基于极限平衡法的现浇X形桩群桩负摩阻力计算分析

软弱土及湿陷性黄土等地区桩基负摩阻力计算是桩基础设计与施工必须考虑的问题之一，目前针对群桩负摩阻力计算方面的研究相对较少。采用有效应力法计算单桩负摩阻力，基于极限平衡原理计算负摩阻力群桩效应系数，从而得到群桩负摩阻力计算公式。结合现场试验结果，对现浇X形桩群桩负摩阻力及桩身下拽力进行计算分析，并讨论了群桩基础中各基桩位置对桩身下拽力的影响，以及群桩效应系数随相关影响因素的变化规律。研究结果表明，文中计算结果与现场实测结果具有良好的一致性；地面堆载等级越高，群桩所受的桩身下拽力越大，且群桩效应系数随着桩间距的增大而增大，随着负摩阻力系数和中性点深度比的增大而减小。

Analysis of negative skin friction calculation of X-section cast-in-place pile groups

Calculation of negative skin friction on piles in areas of soft soil and collapsible loess is one of the issues must be considered in pile foundation design and construction;while studies on the calculation of negative skin friction on pile groups are relatively little at present.Effective stress formula,negative skin friction on single pile is calculated.Based on limit equilibrium theory,the calculation method of the pile group effect coefficient under negative skin friction is obtained.With field test results,negative skin friction and drag-load on X-section cast-in-place pile groups are analyzed.The influence of location of piles in pile foundation on drag-load along pile shaft is discussed;and the change rule of the group effect coefficient varies with different influencing factors.The results of calculation and field measured results are in good agreement;the greater the surface load is,the greater the drag-load on pile groups is,and the pile group effect coefficient increases with pile spacing increase and it decreases with the increase of negative skin friction coefficient and the depth ratio of neutral point.