Assessment of a Concealed Karst Cave’s Influence on Karst Tunnel Stability: A Case Study of the Huaguoshan Tunnel, China

In order to assess a concealed karst cave’s influence on karst tunnel stability, an assessment model is proposed based on the analytic hierarchy process and a statistical analysis of relevant engineering projects. Major factors are studied and selected as impact factors of the assessment model based on a statistical analysis on a karst cave’ s development conditions (karst hydrogeological and engineering geological conditions), construction conditions, and controlling measures. A weight analysis of factors shows that the surrounding rock grade, supporting measurement, formation lithology, unfavorable geology, construction methods, blasting techniques, advanced geological forecast, and groundwater level are the main controlling factors of the tunnel stability when there is a concealed karst cave in the tunnel. Topography and geomorphology, attitude of rocks, monitoring measurement, strata combination, and interlayer fissures are the minor influence factors. Tunnel section shapes, in situ stress, and geological logging are the least important factors. The proposed method is successfully applied to the assessment of a concealed karst cave’s influence on the stability of the Huaguoshan Tunnel on the Enshi-Laifeng and Enshi-Qianjiang Expressways. The evaluation result agrees well with the construction site situation. In addition, the result provides good guidance with respect to the implementation of the treatment scheme and effectively avoids accidents in real-time