Simplified modelling of the transient response of underground structures due to dynamic loads generated from underground tunnels

Underground tunnels are widely used nowadays in major cities resulting in a significantly congested underground space. In many cases they are located close to underground structures, such as foundation piles, retaining walls etc. and civil engineers need to assess the interaction between tunnels and such structures. Although static tunnel-structure interaction has been widely studied over the past decades, there are still aspects of dynamic tunnel-structure interaction that still need to be clarified. Such dynamic interaction may arise in cases of vibration from high-speed railways close to buildings or in cases of explosions in tunnels. Both of these two cases involve transient dynamic loads but they differ in their frequency content, duration and amplitude. This study aims to assess the transient dynamic response of underground structure due to dynamic loads generated in underground tunnels. A simplified two-dimensional plane-strain finite element model, with a simple tunnel and buried wall geometry, is developed using a dynamic time-domain formulation. Two different input dynamic loading regimes are considered and the dynamic response (accelerations and displacements) of the top of the structure is evaluated. Different aspects of the model are discussed, including the effect of the modelled dynamic boundary conditions and the most critical time of the structural response.