| check dam is an important measure of soil and water conservation created by the people in the Loess Plateau,but the problem of water damage of check dam has been hindering the development of check dam.According to the investigation,spillway plays an important role in reducing the water damage of check dam,but the general and proportion of spillway in check dam is relatively low.Except for backbone dam and a few medium-sized check dams,other projects are not The main reason for setting up spillway is that the fund ratio of check dam spillway is insufficient.In order to popularize the spillway in the construction of check dam,it is necessary to study a new type of spillway which is cheap and suitable for the construction of check dam.After putting forward the concept of flexible spillway of check dam for the first time,the research group completed the small scale model test of flexible spillway of check dam,which proved the feasibility of the concept.On the basis of the above research,this paper summarizes two kinds of flexible stepped spillway,U-shaped geobag stepped spillway and thin-walled flexible stepped spillway,which are suitable for the construction of check dams.The strength test of the flexible lining(CADSS)is carried out by the electronic universal machine.The geotextile reinforced soil slope is introduced into the slope reinforcement of the U-shaped geotextile bag type flexible stepped spillway,and the best reinforcement method is studied by stab software.Based on the analysis of the overall stability performance of the U-shaped geobag type flexible stepped spillway after the discharge test,the U-shaped geobag type flexible stepped spillway is improved to a thin-walled flexible stepped spillway with wider application conditions.Two experimental schemes of broad crested weir flow and gate outlet flow are designed to explore the law of energy dissipation rate and flow pattern change of flexible stepped spillway,and the overall structural stability of the spillway after passing water is compared by using UAV scanning three-dimensional terrain,which proves that the new flexible stepped spillway can be extended to the actual danger removal and reinforcement project.The main research contents and achievements of this paper are as follows:(1)In this paper,two sets of flexible stepped spillway models are summarized through experiments,and the feasibility of the two models is proved in the actual model making.U-shaped geobag type flexible stepped spillway is suitable for building on the small check dam with low flood standard,and its technology is relatively simple;the thin-walled flexible stepped spillway has a wider range of use,and the side wall of the spillway can adjust the side wall slope ratio according to the stability requirements of the actual project,so the stability of the side wall is higher.The strength test of the flexible lining material(CADSS)shows that its strength is far greater than that of the traditional geotechnical composite material,which meets the needs of the flexible lining.The geotextile reinforced slope is introduced into the slope reinforcement of U-shaped geotextile bag type flexible stepped spillway,the stability of the slope after reinforcement is improved,and the allowable value of the spillway slope safety is met.(2)Through the analysis of the video recording of the discharge test process,the flow pattern under the weir flow condition is transition flow when the head on the weir is greater than 45cm,and drop flow when the head is less than 45cm;under the gate outlet flow condition,the head on the weir is constant at 15cm,and the flow pattern is drop flow.The results are consistent with the empirical formula for distinguishing the flow pattern of rigid spillway.The flow pattern of flexible stepped spillway is determined by the water depth nearby(the ratio of head on weir to height of step).(3)According to the comparison and analysis of the deformation data of the spillway before and after the discharge test,the stepped spillway itself undergoes slight deformation and absorbs energy after being impacted by the water flow,so the energy dissipation rate of the flexible stepped spillway is larger than that of the rigid stepped spillway,and the energy dissipation rate of the flexible stepped spillway is greater than 89%in the downflow state,and 73%-82%in the critical flow state,The difference lies in the location and quantity of multi-stage hydraulic jump.In order to ensure a high energy dissipation rate,in the subsequent design of flexible stepped spillway,the spillway width can be appropriately increased to reduce the water head on the weir or increase the height of single step.(4)Under the condition of weir flow,the energy dissipation rate of flexible stepped spillway decreases with the increase of weir head,and the variation range is large.Under the condition of gate outlet flow,when the weir head is fixed,the energy dissipation rate of flexible stepped spillway decreases with the increase of weir flow velocity,but the variation range is small,so the main factor affecting the energy dissipation rate is weir head,while weir head mainly affects the flow Therefore,the energy dissipation rate of flexible stepped spillway is mainly determined by the flow pattern.(5)There are 17 steps in the model of flexible spillway,and 4 velocity measurement sections are respectively located on the weir,the 6th step,the 12th step and the dam foot.The four sections divide the spillway into the front,middle and back three energy dissipation rate measurement sections.The energy dissipation rate of the front,middle and back flexible stepped spillway tends to decrease,and then decreases after the energy dissipation rate reaches the maximum in the front section of the spillway.The energy dissipation rate of the middle and back sections of the spillway tends to decrease slightly.The main reason is that the flow velocity in the front section is low,the water flow strikes the lower steps sufficiently,and the energy dissipation is large;because of the increase of the flow velocity in the middle and rear sections,some of the water flow strikes the lower steps,and some directly crosses the lower steps,the energy dissipation is insufficient.When the flow pattern is downflow,the energy dissipation rate of the spillway increases with the increase of the number of steps.When the flow pattern is transition flow,the energy dissipation rate of the spillway increases first and then decreases with the increase of the number of steps.(6)Under the condition of weir flow,when the water head on the weir is greater than 45cm,the energy dissipation rate of flexible stepped spillway increases first and then decreases with the increase of the number of steps.The reason is that the flow pattern is transition flow.At the end of the spillway,the flow has multi-stage hydraulic jump,resulting in the decrease of energy dissipation rate of the spillway.When the head of water on the weir is less than 45cm under the conditions of gate outlet and weir flow,the energy dissipation rate will always increase with the increase of the number of steps... |
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