To analyze in-service tunnel structure safety, the coupling effect of a multi-factor should be considered. The karst highway tunnel structure safety is classified into five grades based on a railway tunnel health evaluation model. The factors affecting tunnel structure safety are addressed using an analytic hierarchy process. Qualitative indices are classified into five levels according to tunnel safety. A membership function that follows the Gaussian distribution is applied to determine quantitative evaluation indices. Those factors are assigned weights by expert scoring method of system theory, and the treated karst caves are set up as an uncompacted backfill model. A three-grade fuzzy comprehensive evaluation model is finally built for in-service highway tunnel structure safety in the karst area. The safety of Hui-long-shan tunnel is evaluated, and the safety value is judged by the maximum membership law according to the proposed model.

Following tunnel excavation, which is influenced by hydraulic fracturing and geological structure, a series of hydrochemical reactions occur in the karst aquifer, which has a significant impact on groundwater hydrology and the earth process. Based on five sets of 38 samples collected in the Tongzi Tunnel in 2020 and 2021, the main geochemical processes and water quality conditions of the karst aquifer system during tunnel construction were revealed by multivariate statistical analysis and graphical methods. The results showed that water-rock action is the main mechanism controlling groundwater chemistry in the study area; HCO₃^-, Ca²⁺, and Mg²⁺ are associated with the widely distributed carbonate rocks in the study area. SO₄^2- is derived from gypsum and sulfate rocks and special strata, which are another important source of Ca²⁺. Sodium-containing silicates and reverse cation exchange as the causal mechanisms of Na⁺ whereas F^- is derived from fluorite. According to the mineral saturation index calculations, the dissolution and precipitation of minerals such as alum, gypsum, calcite, dolomite, and salt rock have an important influence on the main chemical components in water. The 38 samples were subjected to cluster analysis, and the results could be classified into seven categories. The representative clusters 1, 3, and 5 were selected for principal component analysis. Clusters 1 and 5 of groundwater represent weathering, dissolution, and ion exchange of carbonate and sulfate rocks and are closely related to the lithologic limestone, limestone intercalated with carbonaceous mudstone, carbonaceous mudstone, and coal-measure strata in the aquifer. Cluster 3 is dominated by upper surface river water and characterizes the geochemistry in natural water bodies dominated by the dissolution of carbonate, sulfate, and salt rocks. Finally, groundwater quality is mostly found in Class IV, with NO₃^- and F^- being the main contaminants in the water.

In this study, cement mortar was used to make specimens containing groups of parallel joints with different inclination angles to simulate natural rock mass, and the specimens were subjected to shear tests under different normal stresses. By analyzing the crack propagation path, failure modes, and strength characteristics of these rock specimens, the effects of normal stress and joint inclination angles on the strength and failure characteristics of this type of rock mass were studied. The following conclusions are drawn: 1) when the inclination angles of the joints are 0° and 15°, the changing of the normal stress did not affect the failure mode of the rock mass. The rock mass was mainly in the mode of shear failure, and the increase in the normal stress only increased the spalling area of the rock mass. 2) When the inclination angles of the joints are 30°, 45°, and 60°, with the increasing of the normal stress, the number of those approximately parallel cracks in the specimens increased, the friction marks caused by shearing increased, and the failure mode of the rock mass changed from tension failure to tension–shear composite failure. 3) Under different joint inclination angles, the propagation and penetration paths of cracks generated in the rock mass and the damage mode of the rock mass were different. With an increase in the joint inclination angles, the damage mode of the rock mass gradually changes from shear damage to tensile–shear composite damage and the α and β angles between the through cracks and the vertical direction on the left and right sides of the specimens tended to decrease. 4) The shear resistance of the rock mass was affected by the inclination angle of the joints and the normal pressure. The shear resistance of rock mass was improved due to the increasing of normal stress. Within a certain range, with the increasing of the inclination angles of the joint, the shear resistance of the rock mass tended to decrease first and then to increase.

The double sidewall guide pit and centre cross diagram (CRD) methods are often used for the construction of large-section tunnels through water-rich fault fracture zones due to their long construction time and high construction cost. To shorten the construction period and save costs, the top heading and benching method (HB) and centre diaphragm (CD) can be chosen for construction. The construction parameters of the step and CD methods are optimized to ensure the surrounding rock stability and tunnel safety. By relying on the Tongzi Tunnel, we simulate the excavation of different step heights in the construction of the top heading and benching method (HB) and CD methods through numerical simulation, the laws of tunnel vault settlement, and changes in the surrounding rock stress, initial support axial force, bending moment and safety factor. The study shows that as the height of the upper step increases, the settlement of the vault and the convergence of the periphery increase, the initial support safety factor decreases, and the plastic zone of the surrounding rock increases at 30 m from the target face. The step height for the top heading and benching method (HB) of construction is optimized as follows. The ratios of the upper, middle and lower step heights are 0.45H, 0.35H and 0.2H, respectively. The CD method construction step height is optimized to the left (right) upper and left (right) lower step height ratios of 0.5H and 0.5H, respectively.

The mechanical property of jointed rock mass is an important factor to be considered in the analysis, evaluation, and design of actual rock engineering. The existence of joints threatens the stability and safety of underground engineering projects built in the rock mass. In order to study the change of mechanical properties and strength characteristics of nonpenetrating jointed rock mass under different test conditions, direct shear tests and triaxial tests were carried out. Direct shear tests under different normal stresses were carried out for nonpenetrating jointed rock mass to prepare specimens for triaxial tests. Then, triaxial tests were carried out to study the change of mechanical properties and strength characteristics of the nonpenetrating jointed rock mass. In the direct shear test part, the greater the normal stress is, the stronger the shear strength and the more serious the shear failure would be. The main conclusions are as follows: (1) the strength of rock mass would increase with the increase of confining pressure for those rock specimens with same degrees of shear after the direct shear test; (2) for rock specimens with different degrees of shear after the direct shear test, if the shearing degree of the rock specimen was greater, the strength of the rock specimen would be lower in the triaxial test; (3) for rock specimens with the same damage degree after direct shear test, the greater the normal stress in direct shear test is, the smaller the peak axial pressure would be in the triaxial test; (4) if the specimen was sheared under higher normal stress in direct shear test, the cohesion of it would be lower and the internal friction angle would be larger. For the specimens under the same normal stress, if the shear failure of one specimen was more serious, the cohesion of it would be smaller and the internal friction angle would be larger.