负摩阻力作用下透明土中管桩中性点位置模型试验

Experimental study on neutral point position of pipe pile embedded in Transparent sand under negative skin friction

中性点位置的确定是负摩阻力作用下桩基下拽力与下拽位移,以及整体桩基承载力设计与计算的最关键环节之一;已有规范给定的中性点位置确定经验方法往往与实际存在一定的出入。基于人工合成透明土材料,采用非插入式测试方法开展负摩阻力作用下管桩中性点位置测定模型试验,测得桩体和桩周土体的沉降规律,续而分析桩-土相对位移、确定中性点位置;为了对比分析,同时进行负摩阻力作用下不同直径管桩中性点位置测定的模型试验,对比分析其中性点位置与地面堆载等级的关系。试验结果表明,本文试验条件下,管桩的中性点位置位于0.7 H-0.9 H(H为桩长)范围内,略低于建筑桩基规范中给出的砂性土中基桩建议参考值(0.7 H-0.8 H);桩顶下拽位移近似随地面堆载等级呈线性增长。

The determination of neutral point position is one of the most important aspects in dragload,downdrag, and total bearing capacity of pile foundation design and calculation,in which pile foundation is influenced by negative skin friction.The empirical methods for determining neutral position specified by current design codes often result in values different than practical ones.Visual model tests on neutral point position of pipe pile under negative skin friction using non -intrusive testing methods were carried out on transparent soil.The displace-ments of pile and soil were measured,and the relative displacement of pile-soil and the position of neutral point were analyzed and discussed.In order to make a comparative analysis,model tests on pipe pile with different di-ameters under negative skin friction were also performed.The curves of neutral point position versus surcharge between pipe piles with different diameters were analyzed.The test results show that,in this model test condi-tion,the neutral point of pipe piles located approximately at 0.7 H -0.9 H (where H is the pile length),slight-ly lower than the values suggested by the Chinese Code (0.7 H -0.8 H ),and that the downdrag of pile is near-ly increases linearly with increasing surcharge load.