循环荷载下混凝土单桩-冻土流变效应试验

Experiment on Concrete Single Pile-frozen Soil Rheological Effect Under Cyclic Loading

为明确冻土地区混凝土桩基在循环荷载作用下桩土流变效应对桩端位移、桩端阻力以及桩侧冻结应力的影响,利用在冻土中的混凝土模型桩顶端施加正弦波循环荷载的方法,包括改变循环荷载大小、加载频率和冻土温度,开展了循环荷载下桩土流变效应的研究。结果表明:循环荷载大小、荷载频率及冻土温度是影响混凝土单桩-冻土流变效应的主要因素;冻土流变效应的存在,致使桩侧冻结应力随时间推移而降低,而桩端阻力逐渐变大;荷载频率增大,桩侧冻结应力也随之变大,而趋于稳定的时间较短;温度升高,桩端位移就越大,桩侧冻结应力越小,其趋于稳定所需时间也较长;对于多年冻土区桩基础,在设计及运营中应尽量保持及降低冻土的负温,降低荷载频率。

In order to clarify the pile-soil rheological effect of concrete pile foundation in permafrost areas under cyclic loading on the pile end displacement, the pile end resistance, and the pile side freezing stress, a research on pile-soil rheological effect under cyclic loading was carried out by applying the method of the sine wave cyclic loading exerted on the top of concrete model in frozen soil, including the change of cyclic loading size, loading frequency and the temperature of frozen soil. The results show that cyclic loading size, loading frequency and the temperature of frozen soil are the main factors affecting the concrete pile-soil rheological effect. Due to the existence of rheological effect of frozen soil, the pile side freezing stress decreases while the pile end resistance increases gradually with the passage of time. At the same time, the pile side freezing stress increases with the increase of loading frequency, but the time of stability is relative short. When the temperature rises, the pile end displacement becomes larger, while the pile side freezing stress becomes smaller, and the time of stability becomes longer. For the pile foundation in permafrost areas, the negative temperature of frozen soil should try to be kept and decreased, and the loading frequency be reduced in the process of design and operation.