富水砂层深基坑支撑轴力发展规律现场实测分析

Field Measurement Analysis of the Support Axial Force Development Law for the Deep Excavations in Groundwater-rich Sand Layer

以钱江隧道江南盾构试验井基坑为工程背景,结合该地区若干类似地层中深基坑现场实测数据,着重探讨富水砂层地区深基坑支撑轴力、土压力的分布与发展规律。研究结果表明:在富水砂层地区,支撑轴力保持稳定,基坑呈现出明显的时间效应。受空间角效应的影响,最小支撑轴力出现在基坑角部,最大支撑轴力出现在基坑纵向中部附近。本工程选用的支撑系统能有效限制围护结构侧移。富水砂层深基坑围护结构侧向土压力与深厚软黏土地层之间存在显著差异,大长宽比、大尺度深基坑表观土压力包络线的峰值为0.45_(γ)H_(e),出现在开挖面以下(0.18~0.75)H_(e)处。采用Terzaghi和Peck、Tschebtarioff以及日本土木学会提出的预测模式将显著低估大长宽比或大尺度的深基坑表观土压力峰值。

Taking the Qianjiang Tunnel South Shield Test Well foundation pit as the background,combined with on-site measurement data of deep excavations in several similar strata in the area,this paper focuses on exploring the distribution and development law of axial support and soil pressure of the deep excavation in groundwater-rich sand layer.The research shows that,in groundwater-rich sand layer,the support axial force remains stable after construction,and the excavation exhibits a significant time effect.Due to the influence of spatial corner effect,the minimum support axial force appears at the corner of the excavation,and the maximum support axial force appears near the longitudinal center of the excavation.The support system selected for this project can effectively limit the lateral displacement of the retaining structures.There is a significant difference between lateral soil pressure on retaining structures of the deep excavation in groundwater-rich sand layer and those in thick soft clay layer.For large aspect ratio or large-scale deep excavation,the peak value of apparent soil pressure envelope line is 0.45γHe,appearing below the excavation face at 0.18~0.75 He.The prediction models proposed by Terzaghi&Peck,Tschebtarioff,and Japanese Civil Engineering Society significantly underestimate the peak value of the apparent soil pressure on large aspect ratio or large-scale deep excavation.