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 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 (8290 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 area of the Jhong-jheng Bridge of the Tou-chien River as a full scale 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 “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. According to the data of cross-section survey and digital surface model in this study reach, the river migration can be divided into the following stages. (1) The initial stage of the Jhong-jheng Bridge completion (before 1986): sediment deposition occurred in this area. (2) Protection Works are built on the downstream of the Jhong-jheng Bridge in sequence (1986 to 2012): the maximum erosion depth downstream of the drop structures is up to 15 meters, and there is no significant change of riverbed elevation in the upstream of the Jhong-jheng Bridge. (3) A new channel was developed at the right-hand side of the protection works (after 2012): The Typhoon Soulik widened the new river channel, and sediments were transported from upstream to downstream. The event caused the headward erosion of rock river-bed and channel knickpoint migration. 2. Based on the results of site investigation, the erosion processes of soft rock river-bed included (1) trenching incision and plucking , which were observed from the Jhong-jheng Bridge to 200 meters upstream of the Bridge; (2) uniform incision, plucking, bedload abrasion occurred from.200 meters upstream of the Jhong-jheng Bridge to the Sin-jhong-jheng Bridge: 3. The CCHE2D computer program was applied to simulate the channel variation in this area. The preliminary calculation results show that CCHE2D can be adopted for study the bedrock erosion behavior in the area. 4. Partially grouted riprap consists of specifically sized rocks that are placed above the riverbed and grouted together with grout filling 50% or less of the total void space. In contrast to fully grouted riprap, partial grouting increases the overall stability of the riprap installation unit without sacrificing flexibility or permeability. This project plans to demonstrate the partially grouted riprap on the upstream channel of the Jhong-jheng Bridge next year, and compile a guideline for constructing partially grouted riprap on Taiwan river channel in future.