Seismic analysis of segmental shallow tunnels adjacent to building foundations under soil liquefaction and its mitigation

In many densely populated cities, buried networks of urban services, such as facilities and sewage tunnels or sewer pipes are constructed adjacent to or beneath nearby building foundations. It is vital to consider the seismic interaction of shallow tunnels with these foundations in liquefiable deposits. In such circumstances, segmental tunnels are of interest due to being considered non-rigid structures, and their utilization has increased in shallow urban tunneling. Using a two-dimensional finite difference code, a shallow tunnel subjected to uplift pressures due to soil liquefaction is studied. An advanced constitutive model (PM4Sand) is employed in the numerical model along with a fully coupled Fluid-Solid solution to simulate soil liquefaction. First, a centrifuge laboratory model was used to validate the coupled hydrodynamic numerical simulations. Additionally, it allows for the use of real sand properties. The validation results indicated a good agreement between the numerical simulations and the centrifuge tests for tunnel uplift (maximum difference of 7 %) and the excess pore water pressure ratio (ru). Next, based on the results, segmentation of the tunnel lining was found to be effective in reducing ground surface uplift by 23 %. Then, a segmental tunnel lining with and without a five-story building on a combined footing foundation is considered under soil liquefaction. The interaction between the shallow foundation of the five-story building and the segmental lining highlights the significant influence of tunnel uplift on shear force, bending moment, tilting and rotation of the foundation and surface structure. Additionally, the presence of the foundation and surface structure leads to a reduction in tunnel uplift (by 29 %) and ground surface uplift (by 21 %). Lastly, a permeation grouting method has been utilized to mitigate seismic soil-surface structure-underground structure interaction (SSSSUSI) during liquefaction, resulting in a 90.7 % reduction.