Y型桩桩侧摩阻力产生附加应力的分析计算

Analysis and calculation of additional stress due to skin friction of Y-shaped vibro-pile

Geddes的应力解求解过程中将桩侧摩阻力简化为集中力,导致无法考虑桩径、桩长变化对桩侧摩阻力在地基内产生附加应力的影响,通过分析得出,对于长径比较小的短桩,由Geddes应力解计算的竖向应力系数与实际考虑桩径影响的结果相差甚远。通过首先在Y型截面上沿周边的9个积分区间线积分,然后再沿桩长进行积分的方式,借助数学分析软件Mathematica的NIntegrate数值积分功能,得出了Y型沉管灌注桩沿桩身矩形分布、沿桩周均匀分布侧摩阻力及沿桩身三角形分布、沿桩周均匀分布侧摩阻力作用在地基内部时任意点土中竖向应力分量的数值计算方法。分析了Y型截面4个独立变量外包圆半径R、模板弧度θ、开弧间距s、夹角度数δ对Y型桩侧摩阻力产生附加应力系数的影响及采用Geddes应力解计算产生的误差,并对桩长及计算深度对产生误差的影响也进行了分析,得到了一些有益结论。

Geddes stress solution is widely applied to settlement calculation of pile foundation. In order to find the solution, pile skin friction is simplified as concentrated force; however the influence of changing diameter and length of pile additional stress in the ground due to skin friction can not be taken into account. The actual calculated results of the short pile with low ratio of length to diameter are quite different from the results of vertical stress factor by Geddes stress solution. Using the numerical integral function of Nlntegrate in Mathematica software, a numerical method of calculating the vertical component of Y-shaped pile skin friction acting at any point in the ground is obtained. One loading case of the skin friction is rectangular distribution from top to bottom along the pile body and uniform distribution in circumference; the other one is triangular distribution from top to bottom along the pile body and uniform distribution in circumference of Y-shaped section. The influences of four independent variables R, θ, s, δ, of Y-shaped section on additional stress factor due to skin friction and errors produced by Geddes stress solution are analysed; and the influences of pile length and calculating depth on errors are also analysed. Some significant conclusions are obtained.