土石流防治工法之梳子壩開口寬度設計模式

Design Model on opening Width of Slit Dam for Debris Flow Control

10.29417/JCSWC.199809_29(3).0001

連惠邦(Hui-Pang Lien)；柴鈁武(Fang-Wu Tsai)

梳子壩 ； 囚砂率 ； 泥砂體積濃度減少率 ； 開口寬度 ； slit dam ； trap efficiency ； rate of reduction in volumetric sediment concentration ； opening width.

中華水土保持學報

29卷3期（1998 / 09 / 01）

175 - 187

繁體中文

梳子壩透過壩體開口寬度的適當調整，可以有效降低土石規模的論已被提出，惟針對不同地形條件及防治效率，其開口寬度的殴計方法卻一直未被完整地建立。因此，本研究透過理論推導及渠槽試驗，發展梳子壩與土石流間之土砂互動模式，以及其開口寬度之設計模式。研究結果顯示，壩體囚砂率與土石流泥砂體積濃度减少率兩無因次參量，可反應土石流經梳子壩攔擋之後，其泥砂體積濃度和攜出土砂數量的減少程度，即P=1-λ((1-R)(1-C_(da)/1-(1-R)C_(da)) 式中，P=囚砂率;R=泥砂體積濃度減少率;C_(da)=土石流臨前泥砂體積濃度;λ=水體流出比（≈0.9）。上式顯示土石流與梳子壩間的土砂互動規律與壩體相對開度，狹縫密度及臨前泥砂體積濃度等因素相關。在工程應用上，本研究結合臨前泥砂體積濃度，囚砂率及泥砂體積濃度減少率等方程式建立了梳子壩開口寬度的一般設計模式，使在不同的地形條件及囚砂率之下，可以簡便地設計出其對應之壩體開口寬度。同時，基於下游被保全地區之安全考量，而要求梳子壩必須具備轉化土石流成為較無危害性的一般挾砂水流時，其壩體開口寬度之安全設計模式及線解圖亦已建立，可以提供工程設計之參考。

It has been proposed that with appropriate adjustment of the opening width, slit dams can effectively reduce the scope of debris flow disaster. However, no method has been established for the design of the dam opening width that can be applied to different geological structures and trap efficiency. Using theory deduction and flume experiments, we developed a model that simulates the mutual movement of the sediment between a slit dam and a debris flow as well as a model that designs the opening width. The results indicate that the dimensionless parameters of the dam trap efficiency and the rate of reduction in volumetric sediment concentration in a debris flow can reflect the volumetric sediment concentration and the reduction in the sediment after the flow passes through the dam. This can be expressed as P=1-λ(1-R)(1-C_(da))/1-(1-R)C_(da) in which P trap efficiency, Rerate in reduction of volumetric sediment concentration, C_(da)=pre-dam passing volumetric sediment concentration in a debris flow, and C_(da)=C=_(da) debouchment ratio which is approximately 0.9. This equation states that the regularity of the mutual movement of the sediment between a debris flow and a slit dam is related to the relative width of the dam opening, slit density and the pre-dam passing volumetric sediment concentration. This study establishes a general design model on slit dam opening width by incorporating the pre-dam passing volumetric sediment concentration, trap efficiency and rate of reduction in volumetric sediment concentration in a debris flow. This model can easily derive the opening width of slit dams specific to different geological structures and dam trap efficiency. At the same time a slit dam must have the capability to convert a debris flow into a less damaging sediment-laden flow for the safety of the preserved downstream area. This study has also developed a safety design model and a nomograph which can be used as a reference in future for engineering designs.