竖向荷载下膨胀土桩基承载室内模型试验

利用自主研发的多向桩基加载系统,开展了室内模型试验,研究了膨胀土中桩基分别在最优含水率和饱和含水率条件下的下压和上拔荷载桩基的承载特性。试验结果表明:膨胀土含水率的变化,对抗压桩的极限承载力影响更为明显,对抗拔桩的极限位移影响更为明显。随着含水率的增加,尽管抗压桩和上拔桩的极限侧摩阻力均减小,且减小程度接近,但上拔荷载作用下极限侧摩阻力明显低于下压荷载的极限侧摩阻力。不同含水率条件下,抗压试验桩身极限侧摩阻力呈抛物线形分布,而上拔试验桩身极限侧摩阻力呈线性分布,含水率的增加使抗压桩和上拔桩的极限承载力显著减小,且抗压桩减小幅度更大,但抗压桩的极限承载力始终大于上拔桩的极限承载力。

Model tests on bearing characteristics of pile foundation in expansive soil foundation under vertical loadings

Based on the self-developed multi-directional load system for piles a series of model tests are carried out to study the behaviors of compressive and uplift loaded piles in expansive soils with two states of optimal water content and full saturation. The test results show that the change of water content of expansive soils has more significant influences on the behaviors of compression piles than those of tension piles, but more considerable on the deformation of tension piles. The ultimate bearing capacity of compression piles are always greater than that of tension piles. With the increase of water content, the ultimate skin frictions of compression piles and tension piles both decrease, but the ultimate skin friction under uplift load is obviously smaller than that under downward compressive load. Under different water contents, the ultimate skin friction of compressive piles is parabolically distributed, while that of uplift piles is linearly distributed. This is due to the fact that the displacement of the top of the tension piles is larger than that of the compression piles when the pressure piles and the uplift piles reach the ultimate bearing capacity, which makes the deep side friction of the tension piles play more fully. With the increase of water content, the ultimate bearing capacities of compression piles and tension piles decrease significantly, and the decrease of compression piles are even greater, but the ultimate bearing capacity of compression piles are always larger than that of tension piles.