两种饱和土中桩基侧向动力响应特性试验研究

Experimental study of lateral dynamic response characteristics of pile foundation in two kinds of saturated sands

自从2008年汶川地震以来,对于饱和砂砾土液化问题的研究一直是岩土工程界与地震工程领域关注的热点。本文基于振动台试验,通过输入不同的台面波形,对饱和砂土和砂砾土侧向动力响应特性进行对比分析研究。以试验成果为基础,对桩基在饱和砂土与砂砾土两种不同液化土中侧向动力响应特性的异同也进行了初步探讨。研究结果表明:饱和砂砾土具有与饱和砂土类似的液化现象和特点,随着振动输入,饱和砂土孔压先逐渐升高然后又逐渐降低至低水平,而饱和砂砾土在初期迅速升高,而随后的残余孔压没有明显减低并一直保持较高水平至振动结束;饱和砂土土表加速度衰减速度要明显快于饱和砂砾土,在降低时刻上饱和砂砾土明显滞后于饱和砂土,说明饱和砂砾土较饱和砂土具有较强的抗液化能力;正弦波输入下饱和砂土中承台加速度随着孔压升高先增大后减小然后又缓慢升高,而饱和砂砾土中承台加速度仅经历了先升后降的简单过程,饱和砂土中桩头加速度在振动初期的放大倍数要低于砂砾土,而在振动输入后期,饱和砂土桩头加速度要比饱和砂砾土中放大效果明显,承台位移响应时程则表现出极为相似的规律,地震波输入下的反应与正弦波略有不同。

Since the 2008 Wenchuan earthquake, the study of liquefaction of saturated gravel soil was always concerned in the geotechnieal engineering field and the earthquake engineering field. Based on the shaking table test and different shaking table waveforms input, the lateral dynamic response characteristics of saturated sand and gravel soil were analyzed and compared. With the basis of the above experimental results, the differences and similarities of lateral dynamic response characteristics of the pile in the saturated sand and gravel soil were preliminary explored. The research results show that the liquefiable phenomena and characteristics of pile in the saturated gravel soil are analogous to the saturated sand. With the vibration input, the pore pressure of saturated sand increases gradually at first, and then gradually reduces to a low level, while that of the saturated gravel soil increases rapidly in the early, and the subsequent residual pore water pressure do not significantly reduce and maintains a high level with the vibration ending. The acceleration of soil surface in saturated sand decays much faster than that in the gravel soil, and the reducing time of gravel soil lags behind the sand, so it shows that saturated gravel soil has a stronger anti-liquefaction capacity than the saturated sand. With the sine wave input, the cap acceleration in the saturated sand increases at first, and then decreases, and increases slowly finally with the pore pressure increasing. While it in the saturated gravel soil only rises at first and then drops a simple process, the magnification of pile head in the saturated sand is lower than in the saturated gravel sand in the initial stage of vibration. But the amplification effect of pile head acceleration is more obvious than in the saturated sand in the late stage of vibration input. Cap displacement response exhibites very similar law, while the reaction with seismic wave input is slightly different from it with sine wave input.