黄土地区不同成孔方式灌注桩压浆前后承载特性

为了研究成孔方式对后压浆灌注桩承载特性的影响，分别对压浆前后的人工挖孔、旋挖成孔和冲击钻孔灌注桩进行了现场静载试验，分析了成孔方式对最终注浆量的影响，研究了不同成孔方式下灌注桩压浆前后沉降、极限承载力、桩侧阻力及桩端阻力的改善效果；探讨了不同成孔工艺对压浆过程和桩基承载特性的影响机制，考虑不同成孔方式和浆液上返高度，验证了《建筑桩基技术规范》(JGJ 94—2008)推荐的后压浆桩基极限承载力计算方法。研究结果表明:当理论注浆量相同时，实际最终注浆量从大到小依次为旋挖成孔桩、人工挖孔桩和冲击钻孔桩；压浆后，沉降特性的改善效果从好到差依次为冲击钻孔桩、旋挖成孔桩和人工挖孔桩；极限承载力的提高幅度从大到小依次为冲击钻孔桩、旋挖成孔桩和人工挖孔桩；压浆后，距桩端以上12 m范围内的桩侧阻力明显提高，提高幅度从大到小依次为冲击钻孔桩、旋挖成孔桩和人工挖孔桩；人工挖孔桩、旋挖成孔桩和冲击钻孔桩桩端阻力占总荷载的比例分别提升了17.05%、12.23%和15.10%，均表现出明显的端承摩擦桩特性；人工挖孔桩和旋挖成孔桩侧阻力和端阻力增强系数与《建筑桩基技术规范》(JGJ 94—2008) 基本接近，冲击钻孔桩则相差较大，表明灌注桩成孔方式对后压浆参数的选取和后压浆灌注桩的承载特性具有很大的影响。 

Bearing characteristics of cast-in-place piles with different hole-forming methods before and after grouting in loess area

Static load tests on manual digging piles (MDPs), rotary drilling piles (RDPs), and impact drilling piles (IDPs) before and after grouting were performed to investigate the effect of hole-forming method on the bearing characteristics of cast-in-place piles under post-grouting. The effect of hole-forming method on the final grouting quantity was analyzed. The improvement effects of pile settlement, ultimate bearing capacity, pile side resistance, and pile end resistance before and after grouting under different hole-forming methods were evaluated. The influence mechanisms of different hole-forming methods on the grouting process and bearing characteristics of the pile were examined. The methods for calculating the ultimate bearing capacity of post-grouting pile recommended by the Technical Code for Building Pile Foundations (JGJ 94—2008) were verified by comparing different hole-forming methods and the upper return height of the slurry. Research results show that the actual final grouting quantities range from large to small in the order of RDPs, MDPs, and IDPs when the theoretical grouting quantities are the same. After grouting, the improvement effects of settlement characteristic range from positive to negative in the order of IDPs, RDPs, and MDPs. The increasing ranges of the ultimate bearing capacity are from large to small in the order of IDPs, RDPs and MDPs. The pile side resistance improves within 12 m above the pile end after grouting, and the increasing ranges are in the order of IDPs, RDPs, and MDPs. The proportions of pile end resistances to the total loads of MDPs, RDPs, and IDPs increase by 17.05%, 12.23%, and 15.10%, respectively, indicating significant improvements in the characteristics of the end-bearing friction pile. The enhanced coefficients of side resistances and end resistances of MDPs and RDPs are close to those recommended in the Technical Code for Building Pile Foundations (JGJ 94—2008), whereas those of the IDPs are slightly different. Therefore, the hole-forming method of cast-in-place pile significantly influences the selection of post-grouting parameters and the bearing characteristics of cast-in-place piles. 6 tabs, 7 figs, 31 refs.