Shaking table tests on liquefaction mitigation of embedded lifelines by backfilling with recycled materials

The 2011 off the Pacific Coast of Tohoku Earthquake caused significant damage to embedded lifelines in the Tokyo Metropolitan area. In particular, the floating of embedded sewage pipes and manholes was widely observed on recently constructed artificial islands, where liquefaction took place both in loose backfill soils and the surrounding subsoil. This problem should be addressed in earthquake-prone regions where future earthquake risks are a concern. Thus, the aim of the present study is to develop new backfilling methods using recycled or economical materials to mitigate the liquefaction-induced floating of sewage pipes. The examined recycled materials were crushed glass, crushed concrete, a mixture of tire chips and sand, and cement-treated liquefaction ejecta. Several series of shaking model tests were conducted to investigate the performance of the recycled backfill materials. The proposed methods are to be used when old or damaged pipes are replaced by new ones where the excavation of backfill soils is required. The influence of liquefaction in the surrounding subsoil on the performance of improved backfills constructed of recycled materials was also taken into account. The model test results showed that the examined materials are useful for mitigating the liquefaction-induced floating of buried pipes irrespective of the liquefaction potential in the surrounding subsoil. The importance of balancing the unit weight of the backfilling materials and the surrounding subsoil was highlighted for enhanced safety when the surrounding subsoil was liquefiable. In particular, crushed glass showed the most promising performance for preventing pipeline damage caused by liquefaction.