考虑堆载和桩载施加顺序的单桩负摩阻力模型试验研究

Model tests on negative skin friction of single pile considering applying sequence of pile load and surcharge loading

通过室内模型试验,研究堆载和桩载施加顺序对单桩负摩阻力的影响。试验结果表明:先堆载后桩载工况下,堆载完成后,中性点位置离桩顶最远,随桩载增加,中性点位置逐渐上移,最终中性点位置在桩顶以下0.5l附近,桩身轴力呈先增加后减小的趋势,单桩承载力发挥系数为0.69。先桩载后堆载工况下,先施加桩载时,桩身轴力沿深度逐渐减小,无中性点,施加堆载时,轴力呈先增加后减小趋势,中性点出现并逐渐下移,最终中性点位置在0.41l附近,单桩承载力发挥系数为0.86。先桩载后堆载较先堆载后桩载桩基承载力发挥系数大,即桩基承载力安全储备小。以上分析表明,荷载施加顺序对基桩的负摩阻力分布有很大的影响,建议在实际工程中综合分析地质条件、桩基的受力特点及承载要求,选取合适的加载顺序来减小桩身负摩阻力。

Based on the laboratory model tests, the influence of the sequence of pile load and the soil load surrounding the pile on the negative friction of single pile is studied. The results show that under pile-soil load, after the applying of the soil load surrounding the pile, the neutral point is the furthest away from pile top. With the increase of pile load, the position of the neutral point gradually moves up, eventually, 0.5 l far from the pile top. The axial force of pile body increases first and then decreases, the exert coefficient of bearing capacity of single pile is 0.69. When the pile load is first applied, the axial force of pile shaft gradually decreases along the depth, there is no neutral point. While the soil load is applied, the axial force increases first and then decreases, and the neutral point appears and gradually moves down, finally it is near 0.41 l, and the exert coefficient of bearing capacity of single pile is 0.86. There is the greater exert coefficient of bearing capacity in the pile-soil load sequence, that is, the safety reserve of the bearing capacity of the pile is smaller. The above analysis shows that the bearing layer of the pile tip and the sequence of loading have great influence on the distribution of negative skin friction. It is suggested to select the appropriate loading sequence to reduce the negative skin friction of the pile by analyzing the geological conditions, stress characteristics of the pile foundation and bearing requirements in practical engineering.