Influence of Surrounding Soil Condition on Earthquake Damage Response of Underground Frame Structures

During the Kobe earthquake in Japan, different degrees of earthquake damage occurred on the Daikai subway station and Kusokunagata subway station. These two stations have almost the same structure construction but different surrounding soil conditions. Based on nonlinear finite element analyses, influences of surrounding soil condition on earthquake damage response of underground frame structures were investigated. Numerical results indicate that different surrounding soil conditions lead to different seismic responses of the Daikai station with those of the Kusokunagata station. The horizontal relative deformation between the soil layers which are located at the same depth with the structural lower end and upper end of the Daikai station is significantly greater than that of the Kusokunagata station. Therefore, the horizontal relative deformation of structural lower end and upper end comparison of the two stations is also the same. The excessive lateral deformation and the high axial compression ratio jointly made the brittle failure appear in the columns of the Daikai station, which leads to the overall disrepair of the structural frame. Whereas, little lateral deformation appeared in the column of the Kusokunagata station because its response to the earthquake did not exceed its loading limit and the entire station survived during the earthquake.