## 4 Discussion
The two-dimensional scatter plot of traditional evidence conflict and improved model evidence conflict is shown in Figure 7. The following conclusions can be obtained:  
1. Figure 6 is the confusion matrix diagram of different models. The ordinate represents the test results, the abscissa represents the real results and the numbers in the diagram represent the number of tunnel sections. In Figure 6a, the total number of tunnel sections is 60, which is the sum of all tunnel sections in the figure. In the figure, the number 8 indicates that the number of tunnel sections with 'risk prediction grade I and actual grade I' is 8. Similarly, the number 4 indicates that the number of tunnel sections with 'risk prediction grade II but actual grade I' is 4. Therefore, the number of tunnel sections with the same prediction level and the actual level can be obtained by adding the numbers of the diagonals in the figure, that is, the number of tunnel sections predicted by the model is correct. The ratio of the number of tunnel sections to the total number of tunnel sections can obtain the prediction accuracy of the model. The accuracy of Advanced Geological Prediction (Figure 6a) is 62% ((\(8+17\)\(+\)\(9+3\))/(\(8+4+3+1+3+17+3+2+2+2+9+2+0+0+1+3\))). Similarly, the accuracy of Field Inspection (Figure 6b) is 56%, the accuracy of Instrument Monitoring (Figure 6c) is 68%, the accuracy of Traditional D-S (Figure 6d) is 73% and the accuracy of Improved D-S (Figure 6e) is 88%. 2. The accuracy of the single-source information evaluation method (Figure 6a-c) is less than 70%, which cannot provide accurate decision-making suggestions for construction. The single information source method does not fully consider the risk factors of collapse, making the assessment slightly biased. The accuracy of the traditional D-S evidence fusion method is 73% (Figure 6d), which is slightly higher than that of the single-source information evaluation method, but the accuracy is still low, and it cannot provide accurate guidance for the construction site. As shown in Figure 6e, the multi-source information fusion method has a high evaluation accuracy (88%). This is because the multi-source information model comprehensively considers the advanced geological forecast, on-site inspection and monitoring data, making the evaluation model closer to the actual situation. At the same time, the proposed method considers the importance and credibility, ameliorating the high conflict evidence, making full use of the available information, and improving the accuracy of the evaluation results. 3. The traditional D-S method and the proposed method are used to evaluate the risk of section YK223 + 473 respectively. Taking the conflict threshold as the reference value, the traditional D-S method (Figure 7a) has some evidence conflict values higher than the threshold and are more discrete. After the proposed method (Figure 7b) is identified and adjusted, the excess evidence conflict has been greatly improved, which is basically below the threshold. In addition, the adjusted evidence conflict values are relatively concentrated and less discrete. The analysis results further show that the proposed method not only has higher recognition accuracy, but also can effectively improve the high evidence conflict.