以渠槽試驗比較透水與不透水固床工下游之沖刷坑差異

Comparison of Downstream Erosion Between Permeable and Impermeable Groundsill Throung Flume Tests

孫崇育(Chong-Yu Sun) ； 許少華(Shaohua Marko Hsu) ； 吳俊鈜(Chun-Hung Wu) ； 洪碧芳(Pi-Fang Hung)

《中華水土保持學報》 49卷2期 (2018/06) Pp. 117-130

https://doi.org/10.29417/JCSWC.201806_49(2).0006

摘要

本研究以固床工之透水與不透水性進行固床工下游基礎點沖刷之探討。室內實驗發現不透水固床工會產生較深之基礎淘刷，而透水性固床工則較輕微。其主因乃水流流經透水性固床工時會有穿透流及溢頂流兩種流況，使跌水之流量減少，進而減少跌水（溢頂流）對底床產生之衝擊，此外，穿透流也會讓溢頂流之跌水位置往下游推。溢頂流減少之差異可以從固床工孔隙率不同得知，孔隙率0.27(K≈1.25 cm/s)的溢頂流減少7 %、孔隙率0.34(K≈1.25 cm/s)的溢頂流減少20 %，得知透水性固床工之孔隙率愈大，減少溢頂流愈大，其溢頂流之流量會愈小，而穿透流之流量會愈大，使之基礎點沖刷深度漸緩。

關鍵字

流況 ； 固床工 ； 渠槽試驗 ； 透水性 ； 基礎點沖刷 ； 穿透流 ； 溢頂流 ； 孔隙率

並列摘要

This study compared downstream scouring between permeable and impermeable groundsill. Site investigations were first performed at the Dajia River Bridge and a flume experiment with a scale of 1 to 100 was designed based on field data. The discussion focuses on the differences between permeable and impermeable groundsill. Field investigation showed that severe localized scouring occurs downstream of a impermeable groundsill, whereas deposition occurs downstream of a permeable groundsill. Laboratory experiments showed that for an impermeable groundsill, scouring is much deeper than for a permeable groundsill. The main cause is that a portion of flow penetrates the permeable groundsill and reduces the over-weir flow over the groundsill, thereby reducing the impact on the surface bed. Furthermore, increased penetrated volume allows for some of the vertical flow to flow laterally downstream because of a decrease in water height. The reduction in over-weir flow is correlated with porosity. A porosity of 0.27 (K≈1.25 cm/s) reduces the flow by 7%, and a porosity of 0.34 (K≈1.25 cm/s) reduces the flow by 20%. Greater porosity cause greater reduction in over-weir flow, the impact on the surface bed.

並列關鍵字

flow pattern ； groundsill ； flume experiment ； permeability ； scouring at base point ； penetrating flow ； over-weir flow ； porosity