几种缺陷单桩竖向承载性状的现场模型试验研究

为评价灌注桩在施工过程中因形成缩径、扩径、断桩、泥皮等缺陷导致单桩竖向极限承载力变化的程度，针对缺陷桩单桩开展了现场模型试验研究。进行正常桩和缺陷桩的竖向静载模型试验，测试单桩竖向极限承载力，对比缺陷桩和正常桩的单桩承载特性，分析了缩径、扩径、断桩、泥皮等缺陷对单桩承载性状的影响。对比正常桩和缺陷桩的荷载-沉降关系曲线，得出了基于文中缺陷桩设计方案的结论，缩径缺陷和泥皮缺陷均使单桩竖向极限承载力降低，降幅在正常桩极限承载力的15%范围内；扩径缺陷桩的荷载-沉降关系曲线无明显陡降点，桩顶沉降较正常桩递增缓慢；断桩缺陷影响荷载-沉降关系曲线中反弯点的出现位置，即反弯点出现时的桩顶位移与断桩缺陷距地表的距离有关。

Field model test study of vertical bearing behavior ofsome kinds of single defect piles

To evaluate the changing degree of single pile vertical bearing behavior resulted by defect piles such as stem shrinkage pile, stem enlargement pile and broken pile which are developed in construction process, field model tests were used to analyze single defect piles. And measurements of its ultimate bearing behavior were carried out by conducting vertical static loaded tests of test piles with and without defects. Compared with normal piles, the influences of defects mentioned above on bearing behavior of piles were studied. Conclusions are drawn based on the designing scheme of test piles in the paper through comparative analyses of the load-settlement curves of normal piles and defect piles. Compared with the vertical ultimate load capacity of single normal pile, it reduces by less than 15 percent due to defects in single pile such as stem shrinkage pile or a pile with mud cake around. The steep drop point is not so clear in the load-settlement curve of single stem shrinkage pile, the top settlement of which increases more gradually than normal pile. The occurrence of inflection point in load-settlement curves of broken piles is determined by the distance of broken defect from ground surface.