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Water inrush hazards are a significant geological risk in the construction of deep-buried karst tunnels, directly impacting the safety and quality of engineering projects. This study aims to address the risk of water inrush during tunnel construction in areas with abundant water and deep-buried karst formations. Using a water-rich deep-buried karst tunnel from a proposed highway in Guangxi as a case study, we conducted a systematic analysis of the region's hydrogeological characteristics through geological surveys. This analysis covered the occurrence and migration patterns of groundwater, as well as the main factors influencing water inrush in karst tunnels. These factors include stratigraphy, geological structures, topography, and hydrogeological conditions.To evaluate the risk of water inrush, we established a risk assessment system based on a combination of the Combined Weighting-TOPSIS method. This system takes into account various factors influencing water inrush and employs the Analytic Hierarchy Process (AHP) and the Entropy Weight Method to determine the weights of these factors. By calculating the combined weight with the TOPSIS method, we obtained the distance and relative closeness between typical tunnel sections and the ideal solution, allowing us to evaluate the water inrush risk across different tunnel sections. The results indicate that this method demonstrates high accuracy and feasibility in actual tunnel excavation. The application of this risk assessment system provides an effective tool for evaluating water inrush risks in tunnel construction, contributing to enhanced safety and construction efficiency.