Generally speaking, actual foundation is inhomogeneous in mechanical properties and discontinuous in structure, and therefore it is desperately needed to make clear the characteristics of jointed rock media having such discontinuity.
A great number of studies have been made on the jointed rock media, which include the studies of the shearing strength or deformation characteristics, the biaxial or triaxial tests on jointed rock, and the studies of the stress transfer mechanism of jointed rock media.
The analysis of such jointed rock media is, however, still incomplete and these studies are not beyond qualitative discussion.
The method of numerical analysis for the foundation having the discontinuous properties are generally classified into the following two groups.
The finite element method with the use of joint elements.
Discrete method where rigid elements are considered.
The Goodman, Tayler εBrekke's method of the joint elements (1968) is only useful when the discontinuous surface is already known, and it is not possible to study the slip failure of foundation structures generally.
Kawamoto & Takeda(l978) proposed a similar method where crack elements are introduced. Their method, however, can be deduced from the Goodman et al 's jointed element method.
In contrast to these method, Cundall (1971) developed a method in which the foundation is idealized as an aggregate of completely discrete rigid elements, and he showed effectiveness in the analysis of a toppling failure of rocks. But the application is 1imited to analysisof a very shallow part of foundations. Independently in 1976 Kawai proposed a family of new discrete models which are called as the Rigid Body Spring Model (abbreviated as RBSM) by basing on the experimental evidance of sol ids under the ultimate state of loading. These models consists of rigid bodies and two types of connection springs, one of which resists the dilational motion, while the other the shear deformation. He conducted verification studies of his models by solving a series of collapse problems of the beam, plate, shell and three dimensional structures.
They were proved to be very effective for the analysis of the materials having the yield criterion of Mohr-Coulomb's type because only the normal and shearing stresses are necessary to consider on the element boundary.
Takeuchi (1980) attempted application of the RBSM models to no-tension analysis of the granular media which was originally proposed by Zienkiewicz (1968) and later by adding a scheme for checking on the contact of adjoining elements, he modified his program of the no-tension analysis and he called it the method of tension-crack analysis. Combined use of this method with the conventional elasto-plastic analysis, however, has not been attempted yet.
In this paper, therefore, considering the effect of re-contact as well as separation of individual rock elements, the elasto-plastic analysis was carried out by basing on the intial stress method by Zienkiewicz, Valliappan & King (1969).
