical application of protection by flexible geomemebrane bags were put forward in this paper.