The cracks and holes in underground engineering are the critical factors that cause the instability of the surrounding rock. It is helpful to control the stability of surrounding rock to study the samples with combined defects of cracks and holes. In this study, PFC 2D is used to analyze the numerical models. Seven combined models of single circular hole and double cracks with different angles are established, and the fracture angle varies from 0° to 90° with an interval of 15°. First, uniaxial compression experiments and numerical simulations are carried out in the 0° defect combination model, and the microscopic parameters of PFC 2D are determined. Then, the numerical simulations of seven defect models under uniaxial compression are carried out, and the crack development law and acoustic emission characteristics of different defect combination models are studied. The failure modes, mechanical behavior, and stress states are studied. The displacement vector distributions of different defect combination models are analyzed; it is found that there are three main types of macro cracks in the defect combination samples. The results show that the combined defects reduce the strength of the model. Meanwhile, the distributions of the stress and displacement are changed by the cracks with different angles in the defective models.

A closed-form analytical solution to rheological phenomena is obtained based on Hoek-Brown (HB) yield criterion and the generalized Bingham model. Once the circular tunnel is excavated, an initial plastic region is formed. When the total stresses fulfil the yield condition, the initial plastic region steps into the viscoplastic region, in which the displacement develops with time. The one-dimensional constitutive equation of the generalized Bingham model is transformed into a three-dimensional expression in polar coordinates by combining the plane strain condition. With the help of equilibrium differential equation, geometric equation and boundary condition, the stress and displacement in the initial plastic region can be expressed. At the moment of t, the stresses and displacements are described similar to the solutions of the elasto-plastic state. The stresses, strains and displacements after transformation can be expressed in the viscoplastic region. The proposed solution was verified by the closed-form solution of circular tunnels in elastic-brittle-plastic rock mass.

The mechanical and fracture behaviours of rocks are largely influenced by the rock structure and existing flaws. To study the effects of bedding and holes on the mechanical and microfracture behaviour of layered limestone, numerical specimens based on the cohesive zone model (CZM) method were first established. The cracks’ initiation, propagation and penetration processes during the entire loading process were used to reveal the fracture mechanism of numerical layered limestone under different conditions. The effects of bedding angle, hole location and hole number on the peak stress, failure pattern, length of total cracks and crack ratio of numerical layered limestone were then deeply studied. The numerical results indicate that the existing holes cause damage to the numerical layered limestone at different bedding angles. The hole has stronger and weaker damage influences on the peak stress at bedding angles = 0° and 30°. The hole location has different damage degrees on the peak stress at different bedding angles. The location and number of holes have no obvious influence on the failure pattern of numerical layered limestone at bedding angle = 60° and have a strong influence on the failure pattern of numerical layered limestone at bedding angle = 30°. Under most conditions, the length of total cracks is smaller than that of the intact numerical specimen. The location and number of holes have a strong influence on the ratio of tensile and shear cracks along the matrix for numerical specimens at bedding angles = 0°, 30° and 90°.