Evaluation of underground karst development state for tunnel construction by using the extension assessment method

The occurrence of karst-related disasters during tunnel construction is closely related to the underground karst development state (UKDS). Evaluation of UKDS before tunnel construction is essential for predicting and preventing karst-related disasters during tunnel construction. This paper presents a system to evaluate UKDS before tunnel construction by using an improved extension assessment method. Based on theoretical and case history statistical analyses, nine factors influencing karst development are selected as evaluation indices and are quantitatively graded. The weights of evaluation indices were determined by a comprehensive weighting method combining Hierarchy Analytic Process and correlation analysis. Correlation analysis was applied to obtain correlation degrees between evaluation indices and UKDS levels, and the maximum correlation degree principle was used to identify UKDS levels of the evaluation objectives. A characteristic variable value is calculated to distinguish differences between objects with the same UKDS levels. A case study demonstrates the application of the evaluation system. The evaluation results were generally consistent with conditions encountered during tunnel construction, indicating that the proposed UKDS evaluation system is effective. The advantages of the proposed UKDS evaluation system were also verified by comparison analysis. The UKDS evaluation system should aid in the early evaluation and prediction of karst conditions and help to prevent karst-related disasters during tunnel construction.