伶仃洋大桥西锚碇筑岛施工柔性围堰结构稳定性研究

深中通道伶仃洋大桥为主跨1666 m的双塔钢箱梁悬索桥,西锚碇采用“∞”字形地下连续墙+内衬围护结构,锚碇采用柔性土工管袋围堰筑岛施工。为确保围堰稳定性,根据实际海床标高,采用MIDAS GTS与OptumG2软件建立人工岛三维模型,采用有限元强度折减法,分别对长期和短期条件下7个典型截面(S1~S7)的围堰稳定性进行分析。稳定性分析结果表明:各截面均满足短期稳定安全系数大于1.10,长期稳定安全系数大于1.30的要求;短期不排水条件下为最不利工况。根据稳定性分析结果,施工中将吹填局部堆载位置调整至安全系数较大的S3截面处。为判断岛体稳定状态,筑岛过程中进行了沉降量和深层水平位移监测。位移监测结果表明:S3截面的水平位移速度发展较快,S5~S7截面位置水平位移仅次于S3截面,其他位置水平位移显著低于该4点,表明施工工艺的调整有效保证了围堰吹填过程的稳定性。

Study of Structural Stability of Flexible Cofferdam Used to Build Artificial Island to Facilitate Construction of West Anchorage of Lingdingyang Bridge

The Lingdingyang Bridge of Shenzhen-Zhongshan Link is a two-tower steel box girder suspension bridge with a main span of 1666 m.The west anchorage is supported on the foundation formed of∞-shaped diaphragm walls and inner shoring structures.For the ease of construction,an artificial island(cofferdam)is reclaimed from the sea using geotubes.3D models of the artificial island were established by MIDAS GTS and OptumG2 in accordance with the actual seabed elevation.The stability of seven typical cross-sections(S1-S7)cut from the cofferdam was analyzed by using the finite element strength reduction method in both long-term and short-term scenarios.The results show that all the seven cross-sections can meet the stability requirements,with the short-term safety factor over 1.10 and the long-term safety factor over 1.30,and the short-term scenarios dictate the design(undrained).As per stability analysis results,the reclaiming operation inducing localized overload was relocated to the cross-section S3 where larger safety factor has been achieved.To predict the stability of the artificial island,settlement and deep horizontal displacement were monitored during the reclamation.The monitoring data indicate that the horizontal displacement at S3 was developing at a comparatively quicker pace,and followed by that at S5-S7.The horizontal displacement at the remaining measurement cross-sections were significantly less than these four cross-sections,indicating that the optimization of construction technique effectively guaranteed the stability of the cofferdam during reclamation.