# Health State Assessment of Road Tunnel Based on Improved Extension Cloud Model
## 5 Conclusions  
To accurately evaluate the health status of road tunnels, a road tunnel health status evaluation method is proposed based on an improved extension cloud model. The main conclusions are as follows:  
1. The factors affecting the health status of road tunnels are complex, and the health status evaluation is a multi-index complex system. In this paper, eight static indicators and five dynamic indicators were selected from four aspects: tunnel lining, maintenance road, drainage system, and pavement. The dynamic indicator values were obtained by fitting the 5-year road tunnel disease data using the Cubic b-spline smoothing function. The dynamic and static evaluation system was set for road tunnel health status. The weights of evaluation indicators were determined based on the subjective and objective combination weighting method incorporating the AHP and improved entropy methods. The results showed that dynamic indicators can reflect the impact of changes in the health status of road tunnels on the evaluation results. 2. The randomness and fuzziness problems are solved at the boundary of levels in tunnel health status evaluation by improving the extension cloud model with the cloud entropy optimization algorithm. The extension cloud model is applied to the evaluation of the health status of road tunnels. The evaluation process of the road tunnel health status is set based on the improved extension cloud model. 3. The evaluation results were compared with the evaluation results of the current Chine code \"Technical Specification for Maintenance of Road Tunnels\" (JTG H12-2015). 80% of the evaluation results were consistent with the normative results, which verified the feasibility of the extension cloud model in the evaluation of the health status of road tunnels. 20% of the evaluation results had a higher level than the normative results, which reflects the evaluation results are impacted by the trend of tunnel health status changes. It indicates the necessity of considering dynamic indicators to set evaluation indicators. The credibility of the evaluation results was set by using the confidence factors test, and the confidence factors in the results were all less than 0.05. Theoretical and applied research is carried out by combining a case study, and the final evaluation results are consistent with the normative results. However, this method also has some shortcomings and limitations: disease indicators are still not detailed enough and the interaction between tunnel diseases is not considered. To evaluate the health status of highway tunnels more scientifically and accurately, the interaction between tunnel diseases can be considered based on incorporating dynamic indicators in future studies. In summary, the feasibility of the extension cloud model is verified in the evaluation of the health status of road tunnels. The framework for the evaluation of the road tunnel health status is set based on the improved extension cloud model. The proposed evaluation method based on the improved extension cloud model provides innovative ideas for the evaluation of the health status of road tunnels. This work can provide theoretical support for the scientific formulation of maintenance measures for road tunnels. Conceptualization, H.C., G.C., M.Z., Y.S. and J.L. ; data curation, G.C. and M.Z. ; resources, H.C. and G.C. ; investigation, H.C., G.C., Y.S. and J.L. ; methodology, H.C. and G.C., M.Z. and Y.S. ; software, J.L. ; visualization, Y.S. ; validation, G.C. and M.Z. ; writing--original draft, J.L. and Y.S. ; writing--review and editing, M.Z. and Y.S. ; supervision, H.C., G.C. and M.Z. ; formal analysis, H.C., G.C. and M.Z. ; funding acquisition, H.C. and M.Z. ; project administration, H.C., G.C. and M.Z. ; All authors have read and agreed to the published version of the manuscript. This research was funded by the National Natural Science Foundation of China, grant number 52172304, the Key Funding Project of Hebei Provincial Department of Science and Technology, grant number 22370801D. Not applicable.