Case study of applicability of active drainage work from slope

Hiroaki NAKAYA, Akira GOTO, Toshihiro IMAMURA, Keiji MUKAI and Ryosuke TSUNAKI

Mass wasting and landslides have claimed sizable human casualties in Japanese archipelago for a number of years. Herein lies the importance of mitigation works (thereafter “sabo works"). Nevertheless, the cost performance of sabo works has not seen an upward trend. Financial constraint drives us to make further effort to upgrade now age]old engineering methods substantially. This case study describes an attempt to apply a combination of drainage pump and air]vacuuming pump, a kind of active drainage method. The study leads to a comprehensive cost performance analysis in relation to gravitational drainage wells with lateral boreholes, which are in wide use. The combination allows us to get over the engineering depth limits of pumped wells, whether the pumping apparatus may be put down at the bottom end or on the ground surface. Multifaceted evaluation of field testing during two consecutive seasons shows that the combined application of pumps could have advantages, in terms of cost, to existing gravitational drainage methods about three to five times, not only for short time but also for forty]year period. Their site specificity is to be taken into consideration carefully throughout the analysis.

Key wordsFactive drainage, combined pump, cost performance