Seismic interaction of tunnel-building systems on soft clay

Abstract

Seismic performance of structures located in urban areas, such as midrise buildings, can be significantly affected by its interaction with underground facilities, such as tunnels. To date however, there is still a lack of proper understanding regarding the interplay between incoming seismic waves reflected in underground infrastructure, and the energy feeding back from surface structures swinging back and forth during a large earthquake. In particular, due to its complexity, the effect that underground tunnels have in the seismic response of medium to low rise buildings is often ignored or its assessment is over simplified in practice. This, in turn, can lead to unsafe or costly designs. This paper presents a numerical study aimed at closing the gap in numerical data regarding the potential area of influence in which ground motion variability is strongly affected by the presence of an underground tunnel, and more importantly, the actual impact in the structural building seismic performance. This study is focusing on tunnel-building systems located in soft clay deposits, slightly intercalated by layers of silty sands and sandy silts, such as those found in Mexico City. Series of three-dimensional finite difference models were developed to study the proximity effect of the tunnel to the building, in the computed building structural response. From the results gathered in here, it was evident the ground motion modification in the surrounding soil that occur mostly in the transversal ground motion component due to tunnel-building interaction, establishing detrimental or beneficial soil-structure interaction effects, for both normal and subduction events.