Research on Railway Tunnel Duration Risk Assessment Based on the Improved PERT Model

Based on the railway tunnel construction network planning with the characteristics of Precedence Network (PN) and Parallel Path (PP), taking into account the classical PERT (Program Evaluation and Review Technology)model can only be used for general network planning risk assessment analysis. Introducing three conceptions into this article, named Virtual Time Procedure X_jk, Correlation Path, Leading Path Respectively. Then, PN can be transformed into the general PERT of virtual time procedure X_jk. On this basis, and further puts forward a modified general PERT method that use of the Influence of Leading Path on Correlation path to solve the problem of the PP. Based on the method, the improved PERT model used to railway tunnel duration risk assessment were put forward, and the proposed model was applied to one tunnel (43.8 kilometers long two-lane ) in Fujian Province, two kinds of analysis cases were drafted, and make the result more acceptable to the Accurate MC method. The results show that The improved PERT model are of clear physical meaning, and which can solve the complex network of PN and PP; if there are no plans to consider the PP and PN, the calculated value of the expectations of small period, large variance; By accurate MC methods and the use of this paper to propose the analysis of PERT model, the result is closer to, and thus the improved PERT model has good accuracy.