扩径桩抗压抗拔性能的颗粒流数值模拟

在地下水位以下较深的地下工程中，常采用扩径桩来承担结构今后受到的浮力．为了研究承担竖向受压荷载对抗拔桩今后承担上拔荷载的承载力的影响需要开展研究．采用二维颗粒流分析程序PFC2D对载荷试验中同一扩径桩先受压后抗拔进行了数值模拟分析．通过研究扩径桩在单纯承担上拔荷载和先受压、后受拔的过程中不同受荷阶段桩时步．位移曲线、桩土颗粒排列变化、颗粒位移的变化及荷载～沉降（上拔量）的对比分析，得出桩在下压和上拔到达极限荷载时的破坏性状，并与现场试验结果进行了对比．对先承担竖向受压然后抗拔的桩，与直接承担上拔的桩相比较，得知桩下压过程中桩周土体结构的破坏对桩随后的抗拔承载力有较大的影响．

Numerical Simulation of Particle Flow Code for Pile with Expanded Diameter under Compressive Load and Uplifting Load

Piles with expanded diameter are often used to resist the uplifting force of underground structure under water table. But the piles are subjected to compressive load during dewatering after excavation for foundation pit, which is usually the self-weight of underground structure. Since the piles are firstly compressed and then uplifted, the effect of compressive loading on the bearing capacity against uplifting needs to be investigated. In this study full scale loading tests were carried out. And based on the theory of particle flow code in 2 dimensions, a pile with expanded diameter that was firstly compressed and then uplifted in a loading test was studied through numerical simulation, and was compared with the results of actual pile loading tests. By using PFC2D, the time step-displacement curve, the change of particle position and the displacement of particles at different loading stages were also studied. And the load and displacement relations were obtained. The failure behavior of the piles subjected to uplift after compression and only uplift was investigated and compared. For the pile that was subjected to uplift after compression, its pullout bearing capacity was found to be affected significantly due to the breakage of structure of soil during the compressive loading process.