考虑加筋与遮帘效应计算群桩沉降的相互作用系数法

Interaction coefficients method for calculating piles group settlements considering reinforcing and restraining effect

群桩中各基桩在地基土中的加筋与遮帘效应是客观存在的,然而,在目前的桩基沉降理论与实践中,相关的研究仍显不足。基于剪切变形法理论,考虑桩的加筋与遮帘效应,求得各基桩在自身桩顶荷载作用下产生的沉降以及其引起相邻桩的附加沉降量,由此提出群桩中任两桩的相互作用系数简化公式,同时,也得到各基桩桩侧及桩端桩-土接触等效弹簧刚度,并基于荷载传递法原理,建立了成层地基条件下各基桩在自身桩顶荷载作用下的桩身位移平衡方程,推导出各土层层顶处桩身沉降、轴力与层底处桩身沉降、轴力之间的递推关系,进而将公式推广到高、低承台群桩基础计算中。工程算例分析表明,用该方法计算有较高的精度,求得的荷载-沉降曲线及两桩相互作用系数与实测值吻合较好;相互作用系数要明显小于弹性理论计算结果。

The reinforcing and restraining effect of piles embedded in soils is objective existence. However, the correlative research work on pile groups settlement methods is not deep enough and needs to be continued. Based on the shear displacement method, considering the reinforcing and restraining effect, the settlements of the analyzing pile caused by loads on the pile top were calculated, including the reduction effect caused by the existence of the other adjacent piles. And the additional settlements of the adjacent piles arising from the settlement of the loaded pile were obtained as well. Thus a simplified formula of interaction coefficients between any two piles was presented. Meanwhile, the equivalent shear stiffness coefficients of soil around each pile were developed; and an equation of displacements caused by load on top of the analyzing pile imbedded in multi-layered soils was built; so recurrence relations of settlement and axial force of pile shaft between upper and lower of each pile sections were respectively deduced; in the process of deduction, Boussinesq solution was modified to include the effect of different embedded depths, and then used to derive the equivalent stiffness coefficients of the soil under the pile tips. Lastly, the formula was extended to the settlements calculation of high and low cap pile groups. Different methods were compared with two engineering cases. The results show that the load-settlement curve computed by present method agreed well with those measured from real engineering cases; and the calculating interaction coefficients are much less than ones calculated by the elastic theory method.