コアディスキングにおけるディスク厚さと地圧の大きさの関係

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Core discing occurs due to tensile stress induced by boring within or below a core stub. To determine effects of the length of core on the magnitude and direction of tensile principal stress, a finite element analysis was carried out for an HQ core with different lengths for 77 in-situ stress conditions. We analyzed the semi-axial tensile principal stress, which is inclined from core axis by less than 45°, and the maximum semi-axial tensile stresses were determined with respect to the core axis for each position of the cross-section of the core. The minimum value and the mean inclination relative to the core axis of the maximum semi-axial tensile stresses were analyzed to determine the stress condition under which core discing is likely to occur. As a result, 30 in-situ stress conditions were identified as the stress condition under which core discing is likely to occur and the necessary condition for the in-situ stresses was proposed. The critical tensile stress, which is the maximum tensile stress that can produce a tensile fracture propagated throughout a cross-section, was analyzed for these stress conditions and a new criterion for core discing, which can be applied to any length of core, was proposed. Stress conditions estimated by the criterion were consistent with previous experimental results for a long core and for discs with small thickness. According to the criterion, the relationship between the length of core and the in-situ stress necessary for core discing was discussed, which showed that the stress field can be divided into three regions and that core discing with small length mostly occurs at great depth. The relationship between the length of core and the thickness of disc was determined by assuming that the position of a fracture is given by the mean position of the maximum semi-axial tensile stresses. Theoretical estimation reproduced previous experimental results on the effects of stress magnitudes on the thickness of disc.
2002-11-25

コアディスキングにおけるディスク厚さと地圧の大きさの関係

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