LAUSR

Abstract Earthquake-induced liquefaction of soils can result in floatation failure of lightweight buried structures such as tunnels, with the potential for economic and human loss. Ground improvement around a tunnel is one approach to preventing this mode of failure. Four 1-g shaking table tests have been conducted including a reference test with a tunnel in unimproved liquefiable ground, and three tests with different geometries of coarse-grained granular backfill replacing areas of the liquefiable layer around the tunnel. It was observed that ground improvement performed below the tunnel was most effective at reducing uplift during earthquake loading. This was attributed to the reduction of excess pore water pressure (EPP) acting on the tunnel invert and the restriction of the flow of liquefied soil around the tunnel needed to facilitate the uplift. In contrast, ground improvement above the tunnel showed very little benefit in reducing uplift compared to the reference test. The ground improvement above the tunnel was unable to retain sufficient shear strength to restrain the buoyancy of the tunnel and, once uplift had been initiated, was unable to restrict the flow of liquefied soil that would have restricted the uplift to a small value. This suggests that, for shallow tunnels, restricting the flow of the liquefied soil and alleviating EPP acting on the invert is more important than preserving shear strength above the tunnel when designing remediation schemes against uplift.