上海深古河道区地铁车站基坑变形及相关问题

Deformations and Problems in a Subway Station Excavation in Deep Paleochannel Region in Shanghai

深厚软土区的深基坑工程仍然具有较大的挑战性。本文介绍了上海地区软粘土厚度较大(40 m以上)的深古河道区某地铁车站基坑(开挖深度17.6 m)的地表沉降、连续墙侧向位移、立柱隆起和支撑内力的特征。该车站标准段基坑地表最大沉降δv与开挖深度H的比值δv/H在0.3%~0.6%;地下连续墙最大侧向位移δhm与开挖深度H的比值在0.17%至0.46%之间,开挖至12 m以后侧向位移明显加大,部分位置超过报警值(δhm/H = 0.4%),并出现踢脚迹象;立柱隆起明显,开挖至坑底时的最大隆起量在60~80 mm,远超出隆起量为20 mm的设计条件。较大的立柱隆起使第一道钢筋混凝土支撑处产生拉力并产生裂缝,影响了支撑轴力的分布以及支撑的稳定性。坑底隆起的具体机理以及立柱桩隆起的分析方法和控制措施是该类地质条件下深基坑工程需重点解决的问题。

There are still big challenges in the deep excavation in soft clay area.The ground settlement,lateral displacement,pillar uplift and supporting internal force of a subway station in deep paleochannel region with a relatively large thickness of soft clay(over 40 m)in Shanghai are introduced.For the standard segment,the ratio of the surface maximum ground surface settlement to the excavation depth(δv/H)is 0.3%-0.6%.The ratio of the maximum lateral displacement of the underground diaphragm wall to the excavation depth(δhm/H)is 0.17%to 0.46%.When the excavation depth exceeds 12 m,the lateral displacement increased significantly,exceeding the warning value(δhm/H=0.4%),and showing signs of kicking in some parts.The uplift of the pillars is significant and they are in the range of 60 mm to 80 mm,which is much larger estimated value of 20 mm.The uplift causes the first reinforced concrete strut to generate tension and cracks,which affects the distribution of forces of the struts and the stability of the supporting system.The mechanism of the bottom uplift and the analysis method and control methods of the pillar uplift are the key issues needed to be solved in the subway station excavation under this kind of geological conditions.