EXPERIMENTAL STUDY ON THE INFLUENCE OF GROUND PRE-IMPROVEMENT ON SEISMIC BEHAVIOR OF SHALLOW OVERBURDEN TUNNEL

In the pre-ground improvement method, the ground around the tunnel is applied by the replacement method or the improvement method. In previous researches, the optimum ground improvement area was discussed through the numerical simulations at the excavation process. However, the seismic behavior of the tunnel was not clearly discussed. In this study, dynamic centrifugal model experiments under a gravi-tational acceleration of 50 G were conducted to clarify the dynamic behavior of the shallow tunnel with pre-ground improvement. In addition to the simple tunnel without ground improvement, two ground improvement patterns; (1) the ground around all the cross-sections of the tunnel was improved, and (2) the ground around the crown of the tunnel and the top section was improved, were investigated. From the re-sults, it is confirmed that when the entire ground around the tunnel was improved, shear deformation of the tunnel could be suppressed by the increment of the whole rigidity of surrounding ground. On the other hand, when the ground around the tunnel crown and the top section was improved, the response of the tunnel was amplified by the concentration of the weight at the upper part of the tunnel. Moreover, large cross-sectional forces were generated at the boundary between the improved and unimproved ground.