本文藉由試驗探討保護工對橋墩周圍底床沖淤變化的影響，試驗部份為兩組配置，一組為單一橋墩的情況，另一組則在橋墩前方19.5公分處設置本文探討的保護工，由蛇籠與許多橡皮環圈組成，比較試驗後橋墩周圍的沖淤情形。在單一橋墩的情況下，橋墩周圍將產生嚴重的沖刷，甚至淘刷橋樁附近的泥砂，橋墩的基樁因此裸露，將造成橋墩結構安全性的危害。當橋墩前方設置環圈堆保護工後，只有在橋墩右方底床沖刷了4公分，且在墩後有泥砂回淤的情形，保護橋墩效果相當不錯。
但是在流場方面，由於試驗水深過淺，無法以儀器去量測流速，因此以FLOW-3D數值模式模擬底床附近的流場，並用以說明不同保護工配置對於橋墩保護之可能效果。由模擬結果可以發現，當設置保護工後，正向水流被保護工分為左右兩股水流，雖然造成渠道兩側產生高流速水流，但在保護工後形成一廣大的流速緩慢區，此緩慢區涵蓋住整個橋墩周圍，達到保護橋墩的功用。
本文以試驗的兩組配置，用數值方法去做延伸模擬，如橡皮環圈的尺寸改變、蛇籠的幾何形狀變化與保護工與橋墩的相對距離不同。比較近底床的流場分佈，發現保護工有環繞橡皮環圈堆時，對橋墩保護的效果較好，而小尺寸的橡皮環圈堆比大尺寸的環圈堆有較佳的保護橋墩效果；在蛇籠幾何形狀變化上，圓形造成的流速緩慢區較大，但是在保護工周圍會產生較嚴重沖刷；在距離變化，本文模擬三種距離，以保護工距離橋墩9.75公分時，有較好的保護效果。

This study presents some sets of experimental data to understand the scour situation on near bed around the bridge pier. Because experimental water depth is very shallow, we are unable to measure the near-bed flow velocities by instruments. So, we simulate the flow velocities on the near bed by the FLOW-3D numerical model.
There are two groups of bridge pier’s experiment, one group was conducted at a single pier situation with protection work for the bridge, and another was carried out with 19.5cm bridge protection work front of the bridge pier. This protection work composes of a triangular gabion and many rings. This study compares the experimental results of the local scour depth around the bridge pier.
Experimental result of a single bridge pier without protection work shows that the bed around bridge pier was seriously scoured. Because the sediment under the bridge pier is seriously eroded and the bridge stake is exposed, so the safety of bridge stake will be endangered.
When the protection work is set up in front of the bridge pier, no significant scour near the bridge pier is found and this shows that the protection work has the good protection for the bridge.
In the part of numerical simulation, the flow field of two experimental groups is simulated by the FLOW-3D. By the simulation results, we can find a characteristic of very slow velocity range at the back of the protection. This range includes the bridge pier; the bed around the bridge pier can be protected. But it causes two high velocities in the bridge pier downstream.
In addition to simulation of two groups of experiment, we have to simulate the other groups. Rings size, shape of gabion and distance between the protection work and the bridge pier are changed.
This study analyzes the flow field on near bed of every simulated result. We know the protection work will be very good if it is encircled by many rings. Big sizes of rings are more effective than small ones. A triangular gabion is more effective than the circle one. In the part of numerical simulation for different distances, we can find more effective of distance as 9.75cm than other groups.

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