循环荷载下圆柱形桩与楔形桩复合地基工作性状对比试验研究

为探讨循环荷载作用下夯实水泥土圆柱形桩与夯实水泥土楔形桩复合地基工作性状的差异，通过室内模型试验，并在桩顶及桩周土表面埋设微型土压力盒，进行循环荷载下夯实水泥土圆柱形桩和楔形桩的4桩复合地基及单纯软土地基工作性状对比试验，探讨循环应力比和加载周数对夯实水泥土圆柱形桩和楔形桩复合地基永久沉降、桩-土应力比的影响规律。研究软土地基加固方法对永久沉降和桩-土应力比的影响，揭示了循环应力比与桩-土应力比的关系。研究结果表明：采用夯实水泥土桩加固软土地基，能提高地基的临界循环应力比，增强地基抵抗循环荷载的能力；在相同的加荷周数和循环应力比的加载条件下，采用夯实水泥土楔形桩加固软土地基对降低地基永久沉降的效果比采用夯实水泥土圆柱形桩的效果要好，且楔形桩的楔角越大，降低永久沉降的效果越明显。循环应力比越大，桩-土应力比越大；桩-土应力比随楔形桩楔角的增大而增大，随加载周数的增加而降低，并存在一临界加载周数；当加载周数小于临界周数时，桩-土应力比随加载周数迅速降低；当加载周数超过临界周数时，桩-土应力比几乎不随加载周数的变化而变化。

Comparison experimental research on work behavior of composite foundation with column and tapered piles under cyclic loadings

To study difference for the work behavior of the composite foundation with rammed cement-soil column and tapered piles under cyclic load, based on the indoor model tests, and installing the miniature soil pressure boxes on the pile-top and the soil surface, the contrast model tests of working properties for the composite foundation with 4 rammed cement-soil column piles and with 4 rammed cement-soil tapered piles, and the soft foundation are performed in laboratory, respectively. The influence laws of the cyclic stress ratio and the number of cyclic load on the permanent settlement and the pile-soil stress ratio of the composite foundation with rammed cement-soil column and tapered piles are explored. The influence of the reinforcing methods on the permanent settlement and the pile-soil stress ratio are researched in the soft foundation. The relation of the cyclic stress ratio and the pile-soil stress ratio is revealed. The results of the study show that the critical cyclic stress ratio and the ability to resist cyclic load of the foundation may be enhanced by the composite foundation with rammed cement-soil piles. In the same loading conditions for the same number of cyclic load and the same cyclic stress ratio, the effect that the permanent settlement is decreased by the composite foundation with rammed cement-soil tapered piles is better than that by rammed cement-soil column piles. The greater the wedge angle is, the better the effect is. The greater the cyclic stress ratio is, the greater the pile-soil stress ratio is. The pile-soil stress ratio increases as the wedge angle of the tapered pile increasing; but that decreases as the number of cyclic load increasing. There is a critical number of cyclic load. When the number of loading cycle is less than the critical number of cyclic load, the pile-soil stress ratio decreases rapidly as the number of cyclic load increasing. When the number of loading cycle is more than the critical number of cyclic load, the pile-soil stress ratio almost has no change as the number of cyclic load increasing.