膨胀土中基桩胀拔力原型试验研究

膨胀土含水率的变化直接影响基桩的工作性状，为研究实际工况条件下膨胀土中基桩的浸水胀拔特性，开展钻孔灌注桩在浸水条件下的胀拔力原型试验。试验结果表明，浸水过程中，土体位移缓慢增长，最后达到稳定，受土体密实度和含水率的影响，表层土体竖向膨胀位移总是大于深部土体位移；伴随着土体的吸水膨胀过程，桩顶胀拔力首先快速增大，之后缓慢增大，最终达到稳定。分析认为，桩顶胀拔力是浸水过程中土的胀切力、桩体自重和桩土界面摩擦力共同作用的结果，为保证建筑物的安全，应合理设置桩长，使中性点以下的桩体锚固力大于桩顶极限胀拔力。

Prototype experimental study of expansive force of pile embedded in expansive soil

The working pattern of single pile embedded in expansive soil will be influenced by the soil’s water content directly. In order to study how the soil influencing pile when it is soaking with water, the prototype test of expansive force of bored pile is carried out. The test result shows that the vertical displacement of soil increases slowly and to be stable finally. Influenced by soil water content and compactness, the vertical displacement of shallow area is always greater than that in depth. During the soil expansive process, the uplift force of pile top increases rapidly and then increases slowly; and at last to be stable. According to mechanical analysis of pile and test results, the expansive force is a comprehensive representation parameter of expansive shear force, pile weight and pile-soil interface friction. For more safety, pile length should be long enough to make sure the anchoring force of pile is larger than ultimate expansive force.