陡变水位深水桩基施工关键技术

Key Construction Techniques for Deep-Water Pile Foundation in Steeply-Variable Water Area

童庄河大桥主桥为(45+100+320+100+45)m双塔双索面混凝土梁斜拉桥,桥塔墩基础采用整体式矩形承台,其下布置11根2.8m、长63m的钻孔灌注桩。桥址河床陡峭,覆盖层松散、岩石破碎、多洞穴等,桩基施工期间水位变化达30m。为解决钢护筒精确着床、施工期间水位陡变的难题,采用"钢护筒+钻孔平台"相结合的平台系统进行桩基施工。施工平台系统由锚碇、拼装浮运系统、钢护筒、钻孔平台和导向架等组成。施工时,钻孔平台在驳船上拼装并浮运至墩位,每个平台利用2个10t岸锚和4个5t铁锚进行定位锚固,然后安装钢立柱定位导向架,插打钢护筒实现钻孔平台精确定位;利用8点提升方式进行钻孔平台提升,完成体系转换,形成固定钻孔平台;采用冲击反循环施工工艺完成钻孔施工。

The main bridge of Tongzhuang River Bridge is a two-pylon concrete girder cable-stayed bridge with spans of 45,100,320,100,and 45 m.The stay cables are fanned out in double cable planes.The foundation of the pylon pier,which is topped by integral rectangular pile cap,consists of 11,?2.8 m bored piles,63 m long each.The river bed at the bridge site is steep,with loose overburden,damaged rocks and numerous caves,and the water level change reaches up to 30 m during the pile foundation construction.To resolve the problem of accurate landing of steel casings and handle the situation of sudden change of water level during construction period,a platform system formed of steel casings and pile drilling platform was used to the pile foundation construction.The construction platform system is formed of steel anchor,assembly and floating system,steel casings,pile drilling platform and guiding frame.During the construction,the pile drilling platform was assembled on the barge and floated to the pier sites.Each platform was anchored by two bank anchorages with a capacity of 10 t each and four iron anchorages with a capacity of 5 t each.Then,the steel post position guiding frame was installed,and the steel casings were driven to realize the accurate positioning of the pile drilling platform.The pile drilling platform was lifted by way of eight-point lifting method,to realize the systematic transformation and form the permanent pile drilling platform.And the impact reverse circulation construction technique was used to complete the pile drilling construction.