沉箱-钢管桩逆作法复合基础试验

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.

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

Model test s on the sing le pile, caisson and complex foundat io n o f the caisson-steel pile w ere designedto invest igate the relat ion betw een the bearing capacity and the set tlement , the load shear ratio between the soil and the pile, and the lo ad car rying proper ties of the steel pile. The result s indicate that thecomplex fo undat ion in top-dow n order w hich const ructes caisson and a par t of superst ructure first ly andthen presses steel piles and seales the piles subsequent ly can take full adv antage of the soil bearing capacity, that the caisson plate kept in clo se contact w ith the foundation soil w hich bear al l of loads of the superstructure befor e pressing piles, that the foundat io n so il is st reng thened af ter the pile pressed, the set tlementof the foundat io n decreases and the bearing capacity enhances, that most of the incremental loads aresupported by the pile unt il the pile reaches the ult imate bearing capacity , that the inf luence o f the caisso nmakes the dist ribut ion of the ax ial force gently and the frictio nal resistance decreases at the upper part ofthe pile, meanwhile fr ict ional r esistance at the rest part increases, and that the pile g roup ef fect can be neglectedif the pile spacing is 6 t imes of the pile diameter.