<p>Climate change has led to an increased frequency of sustained and heavy rainfall events, imposing higher demands on the design and performance prediction of capillary barrier cover (CBC) regarding their hydraulic resistance. This paper proposes an explicit analytical model for predicting the failure time of CBC under heavy rainfall, which quantitatively accounts for the entire dynamic infiltration process from non-ponding to ponding conditions. The model incorporates the unsaturated dynamic characteristics of the wetting front and the hydraulic barrier effect at the fine-coarse soil interface. Based on the infiltration analysis, a water balance method is further introduced to enable real-time prediction of water storage and runoff in CBC. The results demonstrate that the model exhibits strong applicability in both vertical and inclined infiltration scenarios. It accurately predicts the failure time of CBC under heavy rainfall and, through the water balance predictions, provides further insight into water movement patterns within the cover system. The proposed computational model can provide support for the design of landfill covers and slope protection engineering under extreme rainfall conditions, offering a viable low-cost method to reduce the risk of CBC failure during the operational period.</p>