软土基坑开挖深度与空间效应实测研究

为了给软土基坑工程开挖的支护设计与施工提供参考，针对软土基坑开挖中普遍存在的开挖深度以及空间效应，考虑分区开挖与挡墙加固等有利因素的影响，以上海市五坊园基坑工程为背景，进行开挖过程中基坑及周围环境动态响应的追踪研究。采用现场设点实测的方法对施工过程中围护结构位移、支撑轴力、立柱隆沉及邻近管线位移的变化规律进行监测，并将实测数据与类似条件的软土基坑开挖工程进行对比，分析施工过程中软土基坑自身结构及周边管线的变形特性，探究开挖深度与空间效应对不同位置基坑结构的影响。研究结果表明：基坑施工对围护墙体及周边环境的影响具有明显的空间效应和深度效应；浅层土体开挖时（2 m深度范围内），基坑侧移空间分布主要受开挖顺序、土层性质和基坑阳角等因素影响；深层开挖时，基坑侧移体现出明显的空间效应；第1道支撑主要受土层流变影响，轴力在第2道支撑拆除阶段达到最大；由于底板硬化作用，第2道支撑轴力在底板浇筑阶段先增大后减小；基坑开挖卸荷会导致围护墙和立柱桩产生向上的位移，由于更加靠近基坑中心，立柱隆起值大于围护墙隆起值；基坑开挖深度越深，附近地下管线的沉降速率越大。

Observation on Depth and Spatial Effects of Deep Excavation in Soft Clay

To provide a reference for design and construction of excavation in soft clay, in allusion to the widely existing depth and spatial effects of deep excavation, considering the influence of zoned excavation and diaphragm walls enhancement, the dynamic response of excavation and adjacent environment was investigation the basis of a comprehensive instrumentation program of the third stage excavation engineering at Wufangyuan in Shanghai. The displacement of retaining walls, the axial forces of concrete bracing, the deformation of vertical columns, and the settlements of surrounding pipelines were monitored in site and compared with similar excavation cases. Through the comparison and analysis, the deformation characteristics of excavation, adjacent structures and the effects of excavation depth and construction sequence on excavation in different positions were also discussed. The results show that the excavation exhibit highly spatial and depth effects on diaphragm wall and surroundings. The spatial distribution of excavation during the process of excavation of the shallow soil layer (0~2 m below the ground surface) are mainly affected by the excavation sequence, the soil properties and the concave angle. Deep excavation may cause irreversible wall deflections, where corner effects are significant. The effect of soil creep on the axial force of the first strut is significant, so the axial force keeps continually increasing when the second strut was removed. Since the base slab may help the second strut to resist the pressure of the wall, the axial force of the second strut firstly increase and then decrease when the baseboard is casting. The displacement of diaphragm walls and vertical columns is produced by excavation load. Furthermore, the heaves of vertical columns are greater than those of walls during the excavation because of the smaller distance from the center of the excavation. The settlement rates of the pipelines increase with the increase of the excavation depth.