Accurate prediction of tunnel water inflow in water-rich fault zones is important for groundwater control design and construction risk prevention. In this study, a per-linear-meter tunnel water inflow database containing 425 valid samples was established through orthogonal numerical simulations based on a three-dimensional steady-state seepage model with a grouting ring. The input variables included four hydraulic and grouting parameters and two excavation-position descriptors, namely the excavation-position distance and excavation-position category, thereby reflecting both the water-blocking effect of grouting reinforcement and the spatial variation in water inflow as the excavation face approached the fault zone. Considering that the samples were generated from 25 orthogonal simulation cases at different excavation positions, grouped validation was adopted to reduce information leakage at the simulation-case level. Four baseline machine learning models, including SVM, RF, XGBoost, and CatBoost, were evaluated using ten repeated grouped hold-out validations. CatBoost achieved the best overall baseline generalization performance, with an average test R² of 0.6209 ± 0.0405, MAE of 0.1084 ± 0.0079, and RMSE of 0.1555 ± 0.0085. CatBoost was therefore selected for further hyperparameter optimization. Subsequently, random search, Bayesian optimization, the Osprey Optimization Algorithm, and the Grey Wolf Optimizer were compared under the same search space and computational budget. Hyperparameter optimization was conducted only within the training set using grouped cross-validation, and the independent grouped test set was used only for final evaluation. The results showed that the unoptimized CatBoost model achieved the best overall balance between prediction accuracy, stability, and computational efficiency. Although RS-CatBoost slightly improved MAE and MAPE among the optimized models, none of the optimization strategies consistently outperformed the unoptimized CatBoost baseline, indicating that the choice of hyperparameter optimization algorithm played a secondary role under the current dataset and grouped-validation framework. The proposed framework is intended as a preliminary modeling reference under controlled numerical simulation conditions, and its practical engineering reliability requires further validation using field monitoring data or independent benchmark cases.

Fault fracture zones can act as preferential groundwater flow paths and significantly modify the seepage field around tunnels. To investigate the influence of the fault–tunnel intersection angle on pore water pressure distribution in tunnel surrounding rock, a three-dimensional steady-state Darcy seepage model was established using the F4 fault section of the Yinggeling Tunnel as a representative engineering background. Four cases were considered: a fault-free tunnel and tunnels intersecting fault fracture zones at fault–tunnel intersection angles of 45°, 90°, and 135°. Pore water pressures were extracted at the tunnel crown, invert, and left and right sidewalls at radial distances of 0.2 m and 10 m from the excavation boundary to characterize the near-field and intermediate-to-far-field responses. The results show that the fault fracture zone acts as a preferential drainage pathway and reduces the pore water pressure around the tunnel. Under the baseline permeability condition, the 90° intersection case produces the strongest pressure-relief effect, with peak pore pressure reduction ratios of 23.66–24.24%, followed by the 45° case with reductions of 20.54–22.22%, whereas the 135° case shows a weaker reduction of 4.74–5.36%. Sensitivity analysis indicates that the 90° case generally maintains the strongest pressure-relief effect under most fault-to-rock permeability ratios, although the differences among some intersection-angle cases decrease at high permeability ratios. The near-field surrounding rock exhibits rapid pressure dissipation controlled by tunnel drainage and fault-guided flow, whereas the intermediate-to-far field shows a smoother and more attenuated response. These findings clarify the seepage-control mechanism of the fault–tunnel intersection angle and provide a reference for waterproofing and drainage design in tunnels crossing fault fracture zones.