EXPERIMENTAL EVALUATION OF SEISMIC SITE RESPONSE OVER AND NEARBY UNDERGROUND CAVITIES (STUDY OF SUBWAY TUNNEL IN CITY OF KARAJ, IRAN)

The effect of underground cavities in site seismic response was studied over the subway tunnels that are under construction in the city of Karaj, using ambient noise measurements as well as numerical modeling. The idea for this research comes from the observation of differences in experimental site transfer function, calculated on more than 100 locations of the city, for the areas near the under construction subway tunnel, compared with other parts of the city. In the present study a series of multi stations ambient noise measurements at 11 test sites across the tunnel were performed to evaluate the effect of the tunnel on seismic site response. This paper shows the results of these measurements as well as the result of a numerical modeling for one of the locations. The results show that the site effect in areas near the tunnel are affected by tunnel and vary based on dimension of excavation and distance from tunnel axis.