A Study On Failure Analysis And Repairing Method For Deepwater Mound Breakwaters

The main function of breakwater is to defend sea area to be covered against effect ofopen sea waves. Broadly, any marine structure which is used to defend against wave, flow,sand and floating ice into the protected area, can be considered as a breakwater. It plays animportant role and has a special position in coastal engineering. Nowadays, as the gradualoutward shift of port site, it is becoming more and more common that breakwaters areconstructed at the sea deeper than20meters."Code of Design and Construction ofBreakwaters (JTS154-1-2011)" has defined that breakwaters at a depth of more than20meters are deepwater breakwaters, whose cross-section type, dimension and constructionrequirements, etc. are different from general ones. Especially when destroyed, it canfrequently cause serious economic losses and great influence.With the background of the damage of the breakwater in one shipyard, this thesis collectsand analyzes the phenomenon and reason of11breakwater damages at home and abroad,especially focuses on destruction examples of deepwater breakwater projects, analyzes thecause and proposes restoration scheme of this breakwater, and optimizes it combining theresult of physical model experiments. The conclusions are as follows：(1)By analyzing10breakwater damages at home and abroad, the reasons for thedestruction of breakwaters include: inaccurate wave data, existing calculate method which cannot consider all elements, such as breaking waves, oblique waves, etc., structure designproblems, such as overtopping scouring, structure instability, insufficient foundation bearingcapacity, fracture of armor blocks, structural defects, etc., and construction quality controllingdefects.(2)By analyzing the breakwater destruction above mentioned, we summarize the reasons for the destruction including: first, calculated wave was much smaller than actual, so smallerarmor blocks were designed and destroyed during Typhoon; second, the elevation of lowerstone prism was too high, and the armor blocks slid after the instability of stone, therefore thesurface was destroyed in large area; third, there was no bottom rock in original design, whichmight be one reason for the destruction; only one row of armor blocks were designed on thebreakwater shoulder, which easily caused removal of stones in the front and bottom of thewave walls; during construction of the wave wall the bad combination of different layers ofconcrete caused destruction of the wave walls. In view of the possible reasons abovementioned, we propose a structure of mound breakwater with shoulder armored by accropodeblocks as restoration.(3) Proved by physical model experiment, the cross-section of the breakwater isoptimized as follows: raising the height of the shoulder up to1.3m to make waves brokenahead of breakwater in order to reduce overtopping; lowering the elevation of bottomprotection to-11.5m to reduce the shock effect by the wave and flow along the breakwater;under the elevation one time of wave height below the water level, reducing the weight ofblocks appropriately because of less force received. According to the feature of the project,after overtopping influence analysis, control the elevation of wave wall appropriately withoutinfluence over working of fitting-out berth.