[PERSON] et al. [11] proposed a mathematical model of the discrete joint network unsaturated seepage problem based on the discrete joint network model, whose proposed algorithm plays an important role in solving the reliability of the rain infiltration problem of the fractured slope. In a fracture structure characterization and mechanical characteristics research, [PERSON] et al. [12] used the DFN model to discuss the stability calculation of fractured rock masses based on the Voronoi model, Baecher model, and Veneziano model, whose research results provided a new idea for the stability evaluation of fractured rock masses. Further, the DFN model has been widely used in fields, such as slopes [13] and tunnels [14]. The DFN model could also be used to estimate the block volume distribution using the persistent discontinuities [15]. [PERSON] et al. [16] discussed the DFN modelling method based on drillholes and investigated the influence on the excavation damaged zone. Whether in the two-dimensional or three-dimensional discrete joint network model, most of the numerical simulation analysis and research on rock joints assume that the rock mass structural plane is a plane, and the joint section is a straight line. However, the structural surface of the rock mass is a rough surface with unevenness instead of a complete and smooth surface in engineering practice, as shown in Figure 1. Further, the internal structural surfaces of rock masses in different scales (e.g., fractures, bedding planes, joints, and folds) have a certain degree of roughness. According to [17], the roughness of the joint surface will closely affect the propagation of the wave speed when studying the law of wave speed change. [PERSON] et al. [21] also revealed that the elastic wave velocity changes in rock samples with different joint roughness under cyclic loading and unloading. These studies proved that the roughness of rock mass joints is real and has an important influence on the properties of rock masses. Therefore, the roughness of the joint surface must be considered when studying rock mass. The joint roughness coefficient (JRC) was first proposed by [22] to express the roughness of the joint. Subsequently, many scholars performed several assessments to quantitatively evaluate the JRC value and the shape of the structural joint section. [PERSON] et al. [23] evaluated the JRC method of JRC based on the fractal principle. [PERSON] and [PERSON] [24] developed a fractal estimation method for JRC. [PERSON] et al. [25] used a random function with normal distribution to construct the joint section shape. [PERSON] et al. [26] analysed and reconstructed the rock joint morphology based on the discrete Fourier transform principle. Owing to further research on JRC by many scholars, the rock mass shear test on the characteristics of the joint surface roughness has been conducted. [PERSON] et al. [27], assumed that the rock mass structural surface had a regular tooth shape, conducted a shear test to explore the mechanical characteristics of the tooth structural surface, and established an empirical formula for evaluating the shear strength of the structural surface. [PERSON] et al. [28] discussed the influence of normal stiffness, initial normal stress, and structural surface roughness on the shear mechanical properties of structural surfaces. [PERSON] et al. [29] simulated and studied the shear behaviour of rough basalt fracture under constant and dynamic normal load conditions at different shear rates, and then proposed a new shear criterion to evaluate  
Figure 1: The roughness of natural discontinuities in fractured rock masses. (**a**) The micro fracture [17]. (**b**) Bedding planes [18]. (**c**) The step-path surface at the Aishihik River Landslide [19]. (**d**) The macro fold [20]. the shear behaviour of rough joints under this condition. The findings of these studies revealed that the surface roughness of joints is the most important factor affecting the mechanical properties of rock masses, such as strength and deformation.