2019 Volume 7 Issue 2 Pages 648-653
The hydraulic states in dike are affected by external factors such as rainfall and river water level, and have direct relevance to the safety and stability of the structure. Unsteady unsaturated seepage flow analysis based on Richards equation for water mass balance is widely used to predict hydraulic states in dikes. However, previous trials suggest that this approach tends to reproduce much higher phreatic surface than observed in field during and after heavy rainfall. One factor explaining this problem is the potential effect of entrapped air in dike. In this study, a sandy river dike along Babame River in Akita, Japan, was chosen as a study site. Along with basic site investigation and long-term pore water pressure monitoring with tensiometers, 1- and 2-phase seepage flow analysis was performed to understand the role of air impedance in light of field monitoring results. 2-phase seepage flow analysis outputs more subdued pore water pressure responses than 1-phase analysis during and after extremely heavy rainfall (more than 100mm/day). For lesser rainfalls, however, the difference between the two analytical approaches was negligible.
