黏土中桩端后注浆单桩抗压承载特性室内模型试验研究

Indoor Model Tests on the Compressive Bearing Behavior of a Single Pile in Clay with Pile End Post-Grouting

参照现场桩端后注浆工艺的基础上,采用室内模型试验和自主研发的模型桩钻机以及注浆装置研究黏土中不同桩端注浆量下5根模型钻孔灌注桩竖向抗压承载特性,并通过后续土体开挖,分析桩端后注浆浆液上返高度和浆液在土体中的扩散模式.试验结果表明:与未注浆试桩相比,黏土中不同桩端注浆量下试桩极限承载力提高率为37.5%~112.5%,承载力提高幅度与注浆量呈正相关;注浆试桩桩端以上浆液上返段深度范围内轴力明显小于未注浆试桩,且轴力随着注浆量的增大而减小;桩顶荷载较小时,在浆液上返段深度范围内,4根不同注浆量试桩平均侧摩阻力略大于未注浆试桩且增长幅度受注浆量影响很小;随着桩顶荷载增大,该深度范围内注浆试桩桩侧平均摩阻力远大于未注浆试桩且其值随着注浆量的增大而增大;在相同注浆压力条件下,不同桩端注浆量主要影响桩端浆液上返深度范围内桩身侧摩阻力值大小,对上返高度影响较小,桩端后注浆浆液上返高度约为桩端以上14倍桩径;未注浆试桩表现出摩擦端承桩的特性,注浆试桩表现出端承摩擦桩的特性;在同一桩顶荷载下不同注浆量试桩桩端阻力发挥比例随着注浆量的增大而减小.通过开挖分析得出黏土中桩端后注浆主要通过浆液压密和劈裂作用于桩端和桩侧土体进而改善基桩承载特性.

On the basis of the post-grouting process of the field pile test,the compressive load behaviors of five different pile end post-grouting volumes of model bored piles were studied through indoor model tests,a self-developed model drilling rig,and grouting devices.The height of grouting returned and the diffusion mode of grout in the soil were analyzed by soil excavation.The test results show that the bearing capacity increase rates of the post-grouting pile range from 37.5%to 112.5%compared with the non-grouting pile and exhibit a positive correlation with the grouting volumes.The axial forces of the post-grouting pile is lower than the non-grouted pile within the depth of grouting returned and decreases with increasing grouting volume.When the pile top load is relatively low,the average side resistance of the post-grouting pile is slightly higher than that of the non-grouted pile and is little affected by the grouting volume within the depth of grouting returned.With the increase of the pile top load,the average side resistance of the post-grouting pile in the grouting returned depth is far higher than that of the non-grouted pile and increases with increasing grouting volume.For the same grouting pressure conditions,the different pile end post-grouting volumes mainly affect the average pile side resistance within the depth of grouting returned,whereas they have little effect on the height of grouting returned.The height of grouting returned is approximately 14 times the pile diameter above the pile tip.Moreover,the performance of the non-grouted pile shows the characteristics of the friction and end-bearing pile,and the post-grouting pile shows the characteristics of the end-support friction piles.The proportion of pile end resistance to pile top load for different grouting volumes piles decreases with the increasing of grouting volumes under the same pile top load.The improved mechanism of the post-grouting piles primarily involves the compaction and splitting of the grout on the pile tip and side soil according to the soil excavation analysis.