# Suitability Evaluation of the Lining Form Based on Combination Weighting-Set Pair Analysis
## 5 Discussion  
(1) Based on the example of the lining form of high-pressure pipelines in PSPS and combining the C-OWA operator, CRITIC method, improved EWM theory, and SPA theory, a new suitability evaluation method is proposed. Compared with the traditional evaluation methods, the advantages of this method are summarized as follows: (1) The combination weighting method consisting of subjective weight and objective weight can effectively avoid the error caused by a single weight method and make the prediction result closer to the actual situation. (2) The case study shows that the multivariate connection degree model is reliable and can be accepted for evaluating the reinforced concrete lining forms suitability and conveniently for practical applications. In addition, the connection degree indicates the interconnection and mutual influence of each index, and can represent the certainty and uncertainty degree from a whole perspective view, and the identical-discrepancy-contrary relationships between the sample and the classification grade. (3) In the selection of evaluation indices, the RQD index, which conventionally characterizes the structural features of rock mass, is improved and supplemented. The RBI index is used to replace RQD, so that the results can more accurately reflect the size of the rock mass, which has obvious engineering practical significance for the quantitative analysis of the variation characteristics of physical and mechanical parameters of rock mass.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Working Point** & **1** & **2** & **3** & **4** & **5** & **6** & **7** \\ \hline \(a\) & 0.5243 & 0.7162 & 0.7162 & 0.5243 & 0.5222 & 0.5842 & 0.5243 \\ \(b\) & 0.3051 & 0.0000 & 0.0000 & 0.0000 & 0.0620 & 0.0000 & 0.0000 \\ \(c\) & 0.1706 & 0.2710 & 0.2710 & 0.3315 & 0.0000 & 0.0000 & 0.0045 \\ \(d\) & 0.0000 & 0.0129 & 0.0129 & 0.1442 & 0.2168 & 0.0000 & 0.1873 \\ \(e\) & 0.0000 & 0.0000 & 0.0000 & 0.0000 & 0.1990 & 0.4158 & 0.2838 \\ \(\mu\) & 0.6769 & 0.7097 & 0.7097 & 0.4522 & 0.2457 & 0.1683 & 0.1468 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Five-element Connection Degree of Comprehensive Evaluation of Each Working Point.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Working Point** & **1** & **2** & **3** & **4** & **5** & **6** & **7** \\ \hline Expert subjective evaluation method & I & I & I & II & III & IV \\ Combined objective weighting–SPA & I & I & I & II & III & III & II \\ Combination weighting–SPA & I & I & I & II & II & III & III \\ \hline \hline \end{tabular}
\end{table}
Table 7: Comparison of Evaluation Results.  
(2) The five evaluation indices were selected by the combination weighting-SPA model for the selection of lining forms of diversion tunnels, according to the three design criteria commonly used in hydraulic tunnels. Therefore, this model has certain representativeness and applicability. For the high-pressure pipelines to be evaluated, a similar suitability rating model for lining forms can be established by selecting evaluation indices with similar property characteristics. However, for different hydraulic tunnels, there may be different geological characteristics and risk environments. Therefore, the evaluation indices can be increased or decreased appropriately to meet the suitability evaluation of reinforced concrete lining forms for different high-pressure pipelines.  
(3) There are still shortcomings in this study. The hydraulic tunnel design criterion in the proposed model is relatively conservative and basic. For complex cases, how to integrate weights into the evaluation model for the selection of lining forms and how to consider the effects of the index on lining stability remain to be clarified, and further efforts need to be made on accurately selecting an appropriate lining form to prevent accidents in the future. Therefore, a more scientific, rational, and universal classification standard needs to be realized through further research.