Centrifuge Testing of the Seismic Performance of a Submerged Cut-and-Cover Tunnel in Liquefiable Soil

Centrifuge model tests were performed to verify numerical methods being used to assess the stability of a cut-and-cover subway tunnel in a highly seismic area. Since the tunnel is less dense than the backfill soils and the backfill soils are liquefiable, there is concern that the tunnel could suffer large deformations due to buoyancy forces in the event that liquefaction does occur. Numerical analyses indicated that tunnel deformations would be limited due to the dilatancy of the backfill soils, the geometry of the problem, and dissipation of excess pore pressures. The design, testing, results of the centrifuge tests are presented in this paper. The experiments provided added confidence to the design and review team that the analysis is capturing the dominant deformation mechanism. The centrifuge model tests clarified the mechanisms of deformation and are playing an important role in evaluating if a very expensive retrofit project is necessary.