浅薄层湿陷性黄土场地单桩承载特性试验

为了分析浅薄层湿陷性黄土场地荷载对桩基的影响规律，设计了单桩未浸水和浸水加载试验。结果表明:浸水后黄土湿陷对桩体产生了负摩阻力，在桩顶荷载条件下使桩体沉降，桩身轴力及桩侧摩阻力均发生了显著变化。较未浸水工况，浸水后的桩体沉降量明显增大，当接近设计极限荷载时，桩体的沉降量发生突变，残余沉降量增大。浸水后桩体的轴力最大值位置由桩顶转换至桩顶下湿陷性黄土层，且轴力的峰值大于桩顶的荷载，桩体中上部位置轴力普遍增大，轴力最大值位置与中性点位置相对应，浸水后桩侧摩阻力体现出双峰特征。由此可见，湿陷性黄土场地浸水后的荷载对桩体的变形和受力均有较大影响，应在桩体的设计中综合考虑安全和经济因素来对荷载进行取值。 

Bearing capacity of single pile in some sites with shallow thin layer of collapsible loess

To understand the impact of loading force on the performance of piles in a shallow thin layer of collapsible loess, the authors carried out non-flooded test and immersion test using a filling pile. The results reveal that when the soil is submerged, the collapse of the soil results in a negative friction along the pile. In addition, the pile settlement, axial force of pile and lateral friction on the pile changed significantly. Compared with the performance of the pile in soil under natural water content, when the pile was installed in submerged loess, the pile settlement increased significantly. When the ultimate designed load was applied, the increase rate of pile settlement changed resulting in an increase of residual settlement. The location of maximum axial force was observed at the base of the pile located in the collapsed loess, rather than at the top of the pile in the soil under natural water content. In addition, the observed maximum axial force was larger than the loading force. Also, the axial force above the middle section of the pile in the submerged soil was overall larger than that in the soil under natural water content. The location of the maximum axial force coincides with the location of the neutral point of the pile. The authors also observed two peak values of the lateral friction along the pile in the submerged soil. It can be concluded that the deformation and settlement of a pile in submerged loess soil varies a lot compared with that in the soil under natural water content. Therefore, it was suggested that these differences resulting from the collapse of the loess should be taken into account in the pile design.