黄土洞穴对桥梁桩基竖向承载特性影响的离心模型试验
Centrifuge model test on effect of underground loess cave on vertical bearing characteristic of bridge pile foundation

为给黄土地下洞穴区域的桥梁桩基在设计计算方法和施工技术等方面研究提供依据，针对实际桥梁桩基遇到黄土地下洞穴时，往往盲目地对洞穴先处理再施工，既无法保证桩基安全，也不够经济合理等问题，基于铝管模拟桩体、可发性聚乙烯（expandable polystyrene, EPE）塑料泡沫模拟黄土地下洞穴的离心模型试验，开展了黄土地下洞穴对桥梁桩基竖向承载特性的影响研究，分析了竖向荷载作用下桩与洞穴水平间距、洞穴发育深度及桩底与洞穴垂直间距等因素对桥梁桩基竖向承载力、桩身轴力和桩侧摩阻力的影响。研究结果表明：洞穴发育深度小于20 m且桩与洞穴水平间距大于1.0倍桩径，桩与洞穴水平间距大于桩径的20%且洞穴发育深度小于5 m，洞穴距桩底超过8 m时，桩基竖向极限承载力受洞穴的影响均较小；随着桩与洞穴水平间距的增大，桩基竖向极限承载力逐渐提高，水平间距越小，桩侧摩阻力越小，桩身轴力有所增大；随着桩底与洞穴垂直间距的逐渐增大，桩基竖向极限承载力逐渐增大，垂直间距越小，桩侧摩阻力发挥越完全，桩身轴力衰减越快；相同荷载作用下，桩与洞穴水平间距越小，洞穴发育深度越深，桩侧摩阻力越小；桩顶荷载较小时，桩底与洞穴垂直间距越小，桩侧摩阻力越大。研究成果可为黄土地下洞穴区域桥梁桩基础的设计提供技术依据。
Due to the lack of enough reference on design calculation method and construction technology of bridge pile foundation in loess region with underground caves, loess caves are blindly treated before construction on the condition of bridge pile foundation with loess underground caves, which can not guarantee the security of pile and is also uneconomical. According to the centrifugal model test with Aluminum tube simulating pile and expandable polystyrene (EPE) plastic foam simulating loess cave, the influence of loess underground caves on vertical bearing characteristic of bridge pile foundation was studied. Under the action of vertical load, the effect of some factors on vertical bearing capacity of bridge pile foundation, axial force of pile shaft and pile side friction resistance were analyzed. These factors include the horizontal spacing between pile and cave, the depth of cave development and the vertical spacing between pile bottom and cave. The results show that when the depth of cave development is less than 20 m and the horizontal spacing between pile and cave is larger than 1.0 times of the pile diameter, or the horizontal spacing of pile and cave is larger than 20% of pile diameter and the depth of cave development is less than 5 m, or the vertical spacing between pile bottom and cave exceeds 8 m, the vertical ultimate bearing capacity is less affected by the cave. With the increase of horizontal spacing between pile and cave, the vertical ultimate bearing capacity of pile foundation is gradually increased. The smaller the horizontal spacing, the smaller the pile side friction resistance and the larger the axial force of pile shaft. With the gradual increase of vertical spacing between pile bottom and cave, the vertical ultimate bearing capacity of pile foundation also increases. The smaller the vertical spacing, the bigger the pile side friction resistance, and the smaller the axial force of pile shaft. Under the same load, the smaller the horizontal spacing between pile and cave, the deeper the