某富水砂层深基坑悬挂式止水帷幕评估与研究

Study and evaluation for deep excavation with suspendedgroundwater cut-off curtain in water-sandy layer

针对某富水砂层基坑体量大、边界长、紧邻天然基础大断面管廊(结构变形控制要求高)的特点,采用多种方式获取了准确的富水砂层参数,并进行了悬挂式止水帷幕情况下管廊的沉降研究及评估。采用超深静力触探判定砂层密实程度,获得准确的力学参数并据此快速评估降水对周边地表沉降的影响;通过现场抽水试验进一步获得富水砂层的水文参数并验证沉降数据;然后采用获得的力学参数及水文参数,通过有限元计算精确分析不同止水帷幕深度情况下基坑降水对综合管廊变形的影响;最后,针对三轴搅拌桩在密实砂层钻进速度慢、工效低的问题,通过优化桩长及适当的设备改造,确保了顺利施工。本项目为富水砂层基坑止水帷幕的优化设计、施工提供了一套可行的评估思路,可为类似深基坑工程提供借鉴经验。

In response to the characteristics of a large deep excavation with long boundary and high deformation control requirements for a large cross-section urban utility structure in water-sandy layer,multiple methods are used to obtain accurate parameters of the water-sandy layer,and a study and evaluation of the settlement of the pipe gallery with suspended impervious groundwater cutoff was conducted.The compactness of the sand layer and obtain accurate mechanical parameters is determined by cone penetration test(CPT),then the impact of precipitation on surrounding surface settlement is quickly evaluated;hydrological parameters were further obtained through on-site pumping tests and settlement were verified;then the mechanical and hydrological parameters were used to analyze the deformation of the multi-purpose utility structure under different depths of curtains by FEM;finally,in response to the problems of slow drilling speed and low work efficiency of tri-axial mixing piles in dense sand layers,the prompt construction is ensured by optimizing the pile length and appropriate equipment modification.This project can be referred by the similar deep excavation projects.