1.上海市科学技术委员会“青年科技英才扬帆计划”项目（编号：15YF1412800） 2. “中央高校基本科研业务费专项资金”项目（编号：2014KJ016 和 10247201571）
Subgrade fillers in the vicinity of bridge abutments are very difficult to be well compact. And the material of subgrade fillers is inhomogeneous. As a result the variability of subgrade stiffness is observed. Focusing on the effect of the key uncertainties on the dynamic properties and the safety evaluation of the dynamic design of the transition zone, and based on the theory of the railway system dynamics, a plane strain finite-infinite element model is employed to investigate the system dynamics of a subgrade-bridge transition zone. In this model, the vertical force coupling for the rail and the substructure is achieved by modifying the fastening spring stiffness matrix and the infinite element method is employed to prevent the wave reflection on boundaries. With this model and the stochastic finite element method based on the Latin hypercube sampling method, The influence of the parameter variability of subgrade stiffness on dynamic response of vehicle-track coupling system in the transition zone is investigated. The results indicate that the influence of the variability of subgrade stiffness on the rail vertical dynamic displacement is greater than that of the wheel-rail contact force and the acceleration of the vehicle body. The dynamic response of transition zone is more sensitive to the parameter variability of the filler in the transition zone than that of the subgrade surface layer. Dynamic response data deviate from normality, and at the 95% confidence level, the maximum value of the acceleration of the vehicle body and the wheel-rail force approximately obey the Weibull distribution. While the data distribution of the maximum value of the rail vertical dynamic displacement presents obvious “high peak and thick tail”, and it is easy to appear the abnormal large value. In order to reduce the vertical dynamic displacement of the rail and facilitate the construction quality control, the subgrade stiffness of the transition section should be improved. The maximum value of the rail vertical dynamic displacement is selected as the safety evaluation index of the dynamic design of the transition zone and the result reveals that the fuzzy failure probability of the current design is 0.00045 and the design is safe.