临近基坑开挖复合地基侧向力学性状离心试验研究

临近基坑开挖引起复合地基CFG桩变形和内力改变，现有理论缺乏对该问题的研究。通过开展离心模型试验，对临近基坑开挖条件下，复合地基变形、CFG桩内力和变形、土压力等分布和变化规律进行深入分析。结果表明：开挖引起CFG桩弯矩增大，近基坑桩增幅明显|开挖引起桩土不同步沉降，导致CFG桩上刺入褥垫层，桩受到褥垫层的“嵌固拉结”作用，同时远基坑桩、褥垫层、加载气囊一起提供了“摩擦拉结”作用，从而在近基坑桩上出现负弯矩|而远基坑处不均匀沉降小，“嵌固拉结”作用小，且“摩擦拉结”作用是利于正弯矩产生，桩上未出现负弯矩|开挖引起支护背后土压力分为增长区和减小区两部分，在上部土体中，土体卸荷，土压力减小，而下部土体受支护挤压，土压力有所增大|开挖引起地表沉降呈指数形式，临近基坑地表沉降最大，在显著变形区域内，支护水平位移基本呈直线形式，各阶段最大水平位移均出现在支护顶端|开挖引起的CFG桩水平变形大小和范围随距基坑边距离的增大而减小。

Lateral mechanical behavior of composite ground due to adjacent excavation: centrifuge model test

 For deformations and internal forces of CFG piles in composite ground due to excavation of adjacent foundation pit, it is difficult to deal with such problems based on existing theories. A centrifuge model test has been carried out to study the change law of deformations and internal forces. Research results show that adjacent excavations may result in the increase of bending moment of CFG piles| the closer the CFG pile is to the foundation pit, the greater the increase of bending moment is. The excavation may also lead to ground surface settlement, but the settlements of soil and piles may not be synchronous. The CFG piles may penetrate upwards into the cushion layer, which provides the embedding and tie roles for the piles. The piles far from the foundation pit provide anchorage effect for those piles near the foundation pit through the friction between the loading gasbag and the cushion. The combined effects lead to the negative bending moment in those piles near the foundation pit. However, negative bending moments in the piles far from the foundation pit shall be small because in these locations, the differential settlement is generally small and the penetration phenomenon is not obvious. Earth pressure zone behind retaining wall can be divided into the decrease part and increase part. For the upper part, the earth pressure may decrease due to the unloading of soil, while for the lower part, the earth pressure may increase due to compression of retaining wall. The ground surface settlement caused by excavations has the form of exponential function, which is often called Peck’s curve. In the region with significant deformation, the horizontal displacement of retaining wall is basically linear, and the maximum value of displacement generally appears at the top of retaining wall in different stages. The magnitude and range of horizontal deformation of CFG pile due to excavation may decrease with the increase of its distance to the foundation pit.