湿陷性黄土中成孔方式对桩基承载力影响试验研究

为了研究黄土地区成孔方式对桩基承载特性的影响，依托永寿至咸阳高速公路工程，对两个试验区4根试桩进行了静载试验，分析研究了不同成孔方式下桩基荷载传递规律。研究结果表明：成孔方式对桩基承载特性影响较大，黄土地区旋挖钻孔灌注桩承载力高于泥浆护壁循环钻孔灌注桩；循环钻孔灌注桩在成孔时需泥浆护壁，桩侧形成的泥皮会严重影响桩侧土体摩阻力的发挥，桩侧极限摩阻力值较小，桩端承担桩顶荷载比例较高；浸水后湿陷性黄土结构破坏，单桩承载力较原始状态有所下降；由于上覆黄土层湿陷量较小，浸水状态下桩侧土体并未产生负摩阻力。

An experimental study of influence of drilling method on the bearing capacity of pile foundation in collapsible loess area

To investigate the influence of drilling method on the bearing characteristics of pile foundation in loess areas, statically loading tests on four tested piles were carried out on two sites of the Yongshou-Xianyang Expressway project, and the loading transfer behavior of pile foundation with different drilling hole methods is analyzed. The experimental results show that the drilling method has significant influence on the bearing characteristics of pile foundation. The bearing capacity of bored pile by churning is much higher than that of circulation bored pile with slurry protection wall in loess area. The reason is that the borehole wall needs protecting during drilling, the formed mud cake significantly weakens the exertion of pile shaft resistance. This can result in a minor ultimate friction resistance and a larger tip resistance accounting for a larger percentage of the load on pile top. Loess structure is destroyed after immersion in water, so that the bearing capacity of pile decreases compared with the test pile in original state. Due to the fact that the collapse settlement of overlying loess is small, negative skin friction is not produced by the soils in immersion state at pile side