临近既有铁路线大型钢筋混凝土沉井施工技术

Construction Techniques for Large-Scale Reinforced Concrete Caisson Near to Existing Railways

官厅水库特大桥为主跨720m的单跨悬索桥。大桥南岸锚碇基础为33m高全钢筋混凝土沉井结构,标准平面尺寸为56m×50m。沉井中心距离京包铁路线仅60m,墩位处地质结构主要为粉质黏土和圆砾土。为对既有铁路线进行防护,采用单排钻孔灌注桩作为防护桩,在沉井施工之前完成防护桩的施工。沉井接高之前直接在地面根据沉井刃脚仿形开挖沟槽,沉井底节采用土模法在沟槽内安装模板和绑扎钢筋进行接高,底节完成后沉井采用翻模法正常接高,单次接高3m,接高到15m后开始第1次下沉施工。沉井共分2次下沉施工,进入地下水5m前采用干挖取土下沉,之后采用水下吸泥取土下沉。下沉施工采用潜水泵水下高压射水辅助吸泥,空气幕实施助沉。施工过程快速、平稳有序,确保了铁路路基的稳定,沉井按设计要求下沉到位。

The Guanting Reservoir Bridge is a single span suspension bridge with a main span of 720 m.The foundation of the south anchor block is a 33 m-high reinforced concrete caisson structure,with standard plan dimension of 56 mby 50 m.The center of the caisson is only 60 mto the Beijing-Baotou Railway.The ground at the piers is formed of silty clay and round gravels.To protect the existing railway,a single row of bored piles were driven to form the protective piles,which were installed before the caisson construction.Before the elongation of the caisson,trenches were directly cut on the ground according to the shapes of the caisson cutting edges.The base lift of the caisson was extended by installing formwork inside the trenches by soil model method and banding reinforcement.Once the base lift was completed,the caisson was extended normally by using climbing formwork,extending 3 meach time.When the caisson was extended to 15 m,it was sunk for the first time.The sinking construction of the caisson involved two phases,it was sunk by digging soil before reaching the position 5 mbelow the water,and then sunk by dredging.During the second phase sinking,the submerged pump was used to spray high-pressure water to assist mud dredging.And the sinking of the caisson was also assisted by air curtains.The construction was carried out rapidly and smoothly,to ensure the stability of the ground of the railway.The caisson was sunk into position in accordance with the design requirements.