伶仃洋大桥东锚碇筑岛围堰冲刷试验研究

Cofferdam scouring of east anchor island of Lingdingyang Bridge experimental study

深中通道伶仃洋大桥为主跨1666 m的三跨钢箱梁悬索桥,其东锚碇为海中重力式锚碇,采用水中筑岛+地连墙支护的施工工艺,筑岛结构为“锁口钢管桩+工字型板桩+平行钢丝索”组合式围堰结构,筑岛直径150 m,由于筑岛面积较大且施工区域台风频发等特点,受海域水动力的影响局部会发生严重的冲刷和淤积,产生施工风险。通过多工况冲刷模型对比试验和有限元计算,结果表明:回填砂能够有效减小河床的冲刷,回填碎石的起动流速大于平均流速0.6 m/s下的围堰局部最大流速0.91 m/s,不易受水流力的影响;同时先施工上、下游侧,再施工顺水流两侧的施工顺序能够将大部冲刷面积限制在筑岛围堰外侧,能够有效地保障围堰内抛填质量,成岛后在外围施工20 m膜袋砂的防护结构作为抗台储备时,防护外的实际冲刷深度控制在5 m左右,围堰结构稳定、防护结构形式安全可靠。

The Lingdingyang Bridge is a three-span steel box girder suspension bridge with a main span of 1666 m on the Shenzhen-Zhongshan Link.The east anchorage is a gravity anchorage in the sea.The construction technology of island building in water and ground connecting wall is adopted.The island structure is the combined cofferdam structure of"locking steel pipe piles+I-shaped sheet piles+parallel wire ropes".The island′s diameter is 150 m.Due to the large scale of the island and the frequent occurrence of typhoons in the construction area,localized hydrodynamic forces can lead to severe erosion and siltation,causing construction risks.The comparison test and finite element results of the scouring model under multiple working conditions described in this paper show that the backfill sand effectively scours the small riverbed,and the starting velocity of the backfill gravel exceeds the local maximum velocity of 0.91 m/s of the cofferdam under the average velocity of 0.6 m/s,thus reducing its susceptibility to flow force.At the same time,a construction sequence involving initial construction of the upstream and downstream sides,followed by construction along the water flow,confines most of the scouring to the outside of the island building cofferdam,which can effectively guarantee the quality of throwing and filling in the cofferdam.After the island is formed,when the protective structure of 20 m film bag sand is constructed around the perimeter as a reserve against the typhoon,the actual scouring depth outside the protection is controlled within 5 m,the cofferdam structure is stable,and the protective structure is safe and reliable.