湿陷性黄土地区桥梁桩基工后沉降计算方法研究

Method for post-construction settlement of pile foundation of bridges in collapsible loess area

针对高速铁路工后沉降要求严格,湿陷性黄土地区桩基由于浸水引起的附加沉降计算研究不充分的现状,以现场大型桩基浸水试验结果为基础,分析了桩基浸水附加沉降的产生机理,提炼出湿陷性黄土地区高速铁路桥梁桩基工后沉降计算模型,提出了工后沉降计算方法。研究表明,浸水附加下沉是湿陷性黄土地区桥梁桩基需主要考虑的工后沉降,工后沉降可能比工前沉降大得多,桩身压缩沉降是沉降的主体,混凝土蠕变在沉降计算中不可忽略;通过荷载传递理论计算浸水前桩身轴力分布,假定浸水后桩侧阻力和桩端阻力同步发挥获得浸水后的桩身轴力分布,据此可分别计算构成工后沉降的桩身弹性压缩、桩身蠕变和桩端沉降。

With regard to the situation that the high-speed railway has requirements of strict post-construction settlement and the researches on the additional settlement of pile foundation caused by soils immersion are inadequate in collapsible loess area. Based on the field results of large pile immersion tests, the mechanism of the additional settlement of piles caused by soils immersion is studied, and a model is proposed. A method for calculating the post-construction settlement of pile foundation of bridges of high speed railway in collapsible loess area is put forward. The results show that the post-construction settlement of pile foundation of bridges should mainly consider the additional settlement caused by soil immersion in collapsible loess area, which mainly reflected by the compression of pile shaft and is much larger than the settlement only caused by structure load. The creep of concrete should not be neglected in the settlement calculation. The distribution of axial force of piles before soil immersion can be calculated using the load transfer theory, and that after soil immersion also can be obtained if assuming the pile side and pile end resistances develop synchronously. Thereafter, the elastic compression of pile shaft, creep deformation of concrete, and pile tip settlement, which contribute to the post-construction settlement, can be calculated separately.