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Rock mass usually have cracks and joints, and can be considered anisotropic. Many numerical and experimental studies have been made on the mechanical properties. However the method of numerical analysis which can fully express the behaviour of such anisotropic rock mass with such discontinuities has not yet been developed. Recently the necessity of large scale excurvations and consequently establishment of an effective method of analysis is considered urgent to clarify the mechanical properties of jointed and cracked rock media.This paper is based on the “rigid body spring models” proposed by Kawai, in which the elements themselves are assumed to be rigid and they are connected by two types of springs distributed over their interfase boundaries. Using the Mohr-Coulomb's failure criterion and considering the effect of contact as well as separation on the two points of interface boundaries of each elements, the perfect elasto-plastic analysis was carried out basing on the initial stress method.In this paper the following results were obtained.(1) Homogeneous and anisotropic mechanical characteristics of materials can be obtained by random or anisotropic discretization.(2) In some cases of cracked rock masses, the crack propagates by slow stable fracture, while such as in splitting tensile test, it causes an instantaneous unstable fracture. This two modes of fracture are verified by numerical analysis.(3) Fracture pattern results for jointed rock are good agreement with experimental and numerical results.

Stress transfer mechanism of the jointed rock media was studied theoretically and experimentally. The discrete element model used in this study is based on the “rigid body-spring models” proposed by the second author, Kawai five years ago. In these models it is assumed that the elements themselves are rigid and they are connected by two types of springs distributed over their interface boundaries.Using the well known Mohr-Coulomb's failure criterion and considering the effect of contact as well as separation of individual rock elements, the elasto-plastic analysis was carried out by basing on the initial stress method. It was found that the calculated results were in fairly good agreement with the results of the photoelastic analysis and that the stress distribution of these jointed rock media was considerably different from that of the compressed homogeneous continuous media.

The mechanical properties of the rock masses are influenced by existence of joints and faults. Especially roughness of the discontinuous surfaces determine the strength-deformation characteristics of rock masses.Barton indicated the influence of the JRC (Joints Roughness Coefficient) for the arbitrary shaped asperities upon the shear strength, shear stiffness and normal stiffness. However, the Barton's shear strength criteria is only applicable to a domain of comparatively small confining pressure where does not get the asperities sheared. off. Ladanyi & Archambault developed a shear strength criteria for the asperities under the shear off condition. This criteria can take account of progressive failure when the asperities leave the initial condition of complete interlocking. The criteria, however, can be only applicable to the case of regular shaped asperities. In order to apply this criteria to analysis of the shear strength of actual rock mass, it is necessary to convert the irregular shape into a regular one.This study is based on a consideration of the applicability of the Barton's joint roughness as well as Ladanyi & Archambault's shear strength criteria and deals with a transformation of the irregular shaped asperities into a regular one in a discontinuous surfaces.

In this paper experimental as well as numerical results are reported for stress distribution in jointed rock media having various types of discontinuities, and these are compared with the corresponding results for a homogeneous elastic media.When the angle θ between the joint surface and horizontal axis of cohesionless jointed rock media is varied in the range 0