Shaking table test on the acceleration amplification effect of platform-canyon combination topography

In mountainous regions, the complex interplay between topography and geology significantly influences seismic wave propagation and amplification, posing considerable challenges to engineering seismic design. This study investigated the seismic amplification effects of platform-canyon combined topography through the shaking table tests. A scaled model with symmetrical geometry but distinct geological configurations (loess on the left side versus granite-overlain-by-loess on the right) was subjected to various seismic and sinusoidal excitations with peak accelerations ranging from 0.1g to 1.2g. The horizontal and vertical dynamic responses, characterized by the ground motion amplification factor (GMAF), were systematically analyzed. The main findings were as follows. First, the topography exerted a dominant control on the horizontal response. The less-constrained platform triggered a pronounced "whip effect," resulting in a peak horizontal displacement 20%-50% greater than that of the canyon, with the maximum horizontal GMAF (up to 3.03) occurring at the platform crest. Second, the geological structure significantly modified the surface response. The model side with an underlying granite layer exhibited a 36.3% stronger amplification (coefficient up to 4.13) compared to the side with a single loess layer, highlighting the role of higher elastic modulus. Third, resonant amplification was governed by the coupling between the site's natural frequency and the input wave spectrum. A local GMAF of 6.74 was recorded under specific frequency-matching conditions (10 Hz - Kobe wave). Finally, the vertical response exhibited high-frequency selectivity and spatial heterogeneity, being more pronounced on the granite side and at frequencies exceeding the site's vertical predominant frequency (20 Hz). These results quantitatively elucidate the amplification mechanisms arising from the combined influence of complex topography and variable geology. The findings provide a crucial experimental basis and theoretical reference for the seismic design and risk assessment of engineering structures in mountainous areas.