基于总应力法的静压桩极限承载力时效性研究

考虑天然饱和黏土的应力历史和初始应力各向异性,推导得出了静压沉桩过程和再固结过程中静压桩周土体应力状态的变化规律。在此基础上,根据静压桩承载时桩侧土体应力状态与单剪试验及三轴试验中土体应力状态之间的相关性,基于总应力法推导了天然饱和黏土地层中静压桩时变承载力的解析解,提出了桩侧和桩端承载系数的理论计算方法。采用离心模型试验对本文解答进行验证,研究了沉桩结束后静压桩承载力随再固结时间的变化规律,分析了土体原位力学特性与静压桩承载系数之间的关系。研究结果表明,沉桩结束后静压桩承载力的增长主要是由于桩侧承载力的增长,而且静压桩承载力在沉桩结束后较短时间内增加的幅度较大,随后增长幅度变缓并趋于稳定;土体超固结比和静止侧压力系数越大,沉桩结束后承载力增长速率越快,但桩侧和桩端承载系数均随土体超固结比和静止侧压力系数的增大而减小。

Time-dependent ultimate bearing capacity of jacked pile based on total stress method

Considering the stress history and the initial stress anisotropy of natural clay, the stress variation of the soil around the pile during the pile installation process and the reconsolidation phase is derived. Then, according to the relationship among the stress states of the soil near the pile during pile loading and the stress variation of the soil in the simple shear and triaxial tests, an analytical solution to the time-dependent ultimate bearing capacity of the jacked pile is derived based on the total stress method. A theoretical method for calculating the bearing capacity factor of pile shaft and tip is proposed. The theoretical solution is verified by the centrifuge tests, and the variation of the bearing capacity with reconsolidation time is studied. The relationship between the bearing capacity factor and the in-situ mechanical properties of the natural clay is also analyzed based on the theoretical solution. The results show that the increase of the bearing capacity of the jacked pile after installation mainly stems from the increase of the bearing capacity of pile shaft. The bearing capacity increases rapidly in short time after the pile installation. Then, the change of bearing capacity is insignificant and tends to a stable value. The larger the overconsolidated ratio and the lateral pressure coefficient, the faster the increase of bearing capacity. However, the bearing capacity factors of pile shaft and tip decrease with the increase of the overconsolidated ratio and the lateral pressure coefficient.