Case Study of Soft Ground Countermeasure with More than 100M Thickness in Japanese Expressway

Abstract

This study shows the vacuum consolidation method in the soft ground section of about 3 km length at the construction site in Japanese Expressway. This soft ground is covered with high soft organic soil under the ground level, and soft clay soil, loose sandy soil and this highly soft organic soil are deposited as the mutual layer at the bottom part within more than 100 m thickness. Soft ground has a possibility to cause a serious problem at the maintenance stage when the long-term large scale settlement happen, however, there was no experience of expressway construction on such a quite thick soft ground in Japan. Therefore, full scale test embankment was constructed to confirm the effective method. Vacuum consolidation method was adopted from the result of full scale test. By this method, the construction cost can be reduced by about 60% compared with the deep mixing treatment method, and the construction period has been shortened by about 50%. Total settlement amount for 10 years is estimated to be around 10 to 20 cm based on the analysis of observation during construction.