束流型拦砂坝溢流口及其关键参数确定

Experimental investigation on the lateral contraction spillway and its key parameters determination

为进一步优化拦砂坝溢流口体型,确定溢流口几何参数取值,通过物理模拟实验研究了不同拦砂坝溢流口体型条件下泥石流过坝的流态、坝后冲刷深度、消能率变化规律,并根据拦砂坝埋深设计标准与松散体水下临界平衡关系,探讨了溢流口收缩率的合理取值范围,结果表明：采用斜面或者大倾角的反弧型溢流口时,坝后泥石流落点与坝脚的距离近、冲刷深度大,而采用无倾角的反弧型溢流面时,不仅可以在一定程度上减小冲刷深度,而且大大增加了坝后泥石流落点与坝脚的距离;在泥石流规模与溢流面曲率半径相同情况下,适当增大侧向收缩率,有利于增强泥石流体与坝后动床之间的相互作用,提高泥石流通过坝后冲刷坑的消能率;当溢流口收缩率在0.2～0.6之间时,冲刷深度满足设计要求,且泥石流跌落点距坝脚较远,冲刷坑发展不会危及坝体安全。

In order to modify the spillway structure of a check dam and specify the geometry parameters of the spillway,the debris-flow pattern,scour depth,and energy dissipation were discussed under the conditions of different bottom surfaces and lateral contraction ratios based on physical modeling experiments. According to the buried depth design criteria for check-dam foundations and critical equilibrium for nonviscous particles under water,the rational value of the lateral contraction ratio was also discussed. The results indicated that the scour hole with deep scour depth was near the dam foundation when the spillway surface was a plate or curved surface with a large inclined angle. When a curved surface with a horizontal outlet was considered,not only was the scour depth decreased to some extent,but the distance between the plunging point and the dam toe was also enhanced. Generally,upon increasing the lateral contraction ratio,the energy dissipation rate increased due to the stronger interaction between the debris flows and erodible bed downstream if the debris-flow scales and spillway curvature were fixed. When the lateral contraction ratio was in the range 0. 2—0. 6,the scour depth behind the check dam satisfied the engineering design. Meanwhile,the distance between the plunging point and the dam toe was reasonable. This study can provide some reference points for the design of debris-flow mitigation in the engineering of check dams.