抄録
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－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.
