The bridge pier and river embankment protection
Flow vortexes are generated at the surrounding area of a bridge pier when water passes through it. This phenomenon could cause severe erosion at the bottom of a pier and therefore, it is a threat to stability of the pier, especially during flood events. This research’s aim is to develop a soft device that could effectively eliminate or reduce the vortex phenomenon, and then slow down the bed erosion, so as to protect bridge pier.
The bridge pier and river embankment protection P4 P5 National Cheng Kung University , Taiwan Ta-Hsiung Peng Ph. D. Candidate 2010/08/30 1 Content INTRODUCTION RESEARCH METHODOLOGY RESULTS AND DISCUSSIONS CONCLUSIONS 2 INTRODUCTION Flow vortexes are generated at the surrounding area of a bridge pier when water passes through it. This phenomenon could cause severe erosion at the bottom of a pier and therefore, it is a threat to stability of the pier, especially during flood events. This researchâ€™s aim is to develop a soft device that could effectively eliminate or reduce the vortex phenomenon, and then slow down the bed erosion, so as to protect bridge pier. 3 INTRODUCTION The field investigation of present research was conducted at the prier #5 of Tsengwen-River Bridge No. 2. The soft device was constructed by used tires of vehicles, attached with soft metal blades/fins on its surface. This device is also named as â€˜a stack of rings with soft bladesâ€™. The soft devices were set up around the bride pier. 4 INTRODUCTION The flow patterns around the bridge pier during flood events were observed, and the variations of river bed around the pier were also observed to check the effectiveness of the soft device. The results showed that the soft device could effectively reduce the vortex intensity around piers, so as to reduce erosion ability and the sediments deposited around the bridge pier. The proposed device has proved that it has the capability of protecting bridge pier against scouring. And the device also passed the serious test of the huge flood (8,400CMS) of Morakot typhoon in the 2009. 5 INTRODUCTION Flow vortexes are also generated when the flood touched the wall of river bank. Once, if the sediment released, it can not recovered. Thus scoured would be happened at the foundation of the embankment. The bottom of the foundation become empty and finally the structure will be collapsed. The devices set up in the concave bank of the river. The energy is reduced and the sediment will be deposited. It can protect the river embankment. 6 RESEARCH METHODOLOGY Vortex happened surround the bridge pier(Ettema,1980) 7 RESEARCH METHODOLOGY Existing pier scour prevention technology and its characteristics can be divided into three types: To strengthen anti-erosion ability of local piers. To reduce water impact. To increase the amount of the sediment of bridge pier. 8 RESEARCH METHODOLOGY â€˘ First method, i.e. rock, tetrapod, gabion, concrete block, in particular gabion is one of the most popular devices. One disadvantage of this method is that it can not joint with riverbed, and interfere with the flow field, hence its structure is not stable and failed in protection. 9 RESEARCH METHODOLOGY â€˘ Second method- rings set up around piers, blocking water flow and reducing horseshoe vortex as well as erosion. If the piles were installed in front of piers, the sheltering effect thereby will reduce erosion. 10 RESEARCH METHODOLOGY â€˘ Third method- increase the amount of sediment surround local piers, i.e. sediment transported by diverse way moves to scour areas, and then add the deposited sediment. 11 RESEARCH METHODOLOGY • Hence, the protection method named as “a stack of rings with soft blade“ has been developed by combining the three above mentioned methods. For the first method, to strengthen anti-erosion ability of local piers was used. Sheltering and slow water flow was employed from the second one. From the third one, sediment diversion supplementary method was used to add sand to the exposed places and to reduce scour. 12 Laboratory experiment Exposed pile pier After the flood fill up pile with sediment 13 Use of heavy solid protection structure such as tetrapod, rock e.t.c. Before flood event 2003, The pier P4&P5 of Tsengwen-river bridge 2003/06/11 Left side P 5 Main groove P 4 P 5 right side 2008/12/07 After flood event 2003, the solid tetrapod, rock washed away at the same pier no. P4 and P5 P 6 Main groove 14 Protection device setup P 5 ĺˇŚ ĺ ´ A rectangular wire gabion filled with stone at the rear of bridge pier. The front triangle wire gabion fixed to ground wire gabion. The triangular wire gabion filled with stone at the front pier of P5 15 A stack of rings with soft blades bound to triangle wire gabion. Tire with soft blade 16 Set up protecting device Fixed a stack of rings with soft blade to a rectangular wire gabion in the rear bridge pier Add a stack of rings with soft blade to triangle wire gabion in the front bridge pier. P5 Completely assembled 17 Test of Sinlaku typhoon â€˘ There were four bridges broken in Taiwan in this typhoon (2008/9/14). â€˘ Flood almost covered to the bottom of the bridge. 18 Broken bridge in Sinlaku typhoon Ho-Fong bridge in Taichung county Jiasian bridge in Kaohsiung county Wufuliau bridge in Chiayi county Liau-Ming bridge in Buli town 19 Bridge pier submerged in flood (Sep. 14, 2008) P6 20 Protecting device in flood(Sep. 16, 2008) P 5 P 5 in Ma ove gro n ai e M oov gr （ photo from the front side ） P 5 （ photo from the left of front side ） M gr ain oo ve （ photo from the right of front side ） 21 P 5 P 5 The shielding effect in front triangle gabion (top view) The water level of right hand side is higher than that of left hand side 50cm (energy reduced ) P 5 P 5 Main groove Main groove The turbulence of outside of pier P5 22 Protecting device in flood of Sinlaku typhoon(retrieval period) 23 After Sinlaku typhoon and Jangmi typhoon later Ground wire gabion ďźˆ photo from right side ďź‰ Sediment deposited between the bridge pier 80 cm of sediment had been already deposited between the protecting device and bridge pier The outlook of triangle 24 After Sinlaku typhoon and Jangmi typhoon later The protecting device before the front pier(top view) The protecting device after the rear pier(top view) 25 Comparison of sediment deposited between the surround of P5(with device) and that of P4(without device) P 5 Main groove Main groove P5(Dec. 9, 2008) Right side of P5 Ma in g ro ov e Sediment deposited surround of P5(with Surround of P5 and P4 Left side of P4 Main gro ov e 26 Foundation was eroded in pier P4(without device) Comparison of sediment deposited between the surround of P5(with device) and that of P4(without device) 27 Test of Morakot typhoon • It happened from 2009/8/7 to 2009/8/10 ， the accumulated rainfall which is the largest rainfall of Ali stations located on the upstream of Tseng Wen Reservoir, up to 3004.5mm has exceeded the average annual rainfall of 2500mm of Taiwan. • It started to discharge from Tseng Wen Reservoir, it arrive 8,400cms quantity from 2009/8/8 to 200/8/11. 28 Protecting device in flood of Morakot typhoon(retrieval period) 29 Flood flow through the bridge Aug. 9, 2009 Top view of the triangle wire gabion (Aug. 13, 2009) Flood flow through the pier P5 (Aug. 13, 2009) Energy reduction by the flexibility of both sides of the tire (Aug. 13, 2009) 30 The condition after Morakot typhoon 31 ă€Œ The stack rings with soft blade ă€? protecting device has the following characteristics 1. The direction of flow is changed and reduced flow speed 2. Destruction is not easy 3. It will not sink because install ground wire gabion under device in future time. 4. The existing structure is not destroyed 5. The protection of workers is easy to replace 6. The cost of protecting workers is lower 32 Conclusion • 「 The stack rings with soft blade 」 in the protecting device, setup with different directions and inclined angle, and flexible blade can increase the friction coefficient, and then to reduce the power of the flood and erosion and then protect the foundation of the pier. When the flood flow encounters inside the tire, it will cause the circulation motion inside the tire, which can also offset the energy of flood. The flexibility of the tire is used to prevent from the hitting objects such as stone, log and large floating objects 。 33 Conclusion • Comparison of P4, P5 and P6 sediment deposited around the pier, it is clear that P5 pier installed by 「 The stack rings with soft blade 」 protecting device can make sediment be deposited to protect the bridge pier foundation. 34 Protect the river embankment Flow vortexes are also generated when the flood touched the wall of river bank. Once, if the sediment released, it can not recovered. Thus scoured would be happened at the foundation of the embankment. The bottom of the foundation would become empty and finally the structure would be collapsed. The drawing shows the devices set up in the concave bank of the river. The energy would be reduced and the sediment would be deposited. It would protect the river embankment. The drawing shows the design of the device. 35 Thanks for your attention 36