长江砂层区域深基坑钢板桩围堰施工技术

Construction Techniques for Steel Sheet Pile Cofferdam in Deep Foundation Pit in Changjiang River Sand Zone

沌口长江公路大桥主桥为(100+275+760+275+100)m钢箱梁斜拉桥,2号墩位于长江砂层区域,砂层厚度达7m,常年水深5m以上。2号墩钻孔桩施工完成后,采用钢板桩围堰进行水中深基坑承台施工。钢板桩采用拉森Ⅵ(600mm×210mm)钢板桩(长24m),围檩系统共3层,由3HN700×300型钢、Φ1 000mm×10mm钢管、2HN588×300型钢等组成。钢板桩围堰采用"先支法"施工工艺,首先采用导向挂靴工艺,分层整体下放围檩系统,下放到位后插打钢板桩;然后水下吸泥,浇筑封底混凝土,待封底混凝土强度达到设计要求后,以控制钢板桩内外水头差的原理进行分级抽水,并对第一、第二层围檩系统进行完善及体系转换;第三层围檩施工完成后,进行最后一级抽水及第一层承台施工,完成第三层围檩体系转换后拆除第三层围檩,进行第二层承台施工。

The main bridge of Zhuankou Changjiang River Highway Bridge is a steel box girder cable stayed [）ridge with spans of 100, 275, 760, 275, and 100 m. The pier No. 2 is located in the sand zone of Changjiang River, where the thickness of the sand layer reaches up to 7 m and the wa ter depth is above 5 m all year round. After the completion of the bored pile construction of pier No. 2, the steel sheet pile cofferdam was used for the construction of the deep foundation pit pile cap. The steel sheet pile adopts the Larsen Ⅵ steel sheet pile with dimension of 600 mm×210mm, 24 m long. The waling system consists of three layers, which are formed of the 3HN700×300 section steel, φ1 000 mm×10 mm steel pipes and 2HN588×300 section steel. The steel sheet pile cofferdam was constructed by the pre supporting technique. First, the guiding drop in sockets were used to integrally lower the waling system layer by layer, and when the waling system was lowered into place, the steel sheet piles were driven. The following procedures were to dredge mud and cast the base sealing concrete under water. When the strength of the base sealing concrete reached the design requirement, water was pumped out stage by stage following the principle of controlling the difference of water level inside and outside of the steel sheet pile. The first and sec ond layers of the waling system were adjusted for perfection and made to finish systematic transfor mation. After the construction of the third layer of the waling, the last stage of water pumping was carried out and the construction of the first layer of pile cap began. When the systematictrans formation of the third layer of the waling system was completed, the third layer of waling was dis mantled, and the construction of the second layer of the pile cap began.