Reliability Of Single-Track Railway Tunnel Lining Under Geologically Asymmetric Pressure

Combining with the engineering characteristics of the geologically asymmetric pressure in the left line exit of Maoxian railway tunnel, the finite element software ABAQUS was applied to deal with the weak surface living in geologically asymmetric pressure rock, and to select the appropriate contact element and the friction type, and then calculate the two-dimensional model of single-track railway tunnel under geologically asymmetric pressure. Basing on the previous results, the reliability of secondary lining structure was further analyzed, and the reliability in asymmetric lining structure was discussed carefully according to the last analysis about the reliability in symmetric lining. The main contents of this thesis has the following aspects:(1) Refining Effective physical and mechanical parameters of the surrounding rock and lining utilizing in engineering background, this thesis combined with relevant specifications and documentation to handle the shape and characteristic parameters of the weak structure surface and finally established a two-dimensional tunnel model with features of geologically asymmetric pressure.(2) According to the analysis and calculations of the two-dimensional model of the tunnel under geologically asymmetric pressure, the internal force and stress and displacement of the surrounding rock and the lining had been gotten. Random input and output variables used in the reliability of secondary lining structure were determined according to the conclusions and the model established.(3) Applying single-factor control variable method to calculate conditions of the tunnel model after determining the basic random input and output variables in reliability analysis, this thesis drew the conclusion of the output variables on the single factor expression. Repeat the above works and obtain the single-changed functions of all random input variables, and then use multiple regression analysis to get the explicit expressions of output variables with the input variables. The FOSM and JC reliability analysis methods had been used to analyze and summarize the reliability of lining structure in this tunnel model. From the results, the simulated model of the tunnel lining was reliable, and the reliability of the left spandrel and the waist was smaller than the right side at the corresponding symmetrical parts. The parts with small reliability were weak in the overall structure, and were necessary to take appropriate measures to strengthen.(4) On the basis of the reliability analysis conclusion of the tunnel, an asymmetric form lining structure was proposed to improve the stress state of the tunnel under geologically asymmetric pressure for the purpose of reducing correspondingly disadvantageous effections. The improved reliability form was analyzed and checked whether the form had some engineering significance so that we could put forward effective project proposals and measures.So the final conclusions showed that this form in the tunnel was possible to increase the lining reliability of the weak position, and beneficial to the overall stability of the asymmetric lining structure.