考虑异形效应Y形桩端阻力产生的附加应力研究

Y形桩作为一种新型反拱曲面异形桩，端阻力在桩身截面上具有不均匀分布的特性。虽将端阻力假定为均匀分布，与假定为集中力相比，附加应力计算结果更符合实际分布规律，但仍存在一定偏差。基于数值模拟结果，建立了Y形桩端阻力的不均匀分布模型，借助数学分析软件Mathematica的NIntegrate数值积分功能，以及Geddes推导应力解的思想，进而得出了考虑异形效应Y形桩桩端阻力作用在地基内部任意点竖向附加应力系数的数值计算方法。以主要影响因素外包圆半径R、模板弧度θ、开弧间距s、夹角弧度δ为变量，分别对比研究了将Y形桩端阻力假定为均匀分布和考虑异形效应的不均匀分布两种模式下附加应力的变化规律，并将考虑异形效应的端阻力产生附加应力计算方法用于沉降计算。对此现场静载荷试验数据表明，考虑异性效应的端阻力产生附加应力计算方法计算沉降与现场试验数据吻合度更高。

A study of the additional stress caused by the tip resistance of a Y-shape pile with considering abnormality effect

A Y-shape pile is a newly-developed abnormal pile with a reversed-arch surface. The tip resistance distribution along the pile bottom section is non-uniform. Although the calculated additional stresses, due to the assumed uniformly distributed tip resistance, is more close to the actual values compared to those due to the assumed concentrated tip resistance, the former still has some error. Based on the numerical simulation, the nonuniform distribution model of tip resistance for a Y-shape pile is developed, and used to calculate the additional stresses. By means of the integral function NIntegrate of Mathematica software and Geddes’s stress solution, the numerical calculation method is introduced to estimate the vertical additional stress coefficient at any point in foundation under the action of tip resistance of Y-shape pile with considering the effect of abnormality. Assuming the major factors as variables, including the outside circle radius R, template radian ?, open arc spacing s, and angle radian ?, the variation of additional stress is comparatively studied for two distribution patterns of tip resistance of the Y-section pile, i.e, the uniform distribution and the nonuniform distribution with considering abnormality effect, respectively, and the method for calculating the additional stress due to tip resistance is used for estimating the settlement with considering abnormality effect. Based on the field static load tests, it is found that the calculated settlements agree well with the measured results using the proposed method.