Présentations Colloques

Oral Presentation
8.03
Session 8.03: Geometrical structure and hydrogeological properties of Hard-Rock aquifers.
Kashiwaya Koki
In-situ measurements of permeability and development of a hydrogeological model that considers the permeability distribution around a fault in the Toki granite, Japan
Faults have various roles in hydrology and there is concern about their influence on groundwater flow and mass transport. We used the Mizunami Underground Research Laboratory (Japan Atomic Energy Agency) in Mizunami, Gifu, Japan, as our study site. This laboratory comprises shafts and horizontal tunnels of different depths, and one of the shafts is adjacent to a vertical fault that is referred to as the “Main-shaft fault”. These research tunnels are distributed mainly in the Toki granite, and we measured the permeability of the Toki granite at 138 points in the walls of horizontal tunnels at depths of 200, 300, and 500 m with a mini-permeameter (MP-401, TEMCO Inc.). We then applied the MODFLOW hydrogeological model, developed to consider the permeability distribution, to analyze and provide an improved understanding of the groundwater flow regime around the fault.**The results of the measurements showed that permeability decreased with distance from points at which local maximum values were observed, and with distance from the fault plane. There was more variability in the permeability in more deteriorated parts of the granite. There is a 40-m-wide zone of low permeability around the fault plane that resulted from alterations and infilling of fractures by clay minerals (Mikake et al, 2010+ Daimaru et al, 2012). These characteristics of permeability distribution were reflected in the hydrogeological model. The results of this study provide a unique insight into the groundwater flow regime in granite near a fault.**This study was supported by a grant from the Ministry of Economy, Trade, and Industry (METI). We express our sincere appreciation to all those who contributed to this study.**References**Daimaru et al., JAEA-Research 2012–008, 2012.**Mikake et al., JAEA-Technology 2010–026, 2010.**
Japan