The surrounding rock is in the initial stress state before the tunnel excavation, and it undergoes the stress redistribution to reach the secondary stress state after the tunnel excavation. The surrounding rock is not only the main load source but also is an important part of the load bearing structure. Once the stress of some zone in the surrounding rock exceeds the strength of the rock mass, the part surrounding rock will enter into a state of plasticity or failure. Analytical solution is the most powerful mean to analyze this kind of underground cavern engineering problems. However, the existing solutions can not directly or simultaneously obtain the secondary stress field and excavation disturbance displacement field that we are concerned about. The implicit approximate solution cannot be degenerated to an accurate axisymmetric expression for the most existing non-axisymmetric elastic–plastic solutions. Therefore, this paper derives the elastic solution of a circular tunnel under the condition of the non-axisymmetric external load with the radial and shear inner loads. On this basis, the new elastic–plastic solution and the plastic zone radius equation of the circular tunnel under the conditions of the non-axisymmetric external load with radial inner load are derived. It can directly obtain the secondary stress field and excavation disturbance displacement field, and can degenerate to an accurate axisymmetric expression. The distribution characteristics of the analytical solution are in good agreement with the numerical test results, indicating that the new solution can provide a relatively accurate theoretical basis for the analysis and research of tunnel engineering.

Stability of surrounding rock mass and safety of supporting system in mining tunnel are always dominated by fault near excavation limit. The influence degree of the fault varies significantly under different fault distances to mining tunnel and initial stresses condition. In this paper, a series of numerical experiments are conducted to study the displacement, stress, and plastic region in surrounding rock mass. The stress characteristics in sprayed concrete layer are analyzed to study the influence of the fault distance on excavation limit and the initial stress in ground. The fault distance is defined geometrically by a mutual perpendicular line between the excavation limit and fault line nearest to the mining tunnel to quantify the influence. In order to simulate fault specialty reasonably, an interface model based on the theory of cohesive joint element is proposed in the numerical experiment model. Some other disciplinary and quantificational regularities about the influence of the fault distance and tectonic stress are summarized based on the numerical results. The results show that there is a critical distance to judge whether a fault has a prominent influence to mining tunnel. The critical distance depends on the quality of mining tunnel surrounding rock mass, initial stress, and the degree of excavation limit curvature. With the increase of lateral stress coefficient, the vertical displacement at crown decreases, but the horizontal displacement increases in the both right and left sidewalls.

The mechanical properties of joints are important factors affecting the safety and stability of rock mass. The joint roughness coefficient (JRC) is a parameter for describing the roughness morphology of the joint surface, and its accurate quantification is very important to predict the shear strength. In the current statistical parameter methods for the estimation of joint roughness, the size of different protrusions on the joint surface was completely ignored, which did not correspond to the real failure mechanism of rock joint during the shear process. In this study, a new statistical parameter WPA was proposed for the estimation of JRC considering the shear direction and the contributions of different protrusions. First, the 10 standard roughness joint profiles were digitized based on image processing technology, and the obtained coordinate data were proved to be reliable by the calculation results of existing parameters. Secondly, the WPA value of 10 standard roughness joint profiles was calculated at a 0.5 mm sampling interval in two directions. The functional relationship between WPA and JRC indicated that they should be established in the same shear direction to maintain a high correlation. The JRC values of 10 standard roughness joint profiles in direction 2 were obtained based on the functional relationship established between WPA and JRC in direction 1, and the roughness of these 10 joint profiles was confirmed to be influenced by direction. Next, the effect of sampling interval on WPA was investigated. As the sampling interval increases, the WPA values gradually decreased and the correlation between them and JRC gradually declined. In practical application, a smaller sampling interval was recommended for more accurate prediction. Finally, the geometric coordinate data of 21 joint profiles given in the literature and 4 natural joint surfaces were obtained by graphics processing technology and 3D scanning technology, respectively. The JRC values of them were separately estimated by WPA in different directions. The results showed that the new statistical parameter WPA proposed in this paper can well describe the joint roughness considering the shear direction and the contribution of different protrusions.

The non-Darcy seepage characteristics of broken rock mass is important for analyzing the seepage and stability of rock and soil mass. At present, the research on non-Darcy seepage models considering hydraulic conditions and medium void structures has considerable room for improvement. In this study, non-Darcy seepage tests were conducted on broken rock mass under the influence of different hydraulic pressures, sample gradations, and porosities. The influence of sample gradation and porosity on the linear and nonlinear term coefficients of Forchheimer’s law, the critical criterion of non-Darcy seepage, and the seepage flow regime was clarified. The influence of hydraulic gradient on the value of traditional hydraulic conductivity was revealed. A non-Darcy equivalent hydraulic conductivity, which changed with pressure gradient, was defined, then Forchheimer’s law and Darcy’s law were modified. Results showed that the relationship between pressure gradient and flow rate highly obeyed Forchheimer’s law. The minimum value of Forchheimer number was 9.4 times the critical value. Owing to the influence of inertial force and variable seepage channels, the linear and nonlinear term coefficients of Forchheimer’s law decreased while the Forchheimer number increased with the increase of pressure gradient, sample gradation, and porosity. With high hydraulic gradient, the non-Darcy equivalent hydraulic conductivity decreased nonlinearly, causing Darcy’s law to overestimate the seepage flow in this study by 2.47–13.40 times. Finally, Forchheimer’s law and Darcy’s law were modified to consider the influence of hydraulic gradient, sample gradation, and porosity. The modified Darcy’s law does not require the determination of the seepage flow regime and can accommodate the mutual transformation and coexistence between Darcy and non-Darcy seepage.

The joint roughness coefficient (JRC) is an important factor affecting the shear properties of rock joints, and its accurate estimation is a challenging task in rock engineering. Existing JRC evaluation approaches such as the empirical comparison method and the statistical parameter method have some unresolved defects. In this study, a new method is proposed for JRC estimation to overcome the deficiencies of existing approaches based on back calculation of shear strength. First, the 10 standard roughness joints are established in numerical rock samples generated by the bonded particle method (BPM). Secondly, the microscopic parameters of the intact rock and joints are calibrated, and a series of direct shear tests of joint samples are carried out under different normal stresses. Finally, the empirical relationships between shear strength and JRC are proposed under high correlation conditions. The results show that the modified smooth joint model (MSJM) is proved to better simulate the mechanical properties of rough joints than the smooth joint model (SJM). When the shear strength of target joint is substituted in the corresponding relationship, the JRC of joint along the shear direction can be conveniently obtained. In addition, the JRC values of 10 standard roughness joint profiles under shear direction of from right to left (FRTL) are obtained. By estimating the JRC of 9 target joints in the literature, it can be seen that the new method proposed in this paper can well reflect the directionality of roughness and it is convenient to apply.