線形ひずみ軟化特性を有する岩盤の構成方程式と円孔の軸対称問題

抄録

This paper describes a constitutive equation of rock which undergoes strain-softening deformation beyond its strength failure. The equation consists of stress-strain relations in elastic, strain-softening and residual strength regions. The stress-strain relation in strain-softening region was idealized to be linear and expressed in terms of a few parameters that are related to postfailure characteristics and fracture criterion of rock. For an illustrative example was demonstrated an analytical solution of displacement and stress around a circular hole under hydrostatic pressure. The solution shows that three annuli which correspond to elastic, plastic and flow regions, will be formed around it if hydrostatic pressure exceeds a critical value. The plastic zone is decayed with increase of the negative slope in the post-failure region, and ceases to exist as the negative slope gets infinitive. Both the radii of elastic-plastic and plastic-flow boundaries are given by analytical formulae. The formula for elastic-plastic boundary is reduced to one of the elastic-perfectly plastic model when the negative slope gets flat. while it is coincident with one of the elastic-flow model when the negative slope gets infinitive. The formula also suggests that the raidius of elastic-plastic boundary is much greater than that predicted by elastic-perfectly plastic model. This implys that the formula allows us to estimate a rational elastic-plastic boundary for a circular tunnel in rock or a relief boring in coal seam.