Fault zone determination and bedrock classification through multivariate analysis; Case study using a dataset from a deep borehole in the Mizunami Underground Research Laboratory

Abumi, Kensho*; Amano, Kenji  ; Koike, Katsuaki*; Tsuruta, Tadahiko  ; Matsuoka, Toshiyuki

Fault zones are treated as essential elements for evaluating the underground geological environment and the engineering performance of rocks. Because of the limitations to borehole investigations, it is not always possible to obtain sufficient, high-quality geological data. In addition, the evaluation of results may differ depending on various factors such as geological conditions and skill of the engineer. Such uncertainty can lead to difficulty in evaluation and understanding of the geological environment at depths and in the decision-making and planning of underground construction, which, as a result, may increases potential risks during construction. To reduce the uncertainty, this study proposes a correct selection method of data item for multivariable analyses composed of principal component analysis and clustering method using a deep borehole data. Utilizing this method and the analyses, the rocks could be accurately classified depending upon their geological characteristics.