Application of Ring Consolidation Works to Bridge Pier Protection

Abstract

Recently, the extreme climate types occur frequently under the effect of climate change. In addition, the annual rainfall concentrates in the summer in Taiwan. Bed elevations of many rivers in western Taiwan lower down seriously, due to unbalanced sediment transport. It causes the scouring of the river bed around the pier, and results in the exposure of the pier foundation and impacts the safety of bridge.

The result shows that the consolidation works sets in downstream of the pier can uplift the water depth and decrease the energy of flow impacting bridge. The different configurations of consolidation works can reduce the maximum scour depth in front of the pier. When the sawtooth-type ring consolidation worksets at a distance of 1 time to the pier diameter, a height of half time to the pier diameter, a width of saw tooth of 0.8 time to the pier diameter, it is the optimal type among the experimental conditions conducted in this study. The optimal allocation (L/b=1, h/b=0.5, W/b=0.8) can reduce 57.3% of the pier scour depth reduction rate and 49.4% of scour hole volume reduction rate in downsteam of consolidation works. According to experimental data, we can obtain an empirical formula by using multiple regression. The R-squared value of function is 0.877. The maximum scour depth in front of pier can be predicted by this formula.

台灣近年來因氣候急速變遷，加上降雨集中於夏季，造成豐枯期流量懸殊，其中西部河川多屬下降型河川，泥砂推移力強，河床劇烈變動，在輸砂極為不平衡情況下，橋墩沖刷加劇，經常造成橋墩因沖刷下切裸露而崩壞。因此，本研究基於橋墩安全，研發新型固床工-透水性環圈式固床工，透過改變固床工種類、設置高度、設置距離等不同配置模式進行比較分析，期能獲致較理想之固床工型式，以供相關單位工程設計之參考。

研究結果顯示，當設置固床工於橋墩下游處時，因固床工橫截水流抬升水位，降低流速使水流沖擊橋墩能量減弱，且能抑制橋墩周圍沖刷坑發展，進而減低向下射流造成橋墩墩前沖刷深度。綜合考量橋墩與固床工之安全性，本研究較佳配置型式為鋸齒式環圈固床工(L/b=1, h/b=0.5, W/b=0.8)，能有效抑制橋墩周圍沖刷坑發展，其橋墩沖刷減緩率約57.3%，固床工下游沖刷坑體積減緩率約49.4%。此外，依試驗數據，利用複迴歸方法獲致經驗公式，並經驗證得判定係數R2=0.877，透過該公式可預測出橋墩墩前最大沖刷深度。