1-G SHAKING TABLE TESTING FOR SOIL RESPONSE UNDER VERTICAL ACCELERATIONS

Recently there has been substantial field evidence worldwide demonstrating that in near-fault areas numerous local and global collapses of structural systems were caused by the devastating effects of the coupling between vertical and horizontal components of earthquake ground motions. Geotechnical studies on near-fault effects and the behaviour of soils under vertical seismic excitation are still lacking. The experimental testing project on large-scale models presented in this paper aimed at improving our understanding of the vertical earthquake component for near-source conditions and its propagation on the uppermost soil layers. Specifically, the experimental campaign applied carefully selected vertical seismic excitations to a tall cylindrical soil column contained in a vessel that minimises boundary friction effects. Tentative analyses of the data confirm available analytical results: the measurement of the P-wave velocity allowed the validation of the theoretical formula for the vertical period; the amplification amount of the vertical input motion, measured by means of accelerometric data recorded at the base, along the soil columns, and at the soil surface, confirmed that the vertical amplification is significant. The success of this experimental project stimulates further investigations on more complex soil-foundation configurations.##################################################