循环荷载下粉煤灰复合地基竖向承载特性模型试验研究

为研究粉煤灰单桩复合地基竖向循环承载特性,开展在循环荷载作用下的室内模型试验。通过监测桩身及土体变化情况,分别从桩顶累计沉降、土压力、桩身内力等方面进行分析。试验结果表明：循环桩顶累计沉降前期呈现快速增长,而循环荷载比临界值为0.6,将后期沉降变化划分为稳定型和增长型两种趋势;桩侧土压力主要影响桩身上半部分土体,并沿竖向和径向均出现衰减现象,且竖向衰减更为明显;对桩端阻力强化系数Z和桩侧阻力弱化系数D分别进行拟合,可得到对实际工程中不同循环周期下桩端、桩侧阻力强弱变化情况分析,具有参考依据的函数方程;循环荷载下的桩端/桩侧荷载分担比呈现动态变化,循环周期的增加,将会存在桩端所占承载比例超越桩侧所占比例的占比反超点,循环幅值越大,出现反超点所需的循环次数也越少。

Experimental study on vertical bearing characteristics of fly ash composite foundation under cyclic loading

In order to study the vertical cyclic load bearing characteristics of fly ash single-pile composite foundation, laboratory model tests under cyclic load were carried out. By monitoring the changes of pile body and soil, the accumulative settlement of pile top, soil pressure and internal force of pile body are analyzed respectively. The test results show that the accumulative settlement of cyclic pile top presents a rapid increase in the early stage, and the critical value of cyclic load ratio M=0.6. The settlement changes in the later stage are divided into two trends: stability and growth. The soil pressure on the side of the pile mainly affects the soil on the side of the pile, and decreases along both vertical and radial directions, and the vertical attenuation is more obvious. By fitting the strengthening coefficient Z of pile tip resistance and the weakening coefficient D of pile side resistance, a functional equation with reference can be obtained to analyze the changes in the strength of pile tip and pile side resistance under different cycles in actual engineering. The load sharing ratio of pile end/pile side under cyclic load presents a dynamic change. With the increase of cycle period, there will be a reverse overload point in which the load proportion of pile end exceeds the proportion of pile side. The larger the cycle amplitude, the fewer cycles required for the reverse overload point.