Laboratory Verification of the Diametrical Core Deformation Analysis (DCDA) Developed for In-situ Rock Stress Measurements

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  • コア変形法 (DCDA) の室内検証実験
  • コア ヘンケイホウ(DCDA)ノ シツナイ ケンショウ ジッケン

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Abstract

DCDA is a new method for evaluating the in-situ stress of rocks based on the elliptical deformation of boring cores with stress relief. If the condition of in-situ stress is anisotropic, the core must expand elastically in an asymmetric shape. The cross sectional shape of the expanded core can be measured precisely, and the differential stress SHmax<tt>－</tt>Shmin and azimuths of SHmax and Shmin can be determined from the measured shape data. In order to confirm the reliability of DCDA, laboratory verifications were conducted focusing on a manner how the core expands with stress relief caused by drilling.We used 300 mm cube mortar specimens in which strain gages were embedded.The specimen was set into a steel frame where it was subject to an uniaxial compressive stress using a pair of flat jacks. While holding the applied stress, a core sample was drilled out from the specimen and the strain in the core was recorded. Following results are obtained; 1) The relief strain caused in the core has the same magnitude with the strain in the specimen caused by applying a uniaxial compressive stress, while those strains are opposite in sign. 2) The experimentally-observed core expansion with drilling was consistent with that predicted by a linear elastic FEM. 3) Some core bits may scrape partially the surface of the expanded core, then DCDA will underestimate the applied stress. A specially-designed core bit must be necessary for DCDA to avoid scraping the expanded core.

Journal

  • Journal of MMIJ

    Journal of MMIJ 130 (12), 515-521, 2014

    The Mining and Materials Processing Institute of Japan

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