南昌红谷隧道临江富水砂层干坞基坑防渗墙施工技术

南昌红谷隧道干坞基坑深16 m,临赣江最近距离仅15 m,水位变化幅度达3~13 m,砂层渗透系数达120 m/d,防渗体系施工处于工期关键线路,防渗体系施工质量是实现基坑开挖、沉管预制、浮运、沉放等工期目标的重要保证。文章通过对塑性混凝土配合比、槽壁加固、成槽工艺、泥浆性能指标、清孔换浆、混凝土浇筑及墙体检测等的思考,提出了临江富水砂层干坞基坑防渗墙施工中三轴搅拌桩槽壁加固、配合比试配验证、"两钻两抓"成槽工艺、超声波仪成槽检验、高密度电法墙体检测以及膨润土泥浆性能指标、加强混凝土过程控制等主要施工方法和技术措施。通过在南昌红谷隧道临江富水砂层干坞基坑中的应用,证明塑性混凝土防渗墙止水防水效果非常好,为基底处理及沉管预制施工创造了良好的条件。

Construction Technology for Anti-seepage Wall of Foundation Pit of Dry Dock in Water-rich Sand Strata Adjacent to River: Case Study on Dry Dock of Honggu Tunnel in Nanchang

The foundation pit for the dry dock of Honggu immersed tunnel in Nanchang is 16 m deep and is only 15 m away from Ganjiang river at the closest position. The foundation pit is located in sand strata with 120 m/d permeability and 3~13 m water level fluctuation. The construction of the anti seepage system of the foundation pit is on the critical path of the project and the quality of the anti seepage system has great impact on the excavation of the foundation pit and on the prefabrication, transportation and immersing of the tunnel tubes. In the paper, the construction technologies for the anti seepage walls, including the reinforcement of the slot wall, the mixing proportion of the plastic concrete, the slot cutting by “two rotary drilling machines and two hydraulic grabbing machines” mode, the slot detection by ultrasonic waves, the anti seepage wall inspection by high density electric method, the performance of the bentonite slurry and the concrete casting, are studied. These technologies have been applied in the construction of the above mentioned anti seepage walls and good effects have been achieved. 