Fracture analysis in crystalline rock with method of multivariate analysis

Ogata, Nobuhisa ; Osawa, Hideaki  ; Semba, Tsuyoshi ; Yanagizawa, Koichi

In order to groundwater flow in rock formation, it is essential to make a topographic and hydrogeological models and to set up the initial and boundary conditions. Hydraulic properties are considered to be dominated by various factors of fracture (i.e. width, density, network) in the crystalline rock. Investigated was relationship between the hydraulic conductivity. which is one of important factors for evaluation of groundwater flow, and the fracture properties, using the method of multivariate analysis such as multiple regression analysis and cluster analysis. A total of 56 data on hydraulic conductivity and physical parameter were used that had been obtained from 2 boreholes drilled in the granitic rock of Tono area, Gifu, in the central Japan. The results are as follows: (1)The results of these two multivariate analysis are almost consistent. The hydraulic conductivity in the granitic rock is dominated by fracture system, such as number and width of the fracture, fissure-filling minerals. (2)The classificatory structure which obtained from the cluster analysis corresponds to that from hydraulic conductivity. Different hydraulic conductivities were distributed in each cluster that is dominated by width of open fracture, filling minerals, number of intersect and predominant direction of fractures. (3)The cluster analysis also implies that fracture properties of test sections with the similar hydraulic conductivities occasionally differ among them. Hence, the classifications is must be made based on the data of fracture properties as well as hydraulic conductivities. Future studies using sufficient number of data is necessary.