施工顺序对微型钢管桩加固既有基础变形的影响试验研究

微型钢管桩由于具有施工效率高、对周围环境友好等技术优点，被广泛应用于既有建筑物的增层改造、加固及纠偏工程中。施工顺序会影响加固或纠偏效果，甚至影响建筑物的安全，然而围绕施工顺序对微型钢管桩加固既有基础的变形特性影响的研究仍相对不足。基于透明土材料和粒子图像测速（Particle Image Velocimetry，PIV）处理技术，开展不同沉桩顺序（逆时针、顺逆时针结合、Z字形及对称形）下既有基础微型桩加固的可视化模型试验，分析加固过程引起的桩周土体位移场变化，以及不同沉桩加固顺序对既有承台的影响规律，并确定最优的加固方案。结果表明，在试验条件下，承台面下方的桩对桩周的土体有挤密作用，在承台周边压桩时，承台面下方的桩周围土体位移较小，相对于无承台情况影响范围缩小42%，最大位移缩小36%；对称加固顺序相对最优，施工过程中对既有基础的抬升位移仅为最不利加固顺序时的56%。

Experimental study on influence of construction sequence on deformation of existing foundation reinforced with micropile

Micro steel pipe pile is widely used in the reconstruction, reinforcement and rectifying of existing buildings considering that it is of high construction efficiency and environmentally friendly. The construction sequence would influence the effect of reinforcement or rectification and even the safety of the building. However, the research about influence of the construction sequence on displacement of the existing foundation reinforced by micro steel pipe piles is still relatively insufficient. Based on transparent soil material and particle image velocimetry (PIV) technology, this study performed the visual model test of reinforcing existing foundation via micro piles in different sinking orders (counterclockwise type, combined clockwise and counterclockwise type, Z type and symmetrical type), analyzed the displacement field of soil caused and the influence of different sinking orders on the cushion cap, pointed out the optimal strengthening scheme. The results indicate that under the test conditions, the pile under the cushion cap had a compacting effect on the surrounding soil. When the pile sanked around the cushion cap, the soil displacement around was less significant, and the soil disturbance zone was reduced by 42%, and the maximum displacement was reduced by 36% compared with the case of no cushion cap. The symmetrical reinforcement sequence was optimal, considering that the lifting displacement was only reduced by half.