11. Analysis of Liquefaction During 2011 East Japan Earthquake – Part 2: Effective Stress Analysis Considering the Permeability of the Ground ~ Liquefaction at Reclaimed Land in the Main and After Shocks of the 2011 Great East Japan Earthquake

A series of effective stress dynamic analyses considering permeability was performed in areas with and without liquefaction damage at reclaimed land in Urayasu city in the Tokyo Bay area due to the 2011 Tohoku Earthquake off the Pacific coast. Liquefaction damage was significant because the ground shook with earthquake motions for an extremely long duration (more than 2 min for the main shock) followed by an aftershock about 30 min later. In particular, the delayed sand boil, which occurred much later than the main shock, was monitored by a security camera at the site. In typical earthquake motions with a shorter duration, the permeability of the ground is ignored in the seismic response analyses. However, whether the effect of permeability can be ignored becomes questionable when the duration of earthquake motion is extremely long and additional effects occur due to an aftershock such as the case with the 2011 earthquake. The results of the effective stress analyses incorporating the effect of permeability are consistent with the behavior of the ground with and without liquefaction damage. In particular, the delayed sand boiling at the liquefied site is well simulated by the effective stress analysis for a specific combination of permeability assigned above and below the groundwater table, indicating that it is important to carefully evaluate the permeability in the analysis of liquefaction.