桥梁灌注桩开式压浆难以控制注浆区域、注浆压力和注浆量,注浆效果不稳定、单桩承载力波动大。为提升桩基后压浆的可靠性,提出一种新型桩底复合式后压浆技术,通过在桩底安装中空环形钢板胶囊,采用“外—内—外”3次注浆加固桩端土体。为探明该技术对桩基承载力的提升效果,依托在建汾石高速S340跨线桥工程开展2根试桩的桩端复合式后压浆作业,研究压浆过程中注浆压力、注浆量和桩顶位移的动态变化情况,并对注浆效果进行弹性波CT测试;然后开展了采用桩端复合式后压浆和不注浆两种工况下的桩基静荷载对比试验。结果表明:桩底复合式后压浆可有效消除桩底沉渣,形成桩端扩大头,桩基承载力提升34.1%,桩端阻力增强系数为1.70,浆液影响范围内桩侧摩阻力增强系数为1.32~1.37。
The open grouting of bridge cast-in-place piles is difficult to control the grouting area, grouting pressure and grouting amount. The stability of grouting effect is poor and the bearing capacity of single pile fluctuates greatly. In order to improve the reliability of post grouting of pile foundation, a new type of composite post grouting technology at pile bottom is proposed. By installing hollow annular steel plate capsules at pile bottom, the soil at pile end is strengthened through the composite inside and outside of the capsule. To reveal the improvement effect on the bearing capacity of pile foundation, composite post-grouting operation of two test piles was conducted at S340 overpass bridge project of Fenshi Expressway under construction. The dynamic changes of grouting pressure, grouting volume and pile top displacement during grouting were analyzed, and the grouting effect was tested by elastic wave CT. Then, the vertical static load tests of pile foundation were carried out under post-grouting and non-grouting conditions. The results show that the composite post-grouting at the pile bottom can effectively eliminate the sediment at the pile bottom and form an expansion pile end. The bearing capacity of the pile foundation is increased by 34.1%. The pile end resistance enhancement coefficient is 1.70, and the pile side friction enhancement coefficient is 1.32~1.37 within the influence range of the slurry.
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