自重湿陷性黄土与单桩负摩阻力离心模型试验

 为研究和分析黄土的湿陷变形性质与桩基的负摩阻力，采用离心模型试验的方法分别对原状自重湿陷性黄土与重塑湿陷性黄土进行模拟浸水试验。试验研究结果表明：原状和重塑湿陷性黄土浸水湿陷过程主要分为3个阶段，即显著湿陷变形阶段、湿陷稳定变形阶段以及水位下降后土体的固结变形阶段。根据试验结果，对于以沉降观测为目的的试验研究中，用重塑黄土代替原状黄土进行离心模型试验模拟其湿陷变形的方法是可行的。进而分析基桩负摩阻力分布规律及中性点位置的变化规律。单桩的负摩阻力分布及中性点位置是一动态变化过程，中性点位置与桩长的比例为0.68～0.82。

CENTRIFUGAL MODEL TESTS ON SELF-WEIGHT COLLAPSIBLE LOESS AND NEGATIVE SKIN FRICTION OF PILE FOUNDATIONS

Collapse settlement，collapsibility of self-weight collapsible loess and negative skin friction of pile foundation are crucial issues in the basic research of collapsible loess ground. The centrifugal model test is used to simulate the immersion test with undisturbed and remolded collapsible loess foundations，to research and analyze the collapsibility of loess and negative skin friction of pile foundations. The research results show that the processing of undisturbed and remolded loess collapsibilities can mainly be divided into three stages，which are the stages of significant of collapsible deformation，stabilization stage of collapsible deformation and soil consolidation deformation stage after the dropping of water level. The method of centrifugal model test which uses remolded collapsible loess instead of undisturbed collapsible loess to research the self-weight loess collapsibility is practicable for the purpose of settlement study by analyzing the test data. Then the changing laws of negative skin friction and the position of neutral point are concluded. The movement of negative skin friction and the position of neutral point are a continuous changing process. The ratio of the neutral point position to length of pile is in the ranges of 0.68–0.82.