2軸応力下の円形空洞の弾塑性変形

境界要素-特性曲線結合法による岩盤空洞の弾塑性解析 (第2報)

抄録

Elasto-plastic deformation of a circular opening under bi-axial stress condition has been analyzed on the basis of the theory of plastic potential. The plastic area surrounding the opening has been analyzed by the coupling method of the boundaryelement method and the characteristics method, presented in the first report. To evaluate the elasto-plastic displacement in the plastic area, the method of characteristics has been successfully applied, and the Mohr-Coulomb's failure criterion is adopted for the plastic potential.
Hydrostatic pressure problem has been firstly discussed, and it is noted that the radial displacement at the inner surface of a circular opening is mainly depending upon the ratio of hydrostatic pressure to the uniaxial compressive strength of rock, and the influence of the coefficient of internal friction is comparatively small when the associated flow rule is applicable. Moreover, the present numerical analysis has been compared with the analytical solution and proved effective.
For the bi-axial stress condition that the ratio of initial principal stresses is greater than 1/3, it is made clear that the partial yielding around a circular opening proceeds to the yielding of whole surface with increase of initial stress. By analyzing the relationship among the intensity of initial stress, the depth of plastic area and the elasto-plastic displacement at the innersurface, it has been concluded that the maximum surface displacement due to the excavation is not affected very much by the ratio of initial principal stresses and can be evaluated from the analytical solution under hydrostatic pressure condition.