2021 Volume 21 Issue 1 Pages 1_46-1_63
The Kumamoto Earthquake (Mj = 7.3) on 16th April, 2016 caused damage to civil engineering structures and buildings in the epicentral region due to two strong seismic motions and liquefaction. Road embankments near Mashiki Town suffered subsidence of the backfill after the earthquake in a wide area and the subsequent level difference behind abutments caused severe disruption to post-earthquake traffic. In this study, field investigation and numerical analysis were conducted to examine the reality and causes of the damage, targeting Kiyama River flowing through Mashiki Town in view of the conspicuous level difference damage behind abutments. As a result, it was found that subsidence of the road embankment observed at the survey sites was mainly caused by liquefaction of the sandy ground under the road embankment and consolidation subsidence of the embankment due to dispersion of the excess pore water pressure. Moreover, the survey results in the longitudinal direction of the road embankment indicated that although the level difference generated behind abutments was caused by subsidence of the backfill near the abutments, the impact on road function was small over the entire banking section unless there was a factor causing a significant change of the amount of subsidence. Using a series of analysis results, issues for the aseismic design of a road embankment in anticipation of a Level 2 earthquake were identified and a proposal was made for an evaluation method to estimate the amount of subsidence in the longitudinal direction of a road embankment to be laid above liquefiable ground. The applicability of this method was then verified in comparison with actual examples of earthquake damage.
