Study on Asphalt-Cement Materials for Seismic Isolation Layer of Shield Tunnels

Abstract

Shield tunnels have been extensively used in many fields and are exposed to the threat of earthquakes. Seismic isolation is an effective anti-seismic method to protect tunnels from earthquake damage. This study investigates asphalt-cement (A-C) materials used as a seismic isolation layer of a shield tunnel by backfill grouting. Both a uniform test and comparative test were conducted to study the grouting properties of A-C materials. The experimental results indicated that an increase in cement content significantly affects the fluidity and consistency of A-C materials. The ultimate compressive strength increased with increasing cement content, and the recommended mass ratio of cement/asphalt for the seismic isolation layer was 50%. Then, a planned shield tunnel crossing hard-soft stratum junction was taken as the research object, and the seismic response of the tunnel lining with different fortified lengths of A-C seismic isolation layer was analyzed by numerical simulation. The calculation results show that the tunnel lining located at the hard-soft stratum junction is vulnerable to damage under seismic action, and the A-C seismic isolation layer can significantly reduce the maximum principal stress of lining near the junction. The reasonable fortified length of the A-C isolation layer for the examined shield tunnel is 3.5 times the tunnel diameter from the stratum junction to both sides.