薄壁锥端注浆微型钢管桩抗拔承载特性的现场试验

Field Test on the Uplift Bearing Characteristics of Thin-walled Cone-end Grouting Micro-steel Pipe Pile

解决新时期电网“绿色建设”的需求,研发并应用新型环保型杆塔基础是电网建设中的首要任务之一。本文提出一种改进的薄壁锥端注浆微型钢管桩,通过现场试验,研究该类钢管桩的抗拔承载特性。以双楼—交河220 kV线路工程为背景,设计出159和203 mm两种桩径、5和8 m两种埋深、注浆与不注浆两种条件,共18根钢管桩,开展18组试验桩的现场抗拔承载特性试验,对比分析了注浆作用对不同型号抗拔桩荷载位移曲线、抗拔承载力及桩周土体破坏模式的影响;基于现场试验获取的桩土界面破坏机制,建立桩土体系的有限元模型,对钢管桩上拔变形破坏过程进行数值模拟分析,重点佐证了现场试验中得出的桩土界面破坏模式;通过测试注浆前后桩周土体的抗剪强度参数和微观结构,分析注浆作用对桩周土体影响的宏微观机制。结果表明:1)注浆前后钢管桩荷载位移曲线由陡变型转变为缓变型,塑性变形特性增强;2)注浆前后,钢管桩抗拔承载力提高59%~148%,提高幅度与其长细比呈负相关;3)未注浆钢管桩发生破坏时,地表土体鲜见裂缝,桩体近乎被抽出,注浆钢管桩破坏时地表土体出现径向与环向裂缝;4)注浆过程中的浆液向土体空隙中不断渗透,充填了大量空隙,从而加固了桩周土体,最终在钢管桩周围形成水泥固结体,并与桩周土体之间形成剪切面,这一结论同时得到数值模拟结果的佐证。注浆作用对钢管桩抗拔承载力的影响机制主要体现在有效剪切面积的加大和桩周土体侧摩阻力的提高两个方面。工程应用表明,该桩型具有施工周期快、承载力高、对周围环境破坏小的优点,在双楼—交河220 kV线路工程中应用效果良好。

To meet the demand for green construction of power grids in the new era,it is urgent to develop and apply a new type of environment-friendly foundation for power grid projects.For this purpose,an improved thin-walled tapered-end grouted miniature steel pipe pile was proposed,and the uplift bearing characteristics of this pile were studied through field tests.With the project background of the 220 kV line Shuanglou—Jiaohe Dongguang north substation,18 steel pipe piles with two pile diameters of 159 mm and 203 mm,two burial depths of 5 m and 8 m were designed under two conditions of grouting and no grouting.The effects of grouting on the load–displacement curves,uplift bearing capacities,and soil failure modes for different test piles were analyzed through on-site uplift bearing characteristic tests.Based on the failure mechanism of pile–soil interface obtained through the field tests,a finite element model incorporated the pile–soil interaction for the tests was established,and the uplift deformation and failure process of the steel pipe pile was numerically simulated and analyzed.The simulation results showed that the failure modes of the pile-soil interface were consistent with the field tests.By comparing the shear strength parameters and microstruc-ture of the soil around the pile before and after grouting,the macroscopic and microscopic mechanism of the influence of grouting on the soil around the pile was analyzed.The test results are as follows:1)The load-displacement curve of steel pipe pile changed from steep drop type to slow change type after grouting,and the grouting enhanced the ability of the pile foundation to resist plastic deformation.2)The uplift capacity of steel pipe pile increased by 59%~148%after grouting,and the increase range was negatively related to the slenderness ratio of test pile.3)There were few cracks in the surface soil at the failure state of uplift tests for the non-grouting steel pipe piles.The pile body was almost extracted,and the surface soil appeared radial and circumferential cracks at the failure state of the grouting steel pipe piles.4)Many voids in soil were filled in the process of grouting,which improved the soil strength around the pile.Cement consolidation was formed around the steel pipe pile after grout-ing,and a shear surface was formed between the cement consolidation and soil.This conclusion was also supported by the numerical simulation results.The influence mechanism of grouting on the uplift bearing capacity of steel pipe pile was mainly reflected in the increase of shear area and side friction of soil around the pile.The engineering application showed that the proposed steel pipe pile had a short construction period,a high bearing capacity,and a low impact on the surrounding environment.These steel pipe piles have been well popularized and applied in the 220 kV line project Shuanglou-Jiaohe Dongguang north substation.