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This paper proposes an empirical equation to evaluate the shear strength of rock mass with nonpersistent joints. A novel specimen preparation method is proposed and is used to created plaster specimens containing nonpersistent joints. Utilizing the proposed method, it is possible to create specimens with nonpersistent closed joints with different roughness levels along different directions. The normal stress applied to embedded nonpersistent joints is the key factor for estimating the joint friction contribution to the shear strength of rock mass with the joints. An analytical equation and an experimental approach are proposed to calculate the normal stress applied to the nonpersistent joints. Seemingly good agreement was found between the normal stress values obtained using the analytical equation and those measured by the experimental approach. To study the effects of four influential parameters, namely rock bridge ratio, material strength, joint roughness, and normal stress, on the shear strength of specimens with a single nonpersistent joint, an experimental layout was designed based on the Taguchi method. The results of the extensive experimental work were then expressed in terms of an empirical equation to calculate the shear strength of specimens embedding a single nonpersistent joint. [ABSTRACT FROM AUTHOR]

The geometrical and mechanical properties of non-persistent joints as well as the mechanical behavior of intact rock (rock bridges) are significantly effective in the shear strength of weakness planes containing non-persistent joints. Therefore, comprehensive knowledge of the shear mechanism of both joints and rock bridges is required to assess the shear strength of the planes. In this study, the shear behavior of specimens containing a single non-persistent rough joint is investigated. A novel procedure was used to prepare cast specimens embedding a non-persistent (disc-shaped) rough joint using 3D printing and casting technology, and the shear strength of the specimens was examined through an extensive direct shear testing program under constant normal load (CNL) condition. Three levels for three different variables of the joint roughness, rock bridge ratio, and normal stress were considered, and the effects of these factors on the shear behavior of prepared samples were tested. The experimental results show a clear influence of the three variables on the shear strength of the specimens. The results show that the normal stress applied to the jointed zone of weakness planes is considerable, and thus joint friction contribution should be taken into account during shear strength evaluation. Furthermore, the dilation mechanism of the specimens before and after failure was investigated through a digital image correlation analysis. Finally, a camcorder was used to analyze the location and sequence of the initiated cracks. [ABSTRACT FROM AUTHOR]