高液限膨胀性黏土基桩工作性状的离心机试验研究

Centrifuge modelling of working performance of foundation pile embedded in expansive clay with high liquid limit

通过离心机试验研究高液限强膨胀性黑棉土地基中4根模型基桩在浸水条件下桩头位移和桩身轴力的变化规律,考虑的影响因素包括桩长、桩头荷载以及是否采用隔胀措施。通过自主设计制作的离心机内降雨装置和模型土层中的渗流通道实现黑棉土地基浸水条件。试验发现,黑棉土浸水后对桩身轴力的影响分为两阶段:前期土体刚度降低阶段,黑棉土遇水刚度降低后能提供的摩阻力明显降低,使得桩身轴力增大;后期胀拔阶段:黑棉土遇水膨胀隆起,对桩基产生向上的胀拔力,桩身轴力减小。此外,浸水引起的桩头位移变化与桩顶受荷情况密切相关:未受荷桩发生上拔位移,而荷载为625 k N的桩发生沉降位移。在桩周采取隔胀措施可以削弱甚至消除黑棉土变形对桩基的不利影响。

The centrifuge tests are carried out to study the change of displacements of pile head and axial forces of four single piles embedded in strong expansive black cotton soil with high liquid limit after being submerged considering the influences of pile length, pile head load and expansion isolation measures. The self-developed rainfall facility in the centrifuge and the artificial seepage path in the model stratum control the submerging condition of the black cotton soil foundation. It is found that the effects of rainfall condition on the axial forces of piles can be divided into two phases. In the first softening phase, the wetted expansive soil provides less friction resistance, which increases the axial forces of piles. And in the second expansion draft phase, the swelling uplift of expansive soil produces more friction resistance and the axial forces of piles decrease. In addition, the displacement of pile head caused by the submerging is closely related to its load. Under rainfall conditions, the pile without load is uplifted, while the pile with load of 625 k N settles. Taking expansion isolation measures around the pile body will decrease or even eliminate the negative effects of expansive soil deformation on pile foundations.