沉箱-钢管桩逆作法复合基础试验

Experimental research on complex foundation of caisson-steel pile in top-down order

为研究逆作法复合基础的荷载与沉降关系、桩土荷载分担特性以及钢管桩受力性能,进行了单桩、沉箱及沉箱—钢管桩逆作法复合基础系列模型试验。结果表明:采用沉箱—钢管桩逆作法复合基础,先施工沉箱及部分上部结构,而后续进行钢管桩的压、封桩能充分利用土体的承载能力,压桩前土体与沉箱底板保持严密接触,上部结构荷载全部由地基土承担;压桩后,土体得到了加固,沉降减小,承载力提高;封桩后,继续增加的荷载主要由桩体承担,直至桩达到极限承载能力;由于沉箱的影响,使桩身上部轴力衰减平缓,桩侧摩阻力被削弱,同时使桩身中下部轴力衰减加剧,侧摩阻力发挥得到增强;6倍桩距时,可不考虑群桩效应对逆作法复合基础的影响。

Model tests on the single pile, caisson and complex foundation of the caisson-steel pile were designed to investigate the relation between the bearing capacity and the settlement, the load shear ratio between the soil and the pile, and the load carrying properties of the steel pile. The results indicate that the complex foundation in top-down order which constructes caisson and a part of superstructure firstly and then presses steel piles and scales the piles subsequently can take full advantage of the soil bearing capacity, that the caisson plate kept in close contact with the foundation soil which bear all of loads of the super- structure before pressing piles, that the foundation soil is strengthened after the pile pressed, the settlement of the foundation decreases and the bearing capacity enhances, that most of the incremental loads are supported by the pile until the pile reaches the ultimate bearing capacity, that the influence of the caisson makes the distribution of the axial force gently and the frictional resistance decreases at the upper part of the pile, meanwhile frictional resistance at the rest part increases, and that the pile group effect can be neglected if the pile spacing is 6 times of the pile diameter.