施工期间人工挖孔桩桩间土稳定性分析

Stability analysis of soil between manual digging piles during construction

为预防人工挖孔桩窜孔,探讨了桩间土失稳机制,分析了桩间土失稳时的位移特征,建立了桩间土稳定性分析的力学模型,推导了桩间土稳定系数及安全桩净距的计算公式,提出了窜孔防治措施建议。结果表明,桩间土失稳时,滑动土体位移平行于桩心连线,其宽度等于两桩桩径较小值;桩间土稳定系数与滑动土体宽度及埋深成反比,与桩净距成正比,随滑动层的抗剪强度及残余抗剪强度增大而增大,而滑动层厚度则存在一个最不利值,可通过试算确定;控制桩孔间的混凝土面高差、增大桩孔开挖净距、加强护壁,减少桩间土的扰动等是防治窜孔的有效措施。工程实例表明,桩间土稳定性评价方法合理、实用,可为黏性土场地的人工挖孔桩施工提供参考。

To prevent the accident of fleeing bore during manual digging pile construction, the instability mechanism of soil between manual digging piles is discussed; then the feature of displacement in instability is analyzed; a stability analysis mechanical model is established; formulas for the stability coefficient and critical value of pile spacing are derived; and some suggestions for fleeing bore prevention are provided. The results show that during the instability of soil between piles, the sliding soil displacement parallels to the line through the two pile centers and its width is equal to minimum of diameters of the two piles. While the most disadvantageous value of the thickness of the sliding soil could be determined by repeated calculation, the stability coefficient of soil between piles is inversely proportional to the width and the depth of the sliding soil, is proportional to the pile spacing, and rises with increasing of the shear strength and residual shear strength of the sliding soil. Controlling the concrete height difference between two pile holes, increasing the pile spacing, strengthening the lining structures, and reducing disturbance of soil between piles, are the most effective measures for fleeing bore prevention. Engineering practice has proved that the stability analysis method of soil between manual digging piles is reasonable and practical; so as to provide reference for manual digging pile construction in cohesive soil-based site.