深中通道伶仃洋大桥东锚碇基坑支护施工关键技术

Key Construction Techniques for Foundation Pit Supporting Structure of East Anchor Block of Lingdingyang Bridge

深中通道伶仃洋大桥为主跨1666 m的全飘浮钢箱梁悬索桥,该桥东锚碇为重力式锚碇,采用8字形地下连续墙基础作为基坑开挖施工的支护结构。东锚碇基坑支护结构采用海中筑岛围堰的总体方案施工。东锚碇基坑支护结构施工前,在海中首先采用锁扣钢管桩及工字型钢板桩组合的围堰方案筑岛形成施工陆域,结合河床表层清淤、砂石垫层换填、插打塑料排水板等措施对筑岛陆域进行地基处理;待筑岛地基沉降稳定后,地下连续墙采用“旋挖引孔+铣槽”的复合成槽工艺施工;地下连续墙施工后,基坑采用岛式法分12区(平面)、14层(竖向)进行阶梯形开挖,同时采用同步降排水措施(设6个降水井、6个集水井)进行基坑开挖施工。

The Lingdingyang Bridge of Shenzhen-Zhongshan Link is a full-floating suspension bridge with a main span of 1666 m.The stiffening girder consists of steel box girders.The east anchor block is a gravity anchor,during the foundation construction of which,the"8"shaped diaphragm walls were built as the supporting structure to protect the excavation of the foundation pit.And an artificial island was built to facilitate the supporting of the foundation pit of the east anchor block.Before the construction of the foundation pit supporting structure of east anchor block,interlocked steel piles and I-shaped steel sheet piles were used together for the formation of the artificial island,so as to divert the offshore construction to land.The subgrade of the artificial island took form after a series of works,including river bed dredging,placement of sandstone cushion,and plastic dewatering plates driving.Once subgrade settlement of the artificial island tended to be stable,the construction of the diaphragm walls begun,and the trenches were dug by the technique of rotary digging,hole guiding and trench milling.When the diaphragm walls took form,the foundation pit was divided into 12 zones(in plan)and 14 layers(vertically)for the laddered excavation,and the excavation was also aided by using the synchronized dewatering measures,during which,a number of 6 dewatering wells and 6 sump wells were used.