Abstract
Field observations of groundwater which may induce slope failures and landslides were conducted at mountain slopes from the1960s, and various physical models were developed at around the same time. After the 1980s, measurement techniques were developed that can acquire the data of pore water pressure fluctuations during not a snow cover period but an earthquake. With the evolution of investigation technologies, the flow processes of groundwater in slopes can now be visualized. In addition, large-scale analyses using a distributed model are possible to simulate the change in spatial distribution and flow of groundwater before and after the construction of landslide control works like drainage boring, well and tunnel. In future, observed data should be classified into types and made available as open data sets. It is necessary to improve investigation technologies to clarify the hydro-geological structure and three-dimensional groundwater flow analysis in fissured and weathered slopes. A fluidized moving body, whether generated by a slope failure, deep-seated landslide or reactivated landslide, flows down over long distances and spreads widely, causing severe damage in the lower catchment. Therefore, studies on the interaction between displacement and deformation of landslides and pore-water pressure should be conducted by indoor or outdoor experiments and numerical simulations. In addition, groundwater hydrology and hydraulics in landslide areas should be established as a new research field based on the knowledge gained from previous studies.
