Centrifugal model tests on characteristics of deep foundation pits in starting well of shield tunneling machine
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摘要: 为探究盾构机始发井深基坑开挖过程中周边土体的应力、变形和土压力分布规律，通过对工程原型进行概化，在典型土层条件下，采用停机-开挖-支护的模拟方式开展了方形基坑和圆形基坑两种方案共2组离心模型试验，从地连墙的弯矩和其后土体的水平位移、基坑外侧土压力分布以及地表沉降等角度，对比分析了两种盾构机始发井深基坑开挖过程的工程特性。结果表明：地面沉降随基坑开挖深度增大逐渐增加，形成沉降槽状；地连墙土压力变化呈非线性，随着基坑开挖不断深入的，离地表较近处的土压力逐渐变大，而深处的土压力则逐渐减小；在第5步开挖时2组模型地下连续墙水平位移均达到最大值，圆形基坑是方形基坑的1.4倍，同时地连墙的弯矩也达到最大值，圆形基坑比方形基坑小320 kN·m。研究成果可为深埋隧道深基坑的优化设计和开挖提供指导。Abstract: In order to explore the stress, deformation and soil pressure distribution of the surrounding soils during the excavation process of deep foundation pits in starting well of the shield tunneling machine, two sets of centrifugal model tests are conducted using the simulation method of shutdown excavation support under typical soil conditions, including square foundation pit and circular foundation pit, by generalizing the engineering prototype. The bending moment of the diaphragm wall and the horizontal displacement of the subsequent soil are analyzed A comparative analysis is conducted on the engineering characteristics of two types of shield tunneling machines during the excavation process of the deep foundation pits, including the distribution of soil pressure on the outer side of the foundation pit and surface settlement. The results show that the ground settlement gradually increases with the increase of the excavation depth of the foundation pit, forming a settlement trough shape. The variation of soil pressure on the diaphragm wall is non-linear. As the excavation of the foundation pit deepens, the soil pressure near the surface gradually increases, while the soil pressure at the deeper depth gradually decreases. In the fifth step of excavation, the horizontal displacements of the underground continuous walls in both models reach their maximum values. The circular foundation pit is 1.4 times that of the square foundation pit, and the bending moment of the underground continuous wall also reaches its maximum value. The circular foundation pit is 320 kN·m smaller than the square foundation pit. The research results can provide guidance for the optimization design and excavation of deeply buried tunnels and deep foundation pits.
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图 2 盾构机始发井地连墙模型
Figure 2. Model of ground wall connection for shield machine starting well
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图 4 方形和圆形基坑不同开挖步时地连墙水平位移
Figure 4. Horizontal displacements of diaphragm walls during different excavation steps for square and circular foundation pits
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图 5 方形和圆形基坑不同开挖步基坑地表沉降
Figure 5. Surface settlements of square and circular foundation pitsat different excavation steps
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图 6 方形和圆形基坑开挖时外侧土压力随开挖深度变化曲线
Figure 6. Curves of variation of external soil pressure with excavation depth during excavation of square and circular foundation pits
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