In order to explore the influences of fault dislocations on tunnel stability under seismic action, a nonlinear dynamic simulation method for the rock–fault contact system is proposed. First, considering the deterioration effect of seismic action on the ultimate bearing load of the contact interface between rock mass and fault, a mathematical model is established reflecting the seismic deterioration laws of the contact interface. Then, based on the traditional point-to-point contact type in a geometric mesh, a point-to-surface contact type is also considered, and an improved dynamic contact force method is established, which considers the large sliding characteristics of the contact interface. According to the proposed method, a dynamic finite element calculation for the flow of the rock–fault contact system is designed, and the accuracy of the method is verified by taking a sliding elastic block as an example. Finally, a three-dimensional (3D) calculation model for a deep tunnel through a normal fault is built, and the nonlinear seismic damage characteristics of the tunnel under horizontal seismic action are studied. The results indicate that the relative dislocation between the rock mass and the fault is the main factor that results in lining damage and destruction. The seismic calculation results for the tunnel considering the dynamic interaction between the rock mass and the fault can more objectively reflect the seismic response characteristics of practical engineering. In addition, the influences of different fault thicknesses and dip angles on the seismic response of the tunnel are discussed. This work provides effective technical support for seismic fortification in a tunnel through fault.

In order to explore the influence of internal water on the seismic response of hydraulic tunnel, the combined mechanical analysis models of multimaterial including surrounding rock, lining structure, and internal water are built. Based on the explicit central difference method, the dynamic finite element analysis methods for rock, lining, and water are discussed, respectively. The dynamic contact force method is used to simulate the rock-lining contact interaction, and the arbitrary Lagrange-Euler (ALE) method is used to simulate the lining-water coupling interaction. Then a numerical simulation analysis method for combined seismic response of rock-lining-water system in hydraulic tunnel is proposed, and the detailed solving steps are given. This method is used to study the seismic stability characteristics of the water diversion tunnel in a hydropower station, and the displacement, stress, and damage failure characteristics of the lining structure under the conditions of no water, static water, and dynamic water are comparatively analyzed. The results show that the hydrostatic pressure restricts the seismic response of the lining, while the hydrodynamic pressure exacerbates its seismic response and leads to damage, separation, and slip failure appearing on the haunch, which can provide a scientific reference for the seismic design of hydraulic tunnel with high water head and large diameter.

At present, much attention has been paid to the ecology, economics, and social benefits of erosion control projects: however, the evaluation of an erosion control technology itself has been neglected. This study selected six soil conservation measures applied to the Loess Plateau, and a comprehensive evaluation model was developed considering the maturity of the technology, application difficulty of the technology, technology efficiency, and the potential of technology promotion. The relation between a condition attribute and a decision attribute is evaluated using rough set theory, and the decision attribute is completely dependent on the condition attribute, which indicates that the index system can better evaluate the soil conservation measures applied to the Loess Plateau. Rough set theory was used to determine the weights of evaluation indexes, which overcomes the limitation of relying only on expert opinions or index data to determine the weights. According to the comprehensive scores, the six soil conservation measures can be grouped into three levels: the first level includes economic forests, check dams, and terraces; the second level includes afforestation and conversion to grassland, and the third level includes enclosures. The results can provide a scientific basis for the promotion and application of the high-ranking soil conservation measures in the Loess Plateau. However, the comprehensive evaluation of the soil conservation measures applied to the Loess Plateau is a very complex problem. To maximize the eco-environmental benefits, land use patterns should be rationally adjusted, and corresponding soil conservation measures could be suitable for meeting the regional development goals.