基于事故分析的深基坑承压水突涌机理研究

承压水突涌事故多沿基坑底穿透相对隔水层的钻孔发生,而围堰结合注浆加固是主要处理方法。首先介绍杭州钱江新城区域近年发生的5起承压水突涌事故及其处理方案,然后将事故简化为轴对称问题进行分析,利用事故发生前后钻孔内竖向渗流平衡条件研究事故原因,根据基坑开挖到底时加固体重力平衡和加固体边缘渗透平衡条件分析加固范围,最后通过围堰稳定性分析确定围堰高度和宽度。结合典型地层结构和地区经验,分析结果表明:相对隔水层有钻孔时,事故区域基坑最大开挖深度依次由钻孔内竖向渗透平衡、加固体边缘渗透平衡和坑底土层重力平衡决定;围堰高度由承压水头和竖向渗透平衡决定,围堰宽度由开挖面水平渗透平衡和围堰边坡稳定性控制。

Analysis and Treatment of Inrushing Accidents in Deep Excavation

The confined water inrushing accidents were usually caused by drilling holes in the foundation while the effective and used widely treatment method was cofferdam and grouting. After five accidents occurred in Hangzhou CBD recently were introduced, an axisymmetric model was proposed to calculate the maximum excavation depth according to seepage equilibrium of sand and gravitational equilibrium of the grouted body. Based on typical strata and local experience, the relationship between confined water pressure and maximum excavation depth was investigated and the dominant factors were in order vertical seepage equilibrium, seepage equilibrium around the grouted body and gravitational equilibrium of pit bottom. Cofferdam height was determined by confined water head and vertical seepage stability. Cofferdam radius was obtained by its slope stability and seepage equilibrium along the excavation surface.