Physical modelling of the interaction between a tunnel and a building in a liquefying ground and its mitigation

Abstract

The fast growth of the built environment in liquefaction-prone areas requires new design challenges to be overcome. A significant soil shear strength and stiffness loss associated to soil liquefaction, possibly occurring during severe earthquakes, may induce effects on buildings and on shallow and light structures such as urban tunnels. In densely urbanised areas, interaction between underground and aboveground structures may results in a detrimental combination of such effects.The paper discusses the results of a series of centrifuge tests carried out at the Schofield Centre (Cambridge, UK) modelling the dynamic interaction between an urban tunnel and a building in sand undergoing cyclic liquefaction. Four reduced-scale models were tested at increased gravity to model a prototype 60 times larger. A rectangular aluminium frame embedded in a layer of homogeneous Hostun sand represented a section of a metro tunnel. An aluminium sway frame represented a simple building founded in the same layer, at a side of the tunnel. The experimental results show that in typical urban spacing, sand liquefaction in the foundation ground affects the reciprocal interaction between the kinematic of the tunnel and the building.Centrifuge modelling investigated whether it is possible to mitigate or prevent such interference by improving ground through the addition of hydrated laponite beneath the tunnel floor or as lateral vertical barrier between the building foundation and the tunnel. The results also show the importance of temporary structures – often used to support soil excavation during cut-and-cover tunnel construction – in reducing the effects of interaction between the tunnel and the building in the liquefying soil.