基于时间效应理论的软土深基坑变形分析

由于软土的蠕变特性,在基坑开挖过程中存在着时间效应。以宁波某基坑为工程背景,基于SSC模型并利用PLAXIS有限元软件对深基坑的开挖过程进行了数值模拟,分析了开挖工程中支护结构及基坑自身的变形特点。计算结果表明:基坑开挖时地连墙水平位移、地表沉降及支撑内力均随时间发展而增大,但相比之下,基坑隆起的流变效应不甚明显。其中不同工况对应地连墙水平位移最大值发生位置随开挖深度的增大而下降,而地表沉降最大值基本发生在距坑壁10 m位置,且地表沉降累计最大值与累积施工时间满足多项式函数关系;同时不同工况下地连墙弯矩、剪力随深度变化曲线趋势基本一致并呈"S"形。另外随着支撑结构的施加,地连墙水平位移和地表沉降的增加速率均受到一定限制,因此可通过及时施加支撑的方法抑制支护结构的变形及控制内力的急剧变化。上述结论可对宁波地区基坑开挖的施工提供理论指导,以保障施工过程的安全实施。

Analysis of Deformation of Deep Excavation in Soft ClayBased on Time-effect Theory

Time-effect exists in the process of deep excavation due to the creep property of soft soil.In this article,the excavation process of a deep excavation in Ningbo city is simulated using SSC model and finite element software PLAXIS,and the deformation characteristics of retaining structures and deep excavation are analyzed.Results revealed that the horizontal displacement of diaphragm wall,ground settlement and inner force of retaining structure increase with the increasing of construction time;while the rheological effect of foundation upheaval is not obvious.Secondly,the positions of the maximum horizontal displacement of diaphragm wall correspondingto various construction stages shift towards the deep with the increasing of excavation depth.However,the maximum ground settlement at different construction stages almost happens about 10m away from the pit wall.On this basis,an equation is established between cumulative maximum ground settlement and cumulative construction time.Moreover,curves of the bending moment and shear force of diaphragm wall vs.excavation depth at different construction stages are identical and display S-shape.Finally,support structure simpede the further development of the horizontal displacement of diaphragm wall and the ground settlement.The deformation of supporting structures and the sharp change of internal force could be effectively controlled by applying support in time.The conclusions offer guidance to the construction of deep excavation in Ningbo city to ensure the safety of construction process.