南京长江第四大桥北锚碇沉井基础施工关键技术

Key Techniques for Construction of North Anchorage Caisson Foundation of the Fourth Nanjing Changjiang River Bridge

南京长江第四大桥北锚碇采用沉井基础,沉井尺寸为69.0 m×58.0 m×52.8 m,置于密实卵砾石层,工程地质条件复杂。沉井共分11节,第1节为钢壳混凝土沉井,其余均为钢筋混凝土沉井。采用打设砂桩和换填砂土复合地基加固法加固地基。在加固地基上现场拼装钢壳沉井节段,浇注第1节沉井混凝土。11节沉井分4次接高下沉,首次下沉采取水力吸泥机取土、降排水下沉,其余3次下沉采取空气吸泥机取土、不排水下沉。沉井下沉就位后按照4个分区的顺序逐区进行封底混凝土施工。施工监测表明,沉井下沉姿态、偏差均控制在规范标准之内。

The caisson in dimensions of 69.0 m×58.0 m×52.8 m is used for the foundation of the north anchorage of the Fourth Nanjing Changjiang River Bridge and is set in the dense pebble stratum where the geologic conditions are complicated. The caisson is composed of totally 11 sections with its first section a steel shell concrete and the rest of the 10 sections the reinforced concrete. At the site of the caisson, the ground was first reinforced by the combined reinforcement method of building sand piles and backfilling sand soil, the steel shells were then assembled on the reinforced ground and the concrete for the first section of the caisson was cast. The 11 sections of the caisson were extended in height and were sunk down in 4 times. For the first time sinking of the caisson, the soil in the caisson was air lifted out and the water there was discharged, and for the rest of the 3 time sinking, the soil was also air lifted out, but the water was not discharged. After the caisson was sunk in place, the tremie concrete for the bottom sealing of the caisson was cast area by area according to the four divided areas. The monitoring of the construction indicates that the sinking status and the offsetting tolerance of the caisson are all controlled within the provisions in the technical specification.