关键词: 永久沉降, 复合地基, 桩-土应力比, 循环应力比

Abstract: 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.

Key words: permanent settlement, composite foundation, pile-soil stress ratio, cyclic stress ratio