超深开挖对抗拔桩承载力影响的离心机试验研究

Effects of deep excavation on uplift capacity of piles by centrifuge tests

深基坑开挖会改变桩周土的应力状态,影响抗拔桩的承载力。通过离心机模型试验,研究了超深开挖对抗拔桩承载力的影响。采用考虑基底土超固结效应影响的有限元数值模拟分析方法,对离心机试验进行了计算分析,研究超深开挖对抗拔桩承载力影响的内在机理。研究结果表明:坑内土体卸荷,桩侧土体有效应力降低,抗拔桩承载力下降;受基底土超固结效应的影响,桩侧土静止土压力系数要大于正常固结状态,桩侧极限摩阻力与抗拔桩承载力大于正常固结状态;不考虑基坑开挖对桩周土应力水平的影响,以覆土条件下的承载力做为设计取值,偏于不安全;考虑基坑开挖对桩周土应力水平的影响,但不考虑基底土的超固结特性,抗拔桩承载力的取值偏于保守。

The stress state of the soil around piles and the bearing capacity of uplift piles will be changed by deep excavation. Through centrifuge tests, the effects of ultra-deep excavation on the bearing capacity of uplift piles are analyzed. Using the finite element numerical simulation analysis method which takes the effects of over consolidation into account, the centrifuge tests are calculated, and the mechanism of the effects of ultra-deep excavation on bearing characteristics of uplift piles is analyzed. The results show that under the influence of over consolidation of base soil, the coefficient of earth pressure, the pile-side ultimate friction resistance and the bearing capacity of uplift piles are larger than those under normal consolidation. If the effects of pit excavation on stress level of soil are not considered, it will be unsafe to take the bearing capacity as design value. If the effects of pit excavation on stress level of the soil around piles are taken into account, while the capacity of over consolidation is not considered, the bearing capacity of uplift piles will be underestimated.