Numerical analysis and seismic design of shallow tunnels in soft alluvial deposits

Abstract eng:
The scope of this paper is to investigate the efficiency of several approaches concerning the seismic design of long underground structures. For this purpose, the case of Thessaloniki immersed roadway tunnel is employed, as a means to validate and discuss different analysis approaches in a real problem. Closed-form solutions, imposed free-field deformations at the side boundaries of the soil-structure system, as well as equivalent static analysis are investigated, regarding their efficiency in reproducing the actual tunnel behavior under seismic loading in the transversal direction. One-dimensional site response analysis is utilized to calculate several parameters of the input motion, including the free-field deformation and acceleration variation with depth. A full dynamic time-history analysis scheme is employed to evaluate the aforementioned simplified methods, being able to capture the transversal dynamic soil-structure interaction phenomena that develop during the seismic shaking more accurately. Comparative study of simplified and more sophisticated numerical analysis indicates that in some cases there are important differences between the examined methods. Although certainly simplified, the presented analysis approaches provide, under certain conditions, a cost-effective approximation to study the response of underground structures under earthquake loading. Yet, the application of these methods needs to be further improved, in order to facilitate their use in practice and allow for their implementation in engineering applications.

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