<p>Concealed karst caves surrounding existing tunnels are widely distributed and can be rapidly replenished with water under heavy rainfall conditions, imposing severe challenges to the safe operation of underground engineering in karst regions due to excessive water pressure. To investigate the impact of concealed karst caves on tunnel water inrush during intense rainfall, this study constructs a simplified computational model for tunnel water inrush incorporating concealed karst caves under heavy rainfall scenarios, derives formulas for calculating tunnel inflow and cave recharge, and validates the model rationality and formula correctness via degeneration analysis. The results show that, for a given karst cave volume, tunnel inflow increases nonlinearly with the angle α between the cave and the tunnel. The sensitivity of angle α to tunnel inflow is relatively weak when the cave is located at the tunnel vault or invert (top or bottom of the arch), whereas it is maximized in horizontal positions. Additionally, cave recharge exhibits angle-dependent nonlinear growth as the distance between the concealed cave and the tunnel increases for a fixed cave volume. Both tunnel inflow and cave recharge decrease nonlinearly with increasing distance, and the influence of the angle on tunnel inflow weakens when the distance is constant. Given the complex effects of cave volume on tunnel inflow, this study recommends prioritizing the detection of concealed karst caves above the tunnel centerline and improving the detection accuracy for small-volume cavities.</p>