Study on Asphalt-Cement Isolation Layer for Shield Tunnels Using Seismic Fragility Curves

For shield tunnels, seismic isolation layer is an effective countermeasure to reduce structural damage during earthquakes. In this paper, the physico-mechanical properties of asphalt-cement (A-C) materials applied to backfill grouting of shield tunnels were investigated by laboratory tests. Then, fragility curves were developed by analytical approach for shield tunnels before and after setting three typical A-C isolation layers (i.e. A-C Iso-layer1, 2, and 3), which were used to express the seismic vulnerability of tunnel lining and evaluate the seismic-reduction effectiveness under earthquakes. The results reveal that A-C isolation layers are effective in seismic-reduction under excitation of low input intensity (less than 0.5 g), while its effect is not significant at high-input intensity. The fragility curves for tunnel lining after setting A-C isolation layers show less vulnerability than not setting one at all seismic intensity levels. From the perspective of damage probability, the seismic-reduction effectiveness decreases with the increasing shear modulus of A-C isolation layer. The probability of minor damage of examined tunnel lining setting up with A-C Iso-layer1 decreased from 23% to 15% at most.