橋基裸露是目前台灣跨河橋樑設計及其安全維修所面臨最急迫問題之一。因河床之逐年下降，裸露之橋基因其迎水面寬較大，將會於橋基處引致更大之局部沖刷，使基礎淘空下陷之潛勢增高。目前針對局部橋基保護工如包墩或蛇籠護坦等，若規劃或施工不當，則可能因攔阻水流而造成河道內或相鄰橋墩間之束縮沖刷，進而使橋基保護工破損且危及橋基之安全。因此，不均勻橋墩的沖刷特性，需要進一步加以研究，以研擬出適當的橋基保護工法。 本文以理論分析及動床實驗來探討河槽內不均勻圓柱形橋墩(即圓柱形橋墩位於圓形基礎上)及群樁基礎之局部沖刷及束縮沖刷特性，及探討橋墩佈置及流況對局部沖刷之影響，以求得圓形基礎及群樁基礎之局部最大沖刷深度、最大堆積丘位置及沖刷範圍。 實驗結果發現，橋基頂端高程位置高於底床時其局部沖刷深度較均勻橋墩時大；橋基頂端高程位置介於底床和最大局部沖刷深度之間時可減少局部沖刷深度。在雙柱橋墩橫向排列時，其雙柱間距( s )越小，局部沖刷沖刷深度越大，當s = 0時會產生最大的局部刷深。 Most rivers in Taiwan are severely degrading during last two decades due to fast growing in-stream sand mining and construction of water supply or diversion works. Consequently, the exposure of bridge foundations, such as caissons and piles of bridge piers , is one of the most critical issue for the design and maintenance of river-crossing bridges. Inadequate design of countermeasures at bridge crossings may incur further local and contraction scours. The scouring process, such as maximum scour depth and scour dept and scour depth and scour range, around non-uniform piers and pile foundations are examined in this study by employing laboratory experiments . The suitable countermeasures for those foundations will is also investigated
