含软弱土层的深厚河床覆盖层坝基动力特性研究

在强震区、含软弱土层的500 m级特厚覆盖层上建坝,超出了现行设计规范的控制范围。开展了覆盖层厚度、输入地震波峰值、覆盖层中的软弱土层厚度等指标的敏感性分析,揭示了深厚覆盖层地震反应的主要特征及坝基建基面加速度放大倍数分布的规律性。研究认为:覆盖层厚度、输入加速度峰值、软弱土层厚度等指标与建基面放大倍数的衰减在变化规律上成正相关;当输入地震波峰值加速度为0.5g作用下,含软弱土层的500m级特厚覆盖层坝基中地震波总体以衰减为主,建基面放大倍数小于1;覆盖层加速度放大倍数随高程变化的基本规律为先衰减后放大。当存在软弱土层时,由于其滤波隔震作用会在土层内发生动力反应的二次衰减。基于上述分析,进一步提出了覆盖层下部区域地震效应衰减、中部区域软弱土层二次衰减、顶部区域放大的加速度放大倍数分布模型,编制了覆盖层加速度放大倍数建议值表,研究成果可为含软弱土层的深厚河床覆盖层坝基工程设计提供重要参考。

Study of dynamic characteristics of dam foundation on deep riverbed overburden with soft soil layer

The construction of dam on the 500 m-level thick overburden with soft soil layer in a strong earthquake zone is beyond the control scope of the current design specification. Through the sensitivity analysis on indicators such as overburden thickness, peak of input seismic wave and thickness of soft soil layer, the main characteristic of the seismic response of deep overburden and the distribution regularity of foundation surface acceleration amplification factor of the dam foundation are studied. According to the research, the overburden thickness, input acceleration peak and soft soil thickness are positively correlated with the attenuation of the amplification factor of the foundation surface. When the peak acceleration of the input seismic wave is 0.5g, the earthquake responses in the 500-level ultra-thick overburden layer with weak soil layer are mainly attenuated, and the magnification factor of the foundation surface is less than 1. The basic law of the acceleration magnification of the overburden layer is first attenuation and then amplification with the elevation change. When there is a weak soil layer, the secondary attenuation of dynamic response will occur in the soil layer due to its filtering and seismic isolation effects. Based on the above analysis, an acceleration amplification factor distribution model of the attenuation of the overburden layer’s lower part, the secondary decay of weak soil in the central area, and amplification of the top area are further proposed. A table of recommended values of overburden acceleration magnification factor is compiled. The research results can be used as a reference for future engineering design of dam foundation on deep bed overburden with soft soil layer.