# Dynamic Risk Assessment of Ultra-Shallow-Buried and Large-Span Double-Arch Tunnel Construction
## 7 Conclusions  
The main problem that faced this study was to overcome the deficiency of static risk assessment in an ultra-shallow-buried large-span double-arch tunnel. Xiamen Haicang double-arch tunnel was selected as an example, and the dynamic risk assessment was investigated for the ultra-shallow-buried large-span double-arch tunnel construction. Firstly, the construction process was divided into five stages, and the dynamic risk evaluation index system was established. Then the benchmark weight of the dynamic risk evaluation index was determined by AHP, and the weight of risk evaluation index was modified according to the construction stage. The risk evaluation indexes of the different construction stages were determined differently, and the weights of the risk evaluation indexes at the same level were changed during the construction process. The changes in weights affected the risk assessment results. Finally, the fuzzy comprehensive evaluation method was adopted to evaluate the risk of each stage, and the risk control measures were suggested. Therefore, the following conclusions can be drawn:  
(1) Dividing the construction into different stages for risk evaluation according to the construction process and the key construction nodes improved the accuracy, timeliness, and rationality of the dynamic evaluation results;  
(2) The risk assessment result of the main tunnel double tunnel excavation stage was level II, and the risk level was high. The risk assessment result of the ground and surrounding rock reinforcement stage was level IV, and the risk in this stage was low. The risk assessment results of the other stages were level III, and the risk was medium;(3) In the pre-construction preparation stage, comprehensive risk prevention policies and risk treatment measures should be formulated, and the monitoring of the items required by the specification during the project must be strengthened. No risk treatment measures were needed at the surface and surrounding rock reinforcement stage. During the construction of pilot tunnel and single tunnel excavation stages of the main tunnel, attention should be given to the changes in monitoring data. Great attention must be given to the risk in the excavation stage of the double tunnels of the main tunnel;  
(4) The dynamic construction safety risk assessment based on the fuzzy comprehensive assessment method is more timely, accurate, and reasonable than the traditional assessment method. Dynamic risk assessment can promptly discover and prevent hidden dangers in the construction of shallow-buried tunnels. Summarizing the research performed above, it can be concluded that the dynamic risk assessment of the Xiamen Haicang tunnel objectively reflected the dynamic risks. However, the dynamic risk identification of an ultra-shallow-buried and large-span double-arch tunnel construction maybe complex and uncertain. The influencing factors are normally determined by the experience of experts. The dynamic assessment currently depends on quantitative work. In the future, random field theory and probability method can be introduced to describe the risks, quantitative methods including artificial intelligence (AI), big data, digital technology, and AI monitoring can be involved in the dynamic assessment to identify the number of risk factors and improve the accuracy of risk assessment. [PERSON], [PERSON] and [PERSON] carried out the main research task and wrote the manuscript. [PERSON] proposed the original idea and contributed to the revision of the obtained results and of the whole manuscript. [PERSON], [PERSON] ([PERSON]), [PERSON] performed utilization on-site. [PERSON], [PERSON] ([PERSON]), [PERSON], [PERSON] and [PERSON] performed the investigation. All authors have read and agreed to the published version of the manuscript.