Evaluation Methods and Engineering Applications of Suitability for Water and Sand Inrush Treatment Schemes in Disintegrated Dolomite Tunnels

[Objective] During the construction of water-rich disintegrated dolomite tunnels, water and sand inrush disasters are prone to occur frequently, seriously affecting construction progress and project safety. [Methods] The Chenaju Tunnel of the Central Yunnan Water Diversion Project was taken as the research object. Considering the main factors affecting the suitability of water and sand inrush treatment schemes, and in combination with the characteristics of disintegrated dolomite strata and the formation mechanism of water and sand inrush, ten evaluation indicators were selected from four aspects: rock mass characteristics, groundwater conditions, tunnel length and burial depth, and the environmental impact of water and sand inrush. Key factors such as the disintegration degree of dolomite, unfavorable geological structures, external water pressure, and water richness were incorporated into the evaluation system, compensating for the insufficient consideration of disintegrated dolomite characteristics in existing evaluation systems. A suitability evaluation system for water and sand inrush treatment schemes applicable to disintegrated dolomite strata was established. A game theory-based combined weighting method was adopted to balance the weights calculated by the Analytic Hierarchy Process (AHP) and the CRITIC method, thereby improving the scientific rationality of weight allocation for evaluation indicators. The TOPSIS method was applied to rank the suitability of treatment schemes, and the suitability was classified into four levels: Grade Ⅰ (excellent), Grade Ⅱ (moderate), Grade Ⅲ (low), and Grade Ⅳ (poor). Combined with obstacle factor diagnosis, the key factors restricting suitability were quantified and identified. [Results] The results showed that, by comprehensively considering the main disaster-causing factors of water and sand inrush in disintegrated dolomite tunnels—such as the deterioration of rock mass characteristics, groundwater seepage and external water pressure driving effects, and the hydraulic channel effect of unfavorable geological structures—as well as engineering constraints including technical feasibility, economic efficiency, and treatment difficulty, the established evaluation system was able to accurately reflect the particularity of disintegrated dolomite strata, identify the main factors restricting the suitability of water and sand inrush treatment schemes in disintegrated dolomite tunnels, and produce evaluation results that were consistent with actual engineering conditions. [Conclusion] The key factors included in the evaluation system, such as the disintegration degree of dolomite, unfavorable geological structures, external water pressure, and water richness, fully reflect the characteristics of disintegrated dolomite rock masses, including low strength, poor self-stability, and high sensitivity to external disturbances, highlighting the complexity of water and sand inrush formation in disintegrated dolomite strata and its constraining effect on treatment schemes. When disintegrated dolomite tunnels pass through water-rich tunnel sections, the risk of water and sand inrush increases significantly. Under special unfavorable geological conditions, when disintegrated dolomite tunnels encounter high-frequency and large-scale water and sand inrush events, rerouting to avoid high-risk areas shows superior suitability.