Lessons from impact of rising of ground water level on underground engineering in Tokyo

The geological conditions of groundwater can be changed by the artificial retaining structures and waterproof curtains for underground engineering. In addition, change of groundwater level will impact the construction or operation of underground engineering. Much attention is paid to the dewatering and land subsidence problems, but little paid to the impact of rising of groundwater level. Tokyo has the most complicated underground engineering system in the world. The groundwater level had decreased before 1970 and has risen after 1970. The mean rising is 15 m, while the largest rising, about 60 m, is recorded in the central ward. The impacts on the existing substructures, such as leakage, floating and corrosion problems, are analyzed. It is concluded that it is more important to predict and control the groundwater under operation than that during the construction period because the hazards induced by the rising of water level are more urgent, and it is much more difficulty to take countermeasures. The lessons are significant for the development and utilization of underground space, especially in the coastal cities, inland basins and northern regions in China.