The topography in Japan is narrow and steep, so that there are some case when a large cutting and excavation of natural ground are carried out and a large slope of rock masses is eventually formed. Therefore, it seems to be a very important problem to investigate the slope stability on civil engineering. On the other hand, it is a common knowledge that the rock masses have bedding, Schistosity, joint and crack by weathering, or fractured zone and fault within slope. These become to form a discontinuous plane or a weak layer mechanically. For that reason, it is well known that the rock masses which has such characteristic show the anisotropic mechanical behaviour. Therefore, various reports have been given on the study of such rock masses. The analytical reports in their studies may be divided mainly two classes as follow:
the method taking account of the specified discontinuous plane (e.g. Goodman 1968).
the method inducing the properties of discontinuous plane to mechanics of continuous body (e.g. Iida 1972).
On the other hand, Kawamoto (1968), Hibino (1977) are to investigate directly the influence of anisotropy of rock masses on the basis of mechanics of elasticity of anisotropic body.
From the view points mentioned above, this paper treated the slope composed of anisotropic rock masses as a link of study (Kitahara 1979) about the problems of slope stability. That is, on the basis of theory of elasticity of anisotropic body, the method of numerical analysis considered with anisotropic mechanical properties and the characteristic of non-linear change of rock masses are developed here. Using the method, the behaviours at the time during the excavation of real slope composed of fractured zone and remarkable joints are forecasted and comparison with the results obtained by the method of isotropic analysis in the past are carried out. Moreover, comparison between the analytical forecast and the measured results from the viewpoint of safety execution of excavation are carried out, and the stability of real slope in the site and the appropriateness of the method developed here are examined.
The method applied is elasto-plastic analysis of the successive stress incremental procedure by FEM under the condition of two-dimensional plane strain and anisotropic mechanical properties of rock masses is introduced. In this paper, rock masses are regarded as cross-anisotropic materials.
Deformability of rock masses is assumed as follows:
Modulus of deformation (E1)and Poisson's ratio (V1) in the bedding plane, and modulus of deformation (E2)in the orientation perpendiculared to the bedding plane follow the numerical expressions independently. According to the principal of energy on theory of elasticity, the relationship between E1, E2, V1 and V2 is kept as V1/ E1 = V1 /E2. Where V2 is Poisson's ratio at the same direction as E2• In order to express numerically non-linear relation between stress and strain, an equation for modulus of deformation is represented as follows (Ito. 1981).