圖書典藏及影音數位平台

現況防洪構造物歷經多年風吹日曬、颱風豪雨後，已有略成堤頂下陷、淘空滲砂與材料劣化等現象發生，對於現況防洪構造物的安全性影響極大。尤其106年尼莎?海棠颱風後沖刷影響之後，造成堤防嚴重受損亟需評估其安全性。然而整河段拆除重建工程經費龐大，為能尋求有效維修與補強方案，擬僅先就急要之河段(宜蘭河七張橋以上)委外辦理安全性評估分析及研擬改善方案。

AbstractThe Yilan River is the largest tributary at the north bank of Lanyang River. The scope of basin covers the Jiaosi Township, Yuanshan Township, Yilan City, and Jhuangwei Township etc. The tributaries of Shaochau River, Dachau River, Wushi River and Dahu River converge into it. The levees built along the river are very old. The hydraulic structures along the river are also old levees and revetments. In recent years, considering the potential risk of climate change, extreme rainfall incident, flow route change and earthquake incident, in order to seek the effective maintenance and reinforcement alternatives. It is proposed to review the safety for the bank of Yilan River through the safety investigation plan, to facilitate the subsequent maintenance and management.1. Project Cause and Work Items The scope of work of this project includes the hydraulic structures up Chichang Bridge of Yilan River. The total length of levees and revetments is about 41,492m. The work items are mainly 6 times of visual inspection of levee, including 1 time of regular inspection and 5 times of irregular inspection. 1 time of regular inspection has already been finished. The irregular inspection has not been started so far; The visual inspection, DER&U assessment have been finished for No. 2 Yungjin Bidge; As for non-destructive inspection, the ground penetrating radar was adopted to detect the levee in 43,000m of length; The strength investigation of levee structure, adopting at least 12 sets of drilling core sample to conduct the strength test and rebound hammer test for verification and comparison; The test results are integrated to carry on safety assessment of current levees, and draft the improvement countermeasures in accordance with the assessment results.2. Basic Data Investigation for Scope of ProjectThe Yilan River is the largest tributary at the north bank of Lanyang River, including the tributaries of Wushi River, Dachau River, Shaochau River, Dahu River and downstream of Yilan River. It is derived from the Sanshi Mountain (EL.1,147m) of Wushi River. The tributaries of Dahu River, Dachau River, Shaochau River are converged successively. It flows around the north part of Yilan City to Jhuangwei Township and merges to Lanyang River. The area of basin is about 149 km2. It is about half for the level land and mountain region. The basin covers the Jiaosi Township, Yuanshan Township, Yilan City, and Jhuangwei Township etc. The terrain is steep at the upstream mountain area. The tributaries of Wushi River, Dachau River and Shaochau River are short with rush flow. The slope becomes slow after entering the Lanyang plain. The steep river changes into the sinuous river and merges into Yilan River. The length of main stream at downstream is about from 14.7 km (estuary to Yuanshan Bridge). The average slope lowers about 1/2,200. The Yilan River lies in the Lanyang plain at the northeast part of Taiwan. It is the largest tributary at the north bank of Lanyang River. It lies in the subtropical climate region. In the autumn, winter of every year, it is shrouded by the continental cold air mass During the Northeastern monsoon, the maritime airstream from Pacific Ocean can drive straight in, meet the high mountain barrier, then form a large amount of rainfall. So, this basin often has cloud and mist that curl up. The rainfall is plentiful too in autumn, winter, and often presents the drizzle continuity. The temperature is low and the humidity is high; In summer, it is often attacked by the typhoon with torrential rain. Because the mountain area is high and precipitous, causing the rivers steep with rapid flow, often lead to the water rushed down the mountain, destroy the farm field and houses. According to the meteorological statistics from 1991 to 2017 of Yilan Weather Station of Central Weather Bureau. The annual average rainfall is about 2,772.1 mm. There is more rainfall in October to November, accounts for 50% of the total rainfall in the whole year; The average monthly rainfall is between 130~432 mm.3. Visual Inspection Result of LeveeThe regular inspection of this project was handled from May 3 to 4 of 2018. The scope of inspection included levees at both banks of Yilan River Yilan (upstream of Chichang Bridge), Shaochau River, Dachau River, Wushi River and Dahu River. There are 39 levees, and the total length is 41,492m.In this regular inspection, there were 19 damaged places, in which 9 for Yilan River, 4 for Dachau River, 3 for Shaochau River, 3 for Wushi River and 1 for Dahu River. All of these 19 damaged places should be planned for improvement in accordance with the scale and current condition. It is still unlikely to cause endangering to damage the levee body structure immediately. The damage type is mainly the crack per further statistic of classification regularly, in which 13 places account for 68%. Other damage includes the hole, washing empty, stripping and destruction etc., and only take 1~2 places specifically; Most levee body damage is occurred at top of levee having 11 places. 2~4 places are in front of the levee slope, footing and rear slope of levee. The reason for wide distribution at top of levee might be the adoption of RC pavement. The RC pavement is flexible pavement. So, if the soil in levee body is sinking or slipping slightly, it can cause the cracking or misplacing of pavement.4. Inspection Result of Non-destructive InspectionIn this project, the ground penetrating radar was adopted to detect 27 places at Maichou Levee, Yungho Levee, Jhuangwei Levee, Jeylong Levee, and No. 1 Alancheng Levee etc. As for the test line planning, various test operations are carried out according to initial working conference and resolution of project. The detection length of ground penetrating radar was 43,244m. The ratio of slightly cavity signal is not high, which is below about 1%. It reveals the inner state of levee body is still good. Only two levee sections must be paid special attention. There is intermediate cavity signal at 0K+492~0K+495 of Dachau River Tsejehlon Levee. It is proposed to handle the repairing action. There is 10m slightly cavity signal at 0K+279~0K+289 of Dachau River No. 1 Alancheng Levee, it must be paid special attention, and observe whether the hole expands.5. Investigation Results for Strength of Hydraulic StructuresIn this project, the drilling core test is planned for 12 places of Fudeh Levee, Paolung Levee, Jeylong Levee, No. 1 Erjay Levee, No. 3 Erjay Levee, Tsejehlon Levee (2 places), Jenshan Levee, No. 2 Jenshan Levee, No. 1 Ejay Levee, Gangtsajeh Levee, Lichebay Levee etc. As for the planning of drilling core position, 3 sets of drilling core test are planned for every place. the compression strength of drilling core samples lies between 172 kgf/cm2~465 kgf/cm2, and the average strength of 3 samples lies between 229 kgf/cm2~452kgf/cm2. The acceptance standard of drilling core sample is 0.85 times of design strength. As for 175 kgf /cm2 of levee design strength, the compression strength of drilling core samples should be above 148 kgf /cm2. It reveals that the degradation state within the levee body is not severe at present.Additionally, the rebound hammer test is adopted to verify the results in auxiliary. From the results, it is known that the results of rebound hammer test have been underestimated. The reason is that there should be good positive correlation for the concrete under good state for conversion chart in the laboratory. The field surface of levee is undergone long-term physical and chemical weathering and sunshine etc., which cause the surface to have the situation of brittle, so the rebound hammer test situation is on the low side, therefore the convert compression strength of rebound hammer test is underestimated.6. Current Condition Assessment Results of LeveeThe safety assessment results of levee include 5 items: (1) results of visual inspection and non-destructive inspection; (2) historical data of river embankment; (3) security subject behind the levee; (4) assessment of levee body structure; (5) assessment of environmental factor. The total assessment score is 100 points. The assessment results are divided into two categories, one is damaged and the other one in not damaged. If the levee section is damaged, the assessment grade will be normal, planned for improvement, noticed for improvement, ready for improvement; If the levee section is not damaged, the assessment grade will be normal, strengthen inspection, main inspection, review inspection for levee safety.According to the flood-prevention project record tables and real existing length of every levee, about 300m is adopted to divide the assessment sections. So the scope of this project can be divided into 129 sets of levee sections and according to the index mark of every assessment to assess the improvement level of every levee section. According to the summation of every existing assessment index, and only consider the inspection requirement in flood season, there are 59 sets of assessment section belong to normal section, 2 sets should be noticed for improvement, 12 sets should be planned for improvement and 56 sets should be paid more attention.Keywords: Yilan River, hydraulic structure, non-destructive inspection, structure safety test