软土中注浆与未注浆抗拔桩受力性状对比试验研究

在杭州萧山一工地未注浆与注浆试桩抗拔静载试验的基础上,发现抗拔桩经过桩端后注浆可显著减少桩端位移,极限抗拔力至少提高25%,最大桩身拉伸量占桩顶上拔量的91.5%。注浆与未注浆桩的桩身轴力都随深度逐渐减少,桩端轴力始终为0;浆液上返高度16.9m范围内注浆桩侧摩阻力有较大幅度的提高,最大提高幅度为83.3%;在利用浆液上返高度公式计算注浆抗拔桩竖向增强体高度和考虑桩身自重的基础上,提出桩端后注浆抗拔桩承载力的估算公式。通过反分析计算,未注浆桩抗拔折减系数的取值范围为0.65～0.80,注浆桩侧阻力增强系数的取值范围为1.33～1.83,计算方法与结果可供初步设计与实际工程使用。

EXPERIMENTAL STUDY OF BEHAVIOR COMPARISON OF GROUTED AND NON-GROUTED UPLIFT PILES IN SOFT SOIL

Based on the uplift static test of grouted and non-grouted uplift piles at a building site of Xiaoshan in Hangzhou area，it¢s found that pile-end post grouting technology can significantly reduce the pile tip settlement and increase the ultimate uplift resistance of pile. The ultimate uplift resistance of the pile with post-grouted is 1.25 times of the pile without post-grouted and the maximum tension value of pile shaft is about 91.5% of the displacement at the pile head. The axial forces of grouted pile shaft and non-grouted pile shaft both decrease gradually with depth and the measured end axial forces of piles are near zero during the whole loading cycle. The friction resistance of grouted pile within the climb height of grouts of 16.9 m has a large increase and the maximum value is 83.3%，because the mudcake near the pile end is solidified by grouting and the larger friction resistance are mobilized. Based on the vertical enhancement body height of grouted uplift piles calculated by the formula of climb height of grouts，a new simple formulation for calculating the ultimate bearing capacity of uplift piles with pile-end post grouting is proposed by considering dead weight of piles. Through the back analysis and calculation，it is shown that the value range of the uplift reduction coefficients of non-grouted piles is 0.65–0.80；and the value range of lateral resistance enhancement coefficients of grouted piles is 1.33–1.83. The calculation method and its results can be applied to the preliminary design and practical engineering.