台灣近年來由於公共建設的蓬勃發展及盜採砂石問題日益嚴重，促使天然河道中之輸砂更為不平衡，造成底床逐年下降，橋基裸露將對橋樑結構安全性產生重大影響橋。然而目前針對局部橋基保護工法若施工或規劃不當，可能由於束縮沖刷或者水中夾雜著浮木巨石而導致反效果。因此需對不同形式之橋墩基礎的沖刷特性加以研究，以發展出適當之橋基保護工法。 本研究利用動床水槽試驗分析橋墩周圍施以套環保護工法及不均勻橋墩之局部沖刷特性，分析其最大沖刷深度變化、發生位置、沖刷坑及堆積丘範圍，並比較在不同裸露高度下之沖刷變化。 實驗結果發現，套環保護工設置位置越靠近底床時，刷深越小；當貼齊底床時，可明顯減少最大沖刷深度，並成功的將向下射流與馬蹄形渦流導向墩後遠離主要橋墩基礎結構。當套環厚度增加時，沖刷坑範圍與刷深增加並不明顯，故造成沖刷的主因為馬蹄形渦流，向下射流的影響有限。不均勻橋墩在不同橋基位置時，隨著裸露高度增加而造成迎水面積增加，沖刷坑範圍及最大刷深增加；當橋基貼齊底床而墩前無沖刷發生時，與套環保護工結果相似；而當墩前橋基裸露時，則刷深較套環保護工大。 This study uses experimental mobile channel to examine the characteristics of local scour around non-uniform piers and the piers with collar protection. The maximum scour depth and the range of the scour hole is analyzed. Furthermore, the change of scour at different exposure elevations is compared by performing a series of case studies. When the collar is close to the bed, the scour depth decreases. When it’s top is flush with the bed, the scour depth decreases obviously, and both the downflow and horseshoe vortex are guided to the downstream successfully far away from the bridge pier structure. The scour depth doesn’t change obviously with the increase of the location of the collar, so the horseshoe vortex is the main factor for scouring. The experiments of non-uniform piers at different exposure elevations showed that the increase of exposure elevation causes the increase of obstruction area. So, the range of scour hole and the depth of scour will increase. When the top of the pier foundation is flush with the bed, the scour doesn’t occur in front of the pier foundation, the result is similar to that for using collar. While the scour depth is much deeper for those causes when the scour occurs in front of the pier.
