Seismic response of irregular underground structures under adverse soil conditions using shaking table tests

A series of large-scale shaking table tests were performed to investigate the seismic response of an underground subway structure with irregular sections in adverse soil conditions (soft and liquefiable sites). Emphasis is placed on the influence of the adverse soil conditions on the response of the irregular underground structures and over areas of soil-structure interface, involving buildup of pore pressures and resulting large deformations. The results indicate that the seismic responses of the structure and the soil were sensitive to input motions with richer low-frequency components. The seismic damage of the underground structure was more significant in the soft site as compared with that in the liquefiable site. The liquefiable site worked as a natural seismic isolation system for the underground structure, significantly reducing the damage potential to the model structure. Under the action of a strong earthquake, the horizontal displacement response of the liquefiable site sharply increased compared with that of the soft site. With respect to the structure response, the interlayer displacement of the structure in the soft site was approximately twice that in the liquefiable site. The lateral deformation of the structure was greater in the soft site and the interior structure column was more prone to damage. Correspondently, the peak and the residual strains in the structural components in the soft site were higher than those in the liquefiable site were. The results provided insights into the site effects of adverse soil conditions on the seismic response of underground structures, especially on the seismic damage process and the failure mechanisms of the structure members.