A new constitutive model for the shear behavior of rough rock joints is proposed. Within the framework of the classical elasto-plastic theories, the model incorporates the dilation and surface degradation which are distinct features of rough rock joints, The elastic behavior is represented by the shear and normal stiffness. To calculate the plastic displacements after yielding, the nonassociatted flow rule is applied. Maksimovic's equation and Lee's empirical formula for joint shear strength are used for yield and plastic potential functions. The changes of the joint roughness angle that occurred in pre- and post-peak ranges of shear strength curve were approximated by simple power expressions of accumulated tangential plastic work. A discrete finite interface element, which has 6-node and zero thickness, was developed for implementing the proposed joint constitutive model. In order to evaluate the performance of the model, numerical direct shear tests were carried out. The results of the simulation confirmed that the proposed model could reproduce salient phenomena commonly observed in actual shear test or rock joints, including the shear strength hardening, softening, and dilation phenomena.


The shear strength of rock joints is greatly influenced by the roughness of joint surface. Due to surface undulation, the shear displacement along the joint is accompanied by the increase of the normal displacement. This dilation feature or rough rock joints may play an important role in stabilizing the rock mass in same situations. The constraint of normal deformation leads to the increase in normal stress, which in turn gives the mobilization of shear resistance against sliding. Moreover, the profile of joint surface is subjected to a continuous change during the slip. Therefore, a study to understand the complex behavior of rock blocks formed by a few dominant discontinuities intersecting the rock mass, should be equipped with a numerical model which can reproduce the dilatancy of real rock joints in a simple and effective manner. Considerable efforts have been devoted to explaining the relation between the peak shear strength and the surface topography of joints under compressive normal stresses. The shear strength criteria proposed by Pallone (1966), Ladanyi & Archambault(1970), and Barton & Choubey (1977) are good examples. These criteria, however, can only be used for the purpose of estimating the peak shear strength and thus failed to find their appilcations in describing the hardening and softening phenomena In the pre- and post-peak ranges of the shear displacement - shear stress curve. In 1976, Goodman attempted to make use or the complete normal and shear deformation curve individually in his numerical study of rock joints, but he failed to couple two curves. In 1987, Plesha proposed a more advanced constitutive model that can consider the wear of joint roughness. Plesha's model, however, still require more experimental validation. Based on the Maksimovic's formula for rock joints, this paper proposes an elasto-plastic constitutive model which can capture the pronounced deformation features revealed in the direct shear test.

This content is only available via PDF.
You can access this article if you purchase or spend a download.