Challenges of landslide prevention work completion methods and the management after a project under direct control

Landslide prevention projects are used at five stages: (1) designation of landslide prevention areas, (2) formulation of master plans, (3) construction of landslide prevention works, (4) completion of projects, and (5) post-project management. However, (4) and (5) have no universal standards. Local rules are used for individual areas. For these stages of (4) and (5), this paper presents four points as difficulties for the Kochi Sanbagawa belt area. Its current state and expected outcomes were assessed. First, landslide blocks were identified. Correct evaluation and identification are necessary for a landslide block to be processed as a unit during management. Topographical analysis is the main method used today. However, results from GPS, aerial laser measurements, SAR interferometry, and other methods are also considered. Furthermore, more accurate and simplified investigation methods are anticipated. Second, evaluation and prediction of groundwater conditions must be done after building construction. Systematization of a certain degree is necessary for application of an analytical method, including the identification of subterranean stream networks using water quality analyses. Current methods rely on trial and error at individual sites. Third, judgment of a standard of the completion (Gaisei) is necessary. Such standards are often produced separately at different sites based on an empirical rule, but many contents must be handled as present criteria of control. The techniques to manage slope risk by assessing rainfall and groundwater effects on the amount of displacement of a landslide must also be considered. Fourth, slope management must be done after project completion. Different ideas must be examined in order of priority, with slope management emphasizing landslide measurement facilities and simple observation methods. Realistically, it is costly to maintain observations of ground displacement throughout a landslide prevention area during implementation of countermeasure work. Future methods are expected to provide continuous observations and function indicators at each measurement facility. Moreover, a risk evaluation method must be developed for a whole slope with multiple measurement devices and observation methods.