不同乾砌石工淤砂作用之研究

Study on Deposition Effect of Different Dry Masonry Work

王俊傑(Jyun-Jie Wang)

指導教授 ： 張德鑫

中原大學/工學院/土木工程研究所/碩士(2012年)

https://doi.org/10.6840/cycu201200528

摘要

近年來國內積極推動近自然工法，但在近自然工法之設計上常引用國外相關設計案例，或僅根據設計者經驗為主，較缺乏水理或力學分析之基礎，因此設計上仍存在諸多不確定性。國外文獻及國內實際案例中，部份河川堤岸保護工程中常採用「乾砌石工法」，此方法確實能達到降低流速及減緩水流對堤岸沖刷之效果，但各塊石間縫隙所填塞砂石，其填塞量與粒徑大小、分佈等，常影響到乾 砌石之穩定性。
為探討不同砌石工法之水理現象，本研究利用水工模型試驗，探討逆魚鱗、順魚鱗及垂直魚鱗等三種不同之乾砌法其水力淤砂效果，模擬在工程完成及通水後，於初期、中期及達動態穩定平衡等不同階段，其斷面平均流速、砌面接近流速等水理參數之變化，據以探討曼寧係數值隨時間之改變。最後於達動態穩定平衡後，分段將砌石內所填塞之砂石取出，並分析各斷面之砂石填塞量及其粒徑分佈等，做為後續相關設計及水理演算之參考。
水工模型試驗結果顯示，通水並開始加砂後，三種乾砌法其斷面平均流速均緩慢增加（水深逐漸下降），且以砌石工表面之流速增加幅度最大，主要為砌石縫隙因淤砂填塞趨於平整，使得粗糙係數降低所致。在淤砂總量方面，粗顆粒砂填入量在砌石之前段較多，後段較少，其比例差異在10%以上，反之細顆粒砂填入量前段較少，後段較高。由試驗結果可知，粗顆粒砂石在前段先行堆積填塞，使得細顆粒砂石往下游填塞，造成前後段淤積砂之粒徑分佈有差異。

關鍵字

曼寧係數 ； 渠槽試驗 ； 乾砌石工法

並列摘要

In recent years, procedures involving nature-working methods were widely used in Taiwan. However, their designs most frequently drew directly on cases that took place overseas or were based on the designers’ previous experiences. Such designs lack hydraulic and dynamic mechanical analysis. The designs, therefore, can be full of uncertainties. According to studies conducted overseas and domestic engineering cases, embankment construction structures that are filled with rocks in accordance with dry masonry work can help reduce the velocity of the rivers and alleviate scour to the riverbanks. However, the amount and size of the rocks and their distribution will also have an impact on the stability of the rock-filled dam.
To examine the hydraulic phenomenon in different masonry structures, this research adopts hydraulic model test as the study method to discuss the sediment accumulation in three dry masonry structures -- inverse-scale structure, positive-scale structure and vertical-scale structure. The research simulates the early-stage, middle-stage and the stage when the sediment accumulation reaches dynamical stable balance after the construction, to study the index variations including mean flow velocity and approach velocity of stone surfacing and examine the change in Manning coefficient. Finally, when the sediment accumulation reaches dynamical stable balance, take out the rocks filled in the dam in separate sections and analyze the filling capacity, sizes of rocks and distribution in each section for future references.
The results of the hydraulic model test show that when more rocks are added, the mean flow velocity in all three masonry structures slowly increases (water depth gradually decreases). In addition, the range of velocity change is the largest near the surface where dry masonry work was applied to. It is because the gaps in the dry masonry structure are gradually filled with rock deposits and the Manning coefficient therefore lowers. In terms of the total amount of sediment, in all three masonry structures, higher amounts of larger rocks deposit in the front section and the amounts decrease by more than 10 percent in the latter section. However, smaller amounts of finer rocks are seen in the front section, compared with the latter one. The results show that larger rocks accumulate in the front section and allow smaller ones deposit in the lower reaches; the phenomenon leads to apparent discrepancy in sediment distribution in upper and lower reaches.

並列關鍵字

Channel test ； Manning coefficient ； Dry masonry working method

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