深基坑开挖对坑底桩受力变形特性的影响研究

随着基坑开挖深度不断加大，基坑开挖过程对已施工坑底工程桩的受力和变形影响不容忽视，针对该问题，对深开挖条件下桩基进行了桩身内力及位移的工程现场实测。对比分析不同位置及不同长度的坑底桩基在开挖过程中的受力和变形规律。结合工程建立三维数值分析模型，基桩采用钢筋混凝土损伤模型，探究了基坑开挖深度、桩的相对位置等因素对桩身轴力、桩土侧摩阻力和桩身刚度的影响规律。结果表明：基坑开挖过程中，桩身受拉力作用；桩身混凝土在产生塑性应变前，桩身拉力随开挖深度增加逐渐增大；桩身混凝土应变超过极限拉应变后，拉力开始逐渐降低，桩身塑性区侧摩阻力变化显著。此外，坑底桩位置和桩长是影响其受力变形特性的重要因素。相同位置处，长桩的桩顶竖向位移更小；靠近基坑中心部位的桩顶竖向位移大，桩身塑性拉应变区较大。

Research on effect of deep excavation on force-deformation characteristics of piles in pit

With the increasing depth of foundation pit excavation, the influence of foundation excavation on the stress and deformation of piles in the pit bottom can not be ignored any more. In view of this problem, the field measurement of internal force and displacement of piles under deep excavation was carried out. The excavation induced stress and deformation of pit bottom piles with different lengths and in different locations were compared and analyzed. Based on the three-dimensional numerical analysis model with concrete damaged model for the reinforced pile, the effects of excavation depth and relative position of piles on the axial force, lateral friction resistance and stiffness of piles were studied. The results show that, during the excavation of foundation pit, the pile body is subjected to tensile force. Before the plastic stage, the tensile force of pile body increases gradually with the increase of excavation depth. When the concrete strain exceeds the ultimate tensile strain, the axial force gradually decreases, and the lateral friction in the plastic zone of pile body changes significantly. In addition, the location and length of the pile are important factors affecting the mechanical and deformation characteristics. At the same location, the vertical displacement at the top of the long pile is smaller. The closer to the center of the foundation pit, the larger vertical displacement at the top of the pile and the larger plastic strain zone of the pile body.