Survey concerning geology and geological structure of sedimentary rock at Neogene in Horonobe-Cho, Hokkaido, Japan. Part 2

Survey was conducted for the following purpose: obtaining data on the planar variation in depth of the oxidized zone, understanding of the transition from oxidized zone through the dissolution zone to the fresh rock zone, and depicting of weathering history at near-surface in the area where the Laboratory is planned to be built and also establishing of stratigraphy and geological structure of the Neogene strata in the area around the Omagari Fault. During the survey, drilling was done at 23 sites. The standard penetration test was conducted at one drilling site (H16-1-01). Data of hardness and color degree were obtained for the cored samples at the all sites. Vinyl chloride pipes (VP50) for observation were set up after the drilling. The survey results show thicknesses of the fill(Bk), clay zone (Ac), mudstone of the oxidized zone (Ms-1), mudstone of the dissolution zone (Ms-2), and mudstone of the fresh rock zone (Ms-3) are 0.7 m, 0.1-3.3 m, 0.4-32.2 m, 1.0-12.5 m, 0.5-14.0 m, respectively. N-values in average of the Ms-1, Ms-2, and Ms-3 were 14, 19, and >50, respectively. Underground water levels confirmed by the survey were 1.1-15.46 m in depth (H=79.9-59.4 m). Average RQD of Ms-2 and Ms-3 were 8% and 45%, respectively. Hardness and color degree of the samples of Ms-3 from the fresh rock zone are: Ld-values=408, L* (brightness) = 32.4, a* (positive: red, negative: green)=0.01, and b* (positive: yellow, negative: blue)=6.7. Levels (above sea level) of the top of the fresh rock zone is higher at the higher-elevation sites compared to those at the lower-elevation sites, suggesting that the level of the top of the fresh rock zone is not very different in this area regardless of topography. There is no significant correlation between the hardness, Ld-values, of the samples and top depth of the fresh rock zone. The color degree of a fresh rock doesn't depend on the point and indicate a similar value. This work was performed by Ueyama-shisui Co., Ltd. under contract with Japan Nuclear Cycle Development Institute (JNC). (author)