Abstract: 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.

Key words: deep riverbed overburden, soft soil layer, dynamic characteristics