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介绍了杭州深厚软黏土中深度为14.85～17.35 m、采用密排连续排桩作为围护墙的大型多层支撑基坑工程监测实例。实测内容包括基坑施工过程中围护墙与土体水平位移、周围地面沉降、内支撑轴力、土压力和孔隙水压力等。研究表明:软黏土中大型基坑的水平位移明显大于狭窄基坑,基础底板施工期间基坑的“蠕变”现象明显,开挖深度、空间效应、隔断墙的设置、坑壁临近既有地下室等均是影响基坑水平位移的重要因素;坑外横向地表沉降呈抛物线型分布,沉降影响范围约为开挖深度的2.5倍,最大沉降位于坑外约0.67倍挖深处,最大沉降与最大水平位移关系约为vmax hmax 0.6,坑外纵向沉降大致呈马鞍形,沉降最大值位于基坑中部附近,纵向沉降影响范围大于基坑开挖范围;多层支撑支护结构中各层支撑的轴力随开挖和拆撑工况的变化而动态调整,第2层支撑轴力明显大于其它2层支撑;深厚软黏土中多支撑支护结构的土压力分布在支撑深度范围表现出“土拱”效应;随开挖的进行坑外土体的孔压逐渐减小,由于开挖卸荷产生了负超静孔压。
This paper introduces an example of monitoring large-scale multi-storey support foundation pit with depth of 14.85 ~ 17.35 m in deep thick soft clay in Hangzhou, using continuous rows of piles as retaining wall. The measured contents include the horizontal displacement of retaining wall and soil, the surrounding ground subsidence, the axial force of inner support, the earth pressure and the pore water pressure during the construction of the foundation pit. The results show that the horizontal displacement of large foundation pit in soft clay is obviously larger than that of narrow foundation pit. The phenomenon of “creep” of foundation pit is obvious during the construction of foundation slab. The excavation depth, space effect and partition walls are set. There are basement and so on are the important factors affecting the horizontal displacement of the pit; lateral settlement of the surface of the pit is parabolic distribution, the impact of settlement is about 2.5 times the depth of excavation, the maximum settlement is located outside the pit about 0.67 times the depth of excavation, the maximum settlement And the maximum horizontal displacement is about vmax hmax 0.6. The vertical settlement outside the pit is roughly saddle-shaped, and the maximum settlement is located near the middle of the pit. The influence range of longitudinal settlement is larger than the excavation range of the foundation pit. Of the axial force with the excavation and demolition support dynamic changes in the dynamic conditions, the second layer of support axial force was significantly greater than the other two-story support; deep soft clay multi-support structure of the earth pressure distribution in the support depth range shows “Soil arch ” effect; with the excavation carried out outside the pit hole pore pressure decreases gradually, due to excavation unloading negative negative pore pressure.