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有限元数值模拟研究表明,基坑开挖土体回弹在扩底桩桩身引起较大的轴力,桩身的中性点位置靠近扩底端。在考虑基坑开挖影响时,桩身的真实轴力远较未考虑基坑开挖影响时大,且轴力的最大点并非在桩顶加载部位,在设计时应充分注意到这一特点给予桩身足够的配筋量。与轴力相应,在基坑开挖后,桩侧表面即存在较大的摩阻力;若忽略该部分摩阻力的存在,将导致对上拔荷载作用下桩侧摩阻力估计的较大偏差。承受上拔荷载后,扩底桩桩端阻力承担了37%左右各级荷载的增量,体现了扩底端在抗拔荷载作用下的有效性。
Finite element numerical simulation shows that the rebound of foundation excavation soil causes large axial force in the shaft of the expanded bottom piles, and the neutral point position of the pile body is close to the extended bottom end. When considering the influence of excavation, the true axial force of the pile body is much larger than that when the influence of excavation is not considered, and the maximum point of axial force is not at the top of the pile, which should be fully noticed in the design Give the pile enough reinforcement. Corresponding to the axial force, after the excavation of the foundation pit, there is a large frictional resistance on the side surface of the pile. Ignoring the frictional resistance of this part will result in a large deviation of the frictional resistance estimation of the pile under the action of the uplift load. After bearing the uplift load, the end resistance of the expanded bottom pile takes up about 37% of the incremental load at all levels, which reflects the effectiveness of the expanded bottom under the anti-pull load.