Numerical simulation of borehole shape focusing on strain localization

For the construction of a URL for HLW geological disposal study, characterizations of rock structures have been carried out in Horonobe, Japan. In borehole investigation, breakout phenomena were observed at depths. Rock failed where the resultant stress exceeded the shear strength of the rock. This paper reports the result of a numerical simulation of the borehole breakouts, using a strain-softening type elasto-plastic model. In the analysis, the initial stresses are estimated, referring to the results of in situ stress measurements by hydrofracturing technique. As a result it is found that the result of the numerical simulation is in general consistent with that observed in the field. (author)