斜面崩壊機構の力学的分類

Abstract

In sloping layer stretched infinitely, it could not be determined theoretically where the for-mation of slip surface is initiated according to Mohr-Coulomb's law for the failure of soil, becauseof the indefiniteness of longitudinal distribution of stresses exerted in this layer. Then, the authorscontrived to derive two kinds of model slopes with the typical boundary conditions at the upper aridlower ends of slopes. The one, which was called T(tensile)-type, was provided for the constant dis-placement u0, at the upper end and for the constant normal stress σ0 at the lower one, and theother, whick was called C (compressional)-type, was provided for the reverse case.We considered the variations of average displacement ⊿u and average stress ⊿σx over the entiredepth of layer deviated from the equilibrium state of slope, taking up the example cases where theresistant force acting on bed rock surface was decreased and the deformation of soil was governedby rheological character of Voigt's osodel, and it was found that, in T-type model, ⊿σx was resultedin negative and the deformation was taken as the recovery expansion to lower compressional stateand the possibility of active failure would be expected in the upper region of slope, and that, inC-type model, ⊿σx was resulted in possitive and the deformation was regarded as the more contrac-tion to higher compressional state and the possibility of passive failure would be expected in thelower region of slope.The connection of upper end of C-type model to lower end of T-type one will form the slopelayer protected by retaining walls at both ends. The connection of upper end of T-type modelto lower end of C-type one will represent the mountain slope extending upwards from its toe wherethe bed rock surface is exposed by lateral erosion of stream, to the top where the slope possesses thecondition ∂⊿u/∂x owing to the symmetry of its deformation. On the basis of results obtained inabove, we derived the method by which the positions of occurrence of active and passive failureswere decided in the slope of T + C type, and also, discussed the condition under which the bottomlayer laid on bed rock surface was broken down in the slope of C + T type, referring to the knowledgefor the peak and residual strengthes of soil at shear deformation.