大直径深长钻孔灌注桩分层荷载传递特性试验研究

EXPERIMENTAL STUDY OF LOAD TRANSMISSION PROPERTY OF LARGE-DIAMETER BORED CAST-IN-SITU DEEP AND LONG PILE IN DIFFERENT SOIL LAYERS

基于常州高架一期工程现场静荷载和桩身应力测试结果,分析竖向荷载下大直径深长钻孔灌注桩在分层土中的荷载传递规律。由于试桩加载至破坏,故对此分析能为深入研究大直径深长钻孔灌注桩的承载性状提供有价值的工程参考。试验结果表明:大直径深长钻孔灌注桩端承力所占比例较低,荷载-沉降关系呈陡降型,存有明显拐点;侧、端阻力非同步发挥且相互影响,同时上下层侧阻力亦先后发挥至极限;通过对试桩的实测数据进行分析可得,埋深对桩周具有相似物理力学特征土层的侧阻力影响较大,一些土层实测侧阻力与勘察报告推荐值有很大差异;土层(1)和(3)荷载传递曲线属加工软化型,而桩端土荷载传递曲线属明显的双折线硬化模型,这说明上部土层有剪切破坏趋势,使侧阻产生一定程度削弱,而在承载时端承力有较大发挥空间。

The load transmission property of large-diameter bored cast-in-situ deep and long pile in different soil layers under vertical load is analyzed on the basis of measuring data of static load test and pile stress measurement in Changzhou viaduct road project I. The test pile is loaded to destruction, which can supply valuable project reference to further studying bearing capacity of larger-diameter bored cast-in-situ long pile. The study indicates that the bearing capability of pile bottom in deep soil layer accounts for lower proportion than skin friction; and the Q-s curves of large-diameter bored cast-in-situ long pile show steep drop type, especially with a significant inflection point. Skin friction and tip resistance of the pile have mutual influence on each other and don＇t display simultaneously： and the same situation also exists in side friction in soil layer, which demonstrates that the above soil layer first reaches the limit state： and then the lower soil layer. Burying depth has significant influence on side friction of soil layers around pile which has similar physical mechanical property and some values about side friction have great difference to recommendation value of the reconnaissance report according to measuring data. The load transmission curves of soil layer （1） and soil layer （3） correspond to process-softening model, and the load transmission curves of soil around pile bottom correspond to bilinear rigid model, which demonstrates that side friction of above soil layers is weakened to some degree for the soil layers have tendency to be destroyed by shearing： and a great deal of tip resistance of the pile is not displayed under vertical load.