黏性土地区悬索桥锚碇沉井基础关键技术研究

Study on Key Technology of Anchor Caisson Foundation of Suspension Bridge in Cohesive Soil Area

怀来官厅水库特大桥主桥采用720 m单跨悬索桥,官厅水库为北京市一级水源保护区,桥位邻近既有铁路,施工条件复杂。两岸锚碇采用沉井基础,为黏性土地区大型陆地沉井,下沉难度大。沉井平面为倒圆角矩形,沉井高度为32、33 m,沉井基础设计施工的关键点是将沉井顺利下沉就位。悬索桥锚碇沉井可结合建设条件,适当增加沉井自重,降低施工难度,本桥沉井重率69.5 kPa。通过增加沉井重率,设置空气幕助沉措施,解决黏性土地区大型沉井的下沉难题。全高采用钢筋混凝土沉井,刃脚外包钢板,底节采用土模法施工,满足下沉要求的同时,提高了经济性。通过加强底节隔墙与井壁连接构造,优化顶节隔墙布置,提高下沉过程沉井底节、顶节的安全性。

The main bridge of Huailai Guanting Reservoir Bridge is a 720 m single span suspension bridge.Guanting reservoir is a first-class water source protection area in Beijing.The bridge site is adjacent to the existing railway,and the construction conditions are complex.Caisson foundation is adopted for anchorage on both banks,and it is a large land caisson in cohesive soil area and difficult to sink down.The plane of the open caisson is a rounded rectangle,and the height of the open caisson is 32 m and 33 m.The key point in the design and construction of caisson foundation is to allow the caisson to sink down smoothly.In view of the construction conditions,the dead-weight of the anchor caisson can be appropriately increased so as to reduce the construction difficulty.The weight ratio of the caisson of this bridge is 69.5 kPa.The problem of sinking large caisson in cohesive soil area is solved by increasing the weight ratio of caisson and setting up air curtain.Reinforced concrete caisson is adopted for the whole height,steel plate is wrapped around the cutting edge,and soil mould method is used for the bottom section to meet the sinking requirements and improve the economy.By strengthening the connection structure between the bottom partition wall and the caisson wall and optimizing the layout of the top partition wall,the safety of the bottom section and the top section of the caisson during the sinking process is improved.