By using the three-dimensional discrete element method (DEM), the effect of micro parameters of smooth joint on macro properties of a jointed rock sample is investigated. A series of triaxial compression tests are simulated to obtain its pre-peak properties, which are influenced by the parameters of smooth joint including friction coefficient, normal stiffness, and shear stiffness. The friction coefficient is found to have the most significant impact on the macro properties including yield strength, Young's modulus, and Poisson's ratio. A reduction in friction coefficient significantly decreases the strength and changes the pattern of stress-strain curve. The stiffness of smooth joint has a relative small influence on the macro properties. The variation of stiffness does not change the pattern of stress-strain curve, and the normal stiffness has a more obvious influence on the macro properties than shear stiffness. Further analyses from the micro perspective are conducted by looking at the contact force, the distribution of different types of micro cracks, and the particle displacement to show the failure modes due to the variation of friction coefficient. The reduction of friction coefficient results in the change of failure mode from splitting to sliding.


The mechanical and geometric properties of joints are recognized as the key factors controlling the strength, deformability and stability of a rock mass, since typical joints are much softer and weaker than their surrounding intact rock material. The presence of joints, which is inherent and one of the most challenging problems to be solved, makes the design and construction of engineering structures complex and difficult. Therefore, many attempts have been made to characterize the properties of joints and evaluate their influence on the mechanical behavior of rock masses.

Numerous studies using artificial material for a rock mass with limited joint sets have been carried out by Hayashi [1], Brown [2], Einstein et al. [3], Einstein and Hirschfeld [4], Ramamurthy and Arora [5], and Yang et al. [6] to investigate the influence of joint sets, joint number, or joint orientations on the strength and deformational response of jointed rocks and failure modes. Many other investigators performed compression test on various anisotropic rocks, e.g. Attewell and Sandford [7] on slates, Niandou et al. [8] and Ambrose et al. [9] on shales, Al-Harthi [10] on sandstones, and Nasseri et al. [11] on schists, which generally revealed the variation of failure strength versus anisotropic angle characterized by a U-shaped curve [12]. Although these studies achieved a large number of valuable results, knowledge about the influence of mechanical properties of joints including joint stiffness, and joint friction on rock mass remains lacking.

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