Verification of Improvement Effectiveness by Compaction Methods During the 2011 off the Pacific Coast of Tohoku Earthquake

The 2011 off the Pacific Coast of Tohoku Earthquake caused severe liquefaction of reclaimed lands in the Tokyo Bay area. Prior to the earthquake, many ground improvement works have been implemented in reclaimed lands along Tokyo Bay and no damage was observed at any of the improved sites. The main purpose of ground improvement in this area was liquefaction prevention and most of the countermeasures implemented were compaction (densification) methods, such as vibratory and non-vibratory sand compaction pile (SCP) method. This paper presents the conditions of the area after the 2011 earthquake by comparing the performance of unimproved and SCP-improved areas in terms of the distribution of the normalized N-values, fines contents, and the corrected N-values based on pre- (unimproved ground) and post-(SCP-improved ground) boring logs along Tokyo Bay. In addition, the relationship between the corrected SPT N-values in the improved grounds and the shear stress ratio estimated using the maximum surface acceleration obtained from recorded motions near the site was analyzed.