阶梯型变截面管桩沉桩阻力计算方法与模型试验研究

RESEARCH ON METHOD FOR PENETRATION RESISTANCE AND MODEL TEST OF STEP SHAPED CROSS-SECTION PIPE PILE

基于Vesic圆孔扩张理论,考虑初始应力对极限扩孔压力的影响,得到考虑深度影响的极限扩孔压力求解式,并以此建立变截面管桩桩端与变截面处端阻力的表达式。通过考虑阶梯型变截面管桩变截面处端阻力反力对下部桩侧摩阻力的影响,得到了变截面管桩沉桩过程中侧摩阻力的计算式,并与端阻力叠加建立变截面管桩沉桩阻力理论算式。为验证算式的可行性,对等截面与变截面管桩进行了室内模型试验,将试验结果与计算结果进行对比分析,结果表明:变截面管桩沉桩阻力曲线与等截面管桩有较大的差异,在变截面位置前、后,沉桩阻力出现明显的突变。将变截面管桩同平均直径相等的等截面管桩对比发现,变截面位置之前,变截面管桩端阻力和侧摩阻力均低于等截面管桩,而变截面位置之后,端阻力与侧摩阻力反而高于等截面管桩,表明变截面管桩比等截面管桩更能够发挥桩身的承载潜能。此外,计算值较好地反映了变截面管桩沉桩阻力与入土深度的关系,且与实测值拟合度较高。

Based on Vesic cavity expansion theory and initial stress of cavity expansion of different depth in soil,the formula for limit expansion pressure was proposed,and then a calculation method for resistances on pipe tip and position of step shaped cross-section was established. Furthermore,by thinking about effect of the reaction at the tip of the step shaped cross-section pipepile on sliding friction of lower pile,a calculation formula for sliding friction of step shaped cross-section pipe pile was deduced. Finally,the penetration resistance of step shaped cross-section pipe pile could be composed by resistances on pipe tip and sliding friction around step shaped cross-section pipe pile. To verify the feasibility of theory method in the paper,model tests for penetration of uniform section pipe pile and step shaped cross-section pipe pile were carried out in lab,and then a comparative analysis was done between results by test and theory formula. The results showed that curves of penetration resistance had a great difference between step shaped cross-section pipe pile and uniform crosssection pipe pile. The curves of step shaped cross-section pipe pile existed a sudden change on the position of shaped crosssection. Compared with uniform cross-section pipe pile of same average diameter,it was found that the resistances on pipe tip,position of variable cross-section and sliding friction around pipe pile were lower than uniform cross-section pipe pile before the position of shaped cross-section,and the resistances on pipe tip and position of shaped cross-section were higher than uniform cross-section pipe pile after the positon of step shaped cross-section. The calculation results could reflect the relationship between penetration resistance and pile legth in soil,which were very closed to the results of test.