圖書典藏及影音數位平台

中正大橋河段現況呈現大範圍軟弱岩質河床裸露現象並持續擴大範圍，軟弱岩質河床沖蝕特性與沖積型河床並不相同，本署水利規劃試驗所近年曾辦理軟岩質河床沖蝕行為研究並建立河道模擬評估工具，其相關成果可應用於本河段進行河道動床模擬，並針對中正大橋改建後河段沖淤影響及變遷趨勢進行評估。 對於河道地形快速下切變動之河段，常用穩定工法包含利用固床工、表層灌漿、鼎塊堆置等方式進行軟弱岩質河床之沖蝕保護，但成效常受到軟岩沖蝕作用之影響而不如預期。部份固結灌漿工法於國外文獻已有多年之應用，但於國內則尚無實際應用案例，其工法特性與施作要點可加以研究，評估應用於穩定本河段軟弱岩質河床之沖蝕作用。

Continuous river channel migration at the area of the Jhong-jheng Bridge of the Tou-chien River by rapid bedrock erosion could be a great threat to the function and the safety of cross-river infrastructures. According to the historical hydrological data, the typhoon SOULIK in 2013 was the most significant hydrologic event in the period from 1991 to 2015. This event resulted in a peak discharge close to 100-year return-period discharge Q100 (8,190 cms). This event destroyed the 9th pier of the Jhong-jheng Bridge and widened the river channel at right side of the abutment. Therefore, proper countermeasures at this area to prevent rapid bedrock erosion are needed. Taking the channel area at the Jhong-jheng Bridge, the Tou-chien River as a full scale physical model, this two-year project aims to accomplish the following four objects: (1) to understand the processes and phenomena of the channel migration; (2) to determine the river channel variation under long term and short term conditions by the mobile-bed numerical simulation; (3) to demonstrate the efficiency of “partially grouted riprap” method for stabilizing rock riverbed eroded channel; (4) to recommend the countermeasures at the area of the Jhong-jheng Bridge of the Tou-chien River. The following conclusions can be drawn based on the tasks accomplished in this year. 1. The partially grouted riprap (PGR) test result shows a significant effect to against bedrock erosion. Only 20% of the area is complete damage, nevertheless 80% of the riverbed below PGR is not eroded. This project compile a guideline for constructing partially grouted riprap on Taiwan river channel. We recommend to develop a local improvement methods and analysis methods in the future. 2. The countermeasures at the area of the Jhong-jheng Bridge of the Tou-chien River is as follows. (1) Zero program: The channel on the right side of ground sill has widening and incision potential. Long-term simulation results show that the distance from the right river bank and the new bridge pier is about 91 m. Hence, no major countermeasure is recommended with the local erosion mitigation strategy and observed regularly. (2) Stable slope countermeasure: We consider the river bed slope 1/160 on 1978 as the reference slope, and adjustment the elevation on section of the Jhong-jheng Bridge to 56 m by permeable or continuous ground sill. After adjustment, the slope of upstream reaches is close to 1/160, and the downstream slope keeps 1/200. PGR method is recommended for protecting the foundation of ground sill. (3) Local erosion mitigation countermeasure: In this project, we suggest to use PGR and river channel arrangement to against the knickpoint retreat. It is recommended to adjust the flow direction keep away from the Ma-yuan-du embankment, and partial reinforcement the foundation near the river bank.