Soil-structure interaction of shallow tunnels in liquefiable soils during strong earthquakes

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Underground structures in general and tunnels in particular are essential components of sustainable and efficient transportation system in fast growing cities. They will play even a more important role for the implementation of automated driving systems in the near future. The economic and social costs associated with structural loss or even a long-term interruption of service are huge and only acceptable with a very small probability of occurrence. In addition to static loads, mainly resulting from the soil and groundwater, tunnels in seismic regions must withstand earthquakes. The behaviour of tunnel structures under these conditions is dominated by the interaction between the surrounding soil and the tunnel structure (SSI). While the mechanism of the SSI under static and weak to moderate seismic loads is well understood and can be properly addressed during design, the behaviour of tunnel during strong earthquakes is still in the focus of research. Particularly, shallow tunnels in liquefiable soil are one of the most challenging problems in tunnel engineering.The joint research of Tongji-University (TJU) and Technical University of Munich (TUM) will provide a robust numerical approach and a unique experimental database to analyse and predict the seismic response of shallow tunnels in liquefiable soils during strong earthquakes. The numerical approach not only will enable the assessment of the impact of liquefaction on tunnel structure and provide the basis for risk-informed decision-making, but also will allow for computer-aided design and optimization of the required mitigation measures under consideration of the relevant geotechnical and structural risks associated to SSI problem.The joint research consists of two phases. In the first phase, the individual components of the SSI problem (soil, tunnel and soil-tunnel interface) will be investigated and the corresponding constitutive models will be validated. The experimental program is highlighted by newly set up element tests, a unique multidirectional shaking table tests, and tests using a geotechnical centrifuge. The second phase will be devoted to the development of a comprehensive SSI model based on the results of first phase.The collaborative research largely benefits from mutual complementary experience and knowledge transfer as well as the advanced experimental facilities available in particular at the Structural Experimental Center of TJU. Specifically, the possibility to combine large multi-directional laminar shakebox with centrifuge tests at TJU is unique worldwide and not currently available in Germany.