Permanent increments of internal forces on a tunnel lining due to dynamic loadings

摘要

The seismic design issues for shallow tunnel design are often poor or absent in the currentrnnational or international recommendations. Moreover, the available simplified formulations for the evaluationrnof tunnel internal forces, induced by seismic actions, account only for transient effects due to wave passage.rnSome centrifuge tests on circular tunnels in dry sand, recently performed, showed that permanent increments ofrninternal forces clearly arise in the tunnel lining after seismic events. This evidence is also confirmed in real scalernmonitoring of tunnels,which suffered residual stresses after strong earthquakes. In order to capture the permanentrnincrements of internal forces on a tunnel lining due to dynamic loadings, a series of numerical analyses havernbeen performed by using a material model which includes hardening plasticity and the strain dependency ofrnstiffness and damping.A experimental set of centrifuge tests in sand was used to validate the numerical analyses.rnThe influence of the soil-lining relative stiffness and of the shear stress transmission at the interface between thernsoil and the lining are discussed in the paper.