Grouting is a widely applied technique for reinforcing fractured zones in deep soft rock tunnels. By infiltrating rock fissures, slurry materials enhance structural integrity and improve the overall stability of the surrounding rock. The performance of grouting is primarily governed by the flow behavior and diffusion extent of the slurry. This review considers recent advances in the theory and methodology of slurry flow and diffusion in fractured rock. It examines commonly used grout materials, including cement-based, chemical, and composite formulations, each offering distinct advantages for specific geological conditions. The mechanisms of reinforcement vary significantly across materials, requiring tailored application strategies. The rheological properties of grouting slurries, particularly cement-based types, have been widely modeled using classical constitutive approaches. However, the influence of time- and space-dependent viscosity evolution on slurry behavior remains underexplored. Experimental studies have provided valuable insights into slurry diffusion, yet further research is needed to capture real-time behavior under multi-scale and multi-physics coupling conditions. Similarly, current numerical simulations are largely limited to two- and three-dimensional models of single-fracture flow. These models often neglect the complexity of fracture networks and geological heterogeneity, highlighting a need for more realistic and integrated simulation frameworks. Future research should focus on: (1) fine-scale modeling of slurry hydration and mechanical reinforcement processes; (2) cross-scale analysis of slurry flow under coupled thermal, hydraulic, and mechanical fields; and (3) development of real-time, three-dimensional dynamic simulation tools to capture the full grouting process. These efforts will strengthen the theoretical foundation and practical effectiveness of grouting in complex underground environments.

In tunnel construction in western China, a vast amount of carbonaceous slate is encountered. High in situ stress and foliation structures cause the rock mass to exhibit pronounced anisotropic creep, readily inducing a series of engineering disasters like collapses and lining cracks. Investigating the anisotropic time-dependent characteristics of carbonaceous slate is beneficial to the long-term stability of tunnel construction and operation. In view of this, carbonaceous slate specimens with different angles, β, between the foliation plane and loading direction were studied using a graded loading method through uniaxial compression creep tests. The results show that the instantaneous axial strain, ε_i, the axial creep strain, ε_c, the duration time of decelerating creep stage, t_d, and the steady creep strain rate, ${\dot{\epsilon }}_s$, increased with the rise in the loading ratio, k. Their variations followed a power law relationship, with the R² (Coefficient of Determination) values all exceeding 0.95. The value of ${\dot{\epsilon }}_s$ was observed to be less than 1.5 × 10⁻⁴/h when β < 45°, while it was found to exceed 1.5 × 10⁻⁴/h in the cases of $\beta \ge 45°$. The long-term strength, σ_L, of carbonaceous slate showed a U-shaped pattern with the variation in β. The maximum σ_L occurred at β = 90° and the minimum was observed at β = 15°. A fractional nonlinear creep model (FNC model) was developed. The sensitivity analysis reveals that the larger the fractional order n is, the t_d and ${\dot{\epsilon }}_s$ increase. η₂ and E₂ primarily affect the decelerated creep stage, while the ${\dot{\epsilon }}_s$ exhibits a rapid increase with the rise of η₁. To further validate the FNC model, a comparison is made with the traditional Nishihara model. The R² of the FNC model is larger than 0.965, which is higher than that of the Nishihara model (R² ≤ 0.911). The FNC model can effectively cope with the impact of the sudden increase in strain and well describe the characteristics of the decelerating, steady-state, and accelerating creep stages at any stress level and any angle. The results provide a reference for the study of the creep mechanism of layered rocks.

The accurate assessment of water inrush risks is crucial for tunnel safety in water-rich karst areas. This study introduces a risk assessment method based on a two-dimensional cloud model to address the associated uncertainties. A comprehensive risk indicator system is established, covering five principal factors: stratigraphic lithology, geological structure, topography, natural geography, and construction activities. The weights of these indicators are determined using an integrated Fuzzy Analytic Hierarchy Process and Entropy Weight Method. A two-dimensional cloud model is constructed, incorporating the dual dimensions of risk probability and loss severity. The risk level is then determined by analyzing the distribution of synthesized cloud droplets across predefined risk zones. Applied to the Andangnong Tunnel project, this methodology evaluates the water inrush risk as greater risk (Level II), a result consistent with the project’s dedicated safety assessment. Following the targeted treatment of key karst caves (Y5-2 and Y2-2), the risk level was successfully reduced to low risk (Level IV). This approach provides a scientific basis for risk management in similar geotechnical engineering contexts.