南京大胜关长江大桥主墩深水基础施工关键技术研究

Research of Key Techniques for Construction of Deep Water Foundations of Main Piers of Dashengguan Changjiang River Bridge in Nanjing

南京大胜关长江大桥6～8号主墩基础采用超大型钢吊（套）箱围堰施工。在水文地质条件复杂的潮汐河段，钢吊（套）箱采用气囊法下水、浮运就位，无导向船重锚精确定位，围堰挂桩，内支撑桁架兼作钻孔平台，接高围堰，在重力大于浮力的可控状态下，实现围堰整体下放着床及河床内下沉第2次定位挂桩等施工方案。着重介绍超大型钢围堰气囊法断缆整体下水技术，钢吊箱无导向船重锚精确定位技术，超大型钢吊（套）箱下放、着床、下沉控制技术等基础施工关键技术。

The foundations of main piers No. 6 - No. 8 of Dashengguan Changjiang River Bridge in Nanjing were constructed by the very huge steel boxed cofferdams. In the tidal river reach of complicated hydrologic and geologic conditions, the cofferdams were launched by the air bag method, floated to the pier sites and accurately positioned there by heavy anchors without the aid of guiding barges. The cofferdams were then set on the piles, the bracing trusses inside the cofferdams were concurrently used as the boring platforms and the cofferdams were extended in height. In the controllable state that the gravity was greater than the buoyancy, the construction schemes for lowering the integral cofferdams down to the riverbed, sinking the cofferdams into the riverbed and the second time positioning and setting the cofferdams on the piles were well realized. This paper mainly deals with the key techniques for construction of the foundations, inclu- ding those of launching the integral huge cofferdams by the air bag method and by cutting anchor ropes, accurately positioning the cofferdams by heavy anchors without the aid of guiding barges, lowing, landing on riverbed and sinking control of the cofferdams.