软土地基微型桩抗拔试验研究

微型桩具有布置形式灵活,施工机械小型化,经济环保等优点,针对杆塔基础交通不便、环保要求高、地质情况差等工程特点,微型桩的优势在杆塔基础中能够得到充分发挥。承受上拔荷载是杆塔基础的主要功能之一,而以往对软土地基上微型桩抗拔特性的研究较少。通过软土地基中微型桩单桩和群桩的抗拔试验,研究施工工艺对微型桩单桩抗拔承载力的影响,实测单桩桩身轴力和桩侧摩阻力的分布,研究微型桩荷载—位移特性、群桩效应系数等。试验结果表明采用二次注浆工艺能显著提高微型桩抗拔极限承载力,有效地减小抗拔桩位移;由于二次注浆对桩周土体加固作用,群桩的荷载–位移曲线呈"缓变型",桩土共同作用的群桩效应明显,实测群桩效应系数相对较小,这对于软土地基上杆塔基础的设计具有参考价值。

Field test on uplift behavior of micropiles in soft ground

Micropiles have the virtue of flexible layout, economical construction, environmental protection and machinery miniaturization. These piles are especially suitable for transmission tower foundation due to inconvenient traffic, higher environmental requirement and complex geological condition. Being subjected to pullout is one of main functions of transmission tower foundation, but there are few researches on the characteristics of micropiles pullout behavior in soft ground. By the pullout tests of single micropile and group piles in soft ground, the shaft and lateral friction force of single piles are measured, and the influences of construction technology on uplift capacity of single micropile, the characteristics of load-displacement of micropiles and the coefficient of group effect and so on are studied. The test results indicate that the compaction of soil from twice pressure groutings can raise the ultimate uplift capacity of micropiles obviously and reduce the displacement effectively. For twice pressure groutings can reinforce the soil around the piles, the load-displacement curve of group piles appears “gradually varying type”, the measured coefficient of group effect is relatively small, and the group effect is obvious. These findings have reference value for designing transmission tower foundation in soft ground.