Seismic Behavior of Tunnel Structure Under Varying Surrounding Soil, Water Table, and Overburden Condition

The increasing need to expand the urban transportation systems, tunnels, and underground structures are playing crucial role in building modernized transportation networks. It has been observed during recent earthquakes that underground structures may undergo severe distress produced by excessive deformation. Hence, it is necessary to have a precise assessment of deformation, force, and moment in structures caused by surrounding soil under seismic conditions. The variation of deformation, force, and moment with varying characteristics of surrounding soil, water table, and overburden pressure due to varying depth of structure need to be assessed properly for different seismic zones. Therefore, with this in view, a parametric study has been conducted for a typical box structure of size 10.0 m wide × 6.0 m high, having different depths of 8 m, 10 m, and 12 m, encountering varying soil layers of loose to medium, medium to dense, and very dense non-cohesive soil at different seismic zones. The results of the study reveal that distortion and bending moment reduces by 14–22% and 15–22%, respectively, when compactness of subsoil surrounding the structure changes from loose to medium and further to dense under the same seismic conditions. Deformation also reduces by 4–7% due to increase in tunnel depth from 8 to 10 m and then to 12 m. On the other hand, deformation becomes almost double when seismic zone changes from III to IV for the same soil condition. The outcome of the present study may be useful to the practicing engineers in design of underground structures.