Prediction of risk event path for shield tunneling of long-distance water conveyance tunnel
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Abstract:
In order to solve the problems of uneven distribution of water resources, mismatched water and soil resources, and serious shortage of water resources, China has launched many long-distance water diversion projects during recent years. With the implementation of these projects, a large number of headrace tunnels has also been constructed, which is continuously developing and improving the construction methods, and now the shield method has gradually become the main construction method of tunnels. As the shield tunneling is a complex system process influenced by a variety of risk factors, construction risk accidents occur from time to time, resulting in delays of the construction period as well as loss of life and property. Therefore, predicting and analyzing the possible risk path of the shield tunneling of long-distance water conveyance tunnel plays an important role in ensuring the safe construction of the tunnel project.At present, the risk analysis of tunnel shield construction schedule have several limitations. First, the correlation between the risk factors of shield tunneling of headrace tunnel is not considered; Secondly, the existing research results are mostly based on subway and traffic tunnel, and the differences in construction technology and risk management of long-distance headrace tunnel of hydraulic engineering are not considered. This paper takes the shield tunneling of long-distance water conveyance tunnel in the water diversion project of hydraulic engineering as the research object. Statistical analysis are made on a large number of collected data of water diversion tunnel construction cases, and the risk causing indicators and possible risk events are extracted of tunnel engineering shield tunneling. By using interpretative structural model, the causal hierarchy analysis and network topology diagram construction are conducted. Then a prediction model of shield construction risk events based on Bayesian network is established, and the reliability of the model is preliminarily verified through Bayesian network learning.Finally, the risk event prediction model obtained has been applied to the shield construction project of Xixiayuan Chuanqin Tunnel. The reverse diagnosis reasoning technology of Bayesian network is used to calculate the maximum possible path of risk events and determine the key factors leading to risk events in shield construction. The results show that the risk accident path calculated by the model is consistent with the actual construction situation at the current stage of the project. The reliability and applicability of the model are verified, and according to the prediction results of the risk accident path, the guidance is provided for the troubleshooting and governance of the risk hidden dangers in the subsequent construction of Chuanqin Tunnel.Conclusion: (1) The risk path prediction model of tunnel shield construction is established. Through the interpretation of the structural model, the correlation between various risk events that affect the tunnel shield construction progress is determined, and then the Bayesian network model is established, forming an effective method to predict the development trend of the tunnel shield construction risk events through the tunnel shield construction risk factors. (2) The reliability and applicability of the model are verified. Through the application of the shield construction project of Chuanqin Tunnel Project, the predicted result of risk causal chain is consistent with the actual construction situation, and the model can provide real-time decision support for managers. (3) This model can be directly applied to shield tunneling of headrace tunnels with similar construction conditions; for different situations, such as special geological conditions and different shield machines, some parameters of the model need to be appropriately changed, but the model and calculation process established in this paper are applicable.
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