Mapping of liquefaction risk on road network based on relationship between liquefaction potential and liquefaction-induced road subsidence

Abstract

On March 11, 2011, a large earthquake of Mw 9.0 shook north-eastern Japan and caused severe liquefaction-induced damage over a wide area of reclaimed lands along the coast of Tokyo Bay. Although regional mapping of the liquefaction hazard had been performed in many automounts bodies in Japan, it seems that the maps were not effectively used on all fronts of disaster-prevention management, because the maps only provide liquefaction susceptibilities and little quantitative information on how seriously the ground might deform in a scenario earthquake, which is absolutely necessary information for discussing what-if scenarios. Konagai et al. (2013) conducted air-borne LiDAR surveys to obtain liquefaction-induced ground deformations over the north-eastern stretch of the Tokyo Bay shore area, including Urayasu City, where approximately 85% of the city area was heavily liquefied. Meanwhile, the authors have developed a geotechnical database for liquefaction risk assessments, compiling all the available borehole logs and soil testing data provided by Urayasu City (2012). Given the potential risk of re-liquefaction in a future scenario earthquake, it is an overriding priority to develop a knowledge-sharing liquefaction hazard map reflecting precise records from the past, such as liquefaction-induced ground subsidence and liquefaction-related damage. This paper attempts to assess the liquefaction-induced damage risk on road network, examining the relationship between the liquefaction potential index and the actual ground subsidence. For this purpose, firstly, the spatial distribution of the liquefaction potential (PL) was estimated over Urayasu City based on the above-mentioned geotechnical database developed by the authors. Secondly, the spatial distribution of the PL values and the actual liquefaction-induced road subsidence confirmed through air-born LiDAR surveys were compared to develop an empirical rule for estimating the potential road subsidence in a scenario earthquake. This empirical rule was found to describe the actual damage to roads and manholes in a satisfactory manner. Therefore, it is expected that a risk map, developed on the basis of this empirical rule, will not only help to assess liquefaction-induced damage, but also to design countermeasures against the what-if scenarios of liquefaction.