Keynote Lecture – Missing issues in mitigation of rainfall-induced landslides
In both understanding the causative mechanisms and designing mitigation measures, landslide has been one of the most important applications of soil mechanics. Therein, those issues such as drained/undrained shear strength, rate of loading, pore water pressure and geological structures have been studied profoundly. Although being similar to traditional landslides, the rainfall-induced landslide has special features. First, it occurs suddenly during heavy rain at places where there has been no sign of imminent failure. There is hence no time to carry out monitoring and to reinforce suspected slopes. Obviously there is no time for a vulnerable community to be relocated to safer places. Second, it seems that the underground hydrology during heavy rain exerts significant effects on the pore water pressure, effective stress and shear strength of surface soil that are going to fall down. The flow of underground water is extremely difficult to study over a big region with limited budget. Third, the potentially unstable soil mass is small in size but many in numbers. It is hence nearly impossible in a practical sense to investigate the subsoil conditions in all of them. Even more difficult is the lack of information on the progress of weathering and deterioration Despite those difficulties, people urgently desire safety from natural disaster and engineers are required to propose good safety measures. The author has been facing these problems in the recent times and provides some empirical lessons and measures that can improve the situation. Even a simple underground survey is able to demonstrate a key issue that controls the future risk of slope failure. Although early warning is very good measure to reduce human loss during slope failure, it still has difficulties in its application to the practice.