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On the transversal seismic response and
analysis of shallow rectangular and circular
tunnels
Kyriazis Pitilakis & Grigorios Tsinidis
Aristotle University, Thessaloniki, Greece
ABSTRACT
Tunnels constitute critical components of the utility and transportation networks of urban areas. In this context, their
seismic design in seismic prone areas is of great importance. Several features of this type of constructions render their
seismic behavior distinct compared to that of above ground structures, while critical issues related to this behavior are
still open, calling for further investigation. The paper summarizes the main findings of an extensive study on the
transversal seismic behavior and analysis of circular and rectangular tunnels, which was recently carried out at the
Aristotle University, Thessaloniki, Greece. The effects of soil-tunnel relative stiffness, soil-tunnel interface conditions and
soil yielding on (i) the deformed shapes of tunnels during shaking, (ii) the dynamic lining forces, and (iii) the dynamic
earth pressures and dynamic soil shear stresses developed around rectangular tunnels, are discussed on the basis of
results from recent dynamic centrifuge tests and rigorous numerical analyses. In parallel, the efficiency of a wide range
of simplified analysis methods, which are often implemented in the tunnelling design practice, is also highlighted and
discussed. Particular emphasis is given on the experimentally and numerically proved coupled racking-rocking response
of shallow rectangular tunnels subjected to transversal ground shaking. A series of numerical racking ratio - flexibility
ratio (R-F) relations are developed for a wide range of soil-tunnel configurations, quantifying the racking response of
rectangular tunnels, while the rocking response is quantified by means of dimensionless tunnel section rotation flexibility ratio (θ/γff-F) relations. An improved set of design racking ratio - flexibility ratio (Rd-F) relations that account for
the combined racking-rocking response of tunnels is finally provided, contributing towards the improvement of the R-F
method. The presented results lead to a better understanding of the transversal seismic response of shallow tunnels in
alluvial soil, highlighting the advantages and shortcomings of various analysis methods, hence contributing to increased
safety margins of the seismic design of tunnels.