中国南海岛礁护岸防波堤在波浪冲击作用下稳定性试验研究

Experimental Study on Stability of Revetment Breakwater Built on Reclaimed Coral Reef Islands in South China Sea under Extreme Wave Impact

南海对我国经济发展、资源开发与运输、维护国土完整具有战略性意义,目前我国已在南海海域以吹填方式建设了一系列的岛礁。为维护这些吹填岛礁的整体稳定性,在吹填体外围边缘修建了大量护岸防波堤,以避免海洋波浪的强力冲刷。岛礁护岸防波堤在极端风浪作用下的安全稳定性,是保证岛礁吹填体整体稳定的前提。以我国南海岛礁吹填工程为背景,采用大型物理水槽模型试验方法,研究南海岛礁护岸防波堤在设防极端风浪作用下的稳定性。研究表明:在设防极端风浪作用下,南海护岸防波堤的波浪冲击力可以达到50 kPa;防波堤的水平位移和沉降较小,地基发生较大位移变形的可能性低;钙质砂吹填土地基内由于土体的塑性体应变与越浪量造成了一定的孔隙压力累积上升,但并没有出现液化现象,稳定性基本能够得到保障;在设防的极端风浪作用下,现有的护岸防波堤设计可能造成越浪量过大,在没有扭王块消浪的情况下,海水越浪量可达到每延米195 m^3/h,会造成岛礁植被死亡,地下淡化水体被海水污染,延缓淡化水体的形成过程;采取放置扭王块措施可以有效减少海水越浪量,但也可以达到每延米56.3 m^3/h。南海岛礁护岸防波堤的防浪高度和防越浪能力需要引起关注。

The South China Sea has strategic significance for China′s economic development,resource exploitation and transportation,as well as safeguarding the integrity of territory.Currently,a series of coral reef islands have been successfully constructed in the way of reclamation in the South China Sea by China.In order to maintain the stability of these reclaimed coral reef islands,a large number of revetment breakwaters have been built along the margin of these reclaimed islands,to avoid the strong scouring applied by ocean wave.Therefore,the stability of these revetment breakwaters under the impact by extreme ocean waves is the precondition for the stability of these reclaimed coral reef islands.In this study,taking the reclamation project of coral reef islands in the South China Sea as the engineering background,three large-scale physical modelling wave flumes tests are conducted to investigate the stability of the revetment breakwaters built on these reclaimed coral reef islands under the fortified ocean wave impact.The experimental results of wave flume tests show that the peak impact force on the caisson applied by fortified ocean wave could reach up to 50 kPa.The wave-induced horizontal displacement and subsidence of the revetment breakwaters is minor;and it is impossible for the calcareous foundation of the revetment breakwater to generate large deformation.It is find that residual pore pressure builds up in the reclaimed calcareous foundation of revetment breakwaters due to the irreversible plastic volumetric strain and overtopping of seawater under wave impact.However,liquefaction does not occur in the reclaimed calcareous foundation.As a result,it could concluded that the stability of the revetment breakwaters built on these reclaimed coral reef islands in South China Sea is quite well under the fortified ocean wave impact.However,the water volume due to wave overtopping is excessive.The water volume of overtopping could reach up to 195 m^3/h per meter in length if there is no accropode used to dissipate wave energy;meanwhile it is only about 56.3 m^3/h per meter in length if there are accropodes are placed in the front of revetment breakwater.It is indicated that accropodes indeed are effective to dissipate wave energy in the engineering practice.Excessive seawater overtopping from the revetment breakwater certainly will cause the death of vegetation,and contaminate the underground desalinated water on these reclaimed coral reef islands.It is highly suggested to pay our attention on the ability of the revetment breakwaters on these reclaimed coral reef islands in South China Sea to resist overtopping of wave.