Limit State Design Method of Railway Tunnel Portal Based on Reliability Theory

From the characteristics that limit state functions for the stability of a railway tunnel portal structure are nonlinear and the parameters are random, a new design method for railway tunnel portal structures was put forward based on the reliability theory. Limit state equations for railway tunnel portal structures were founded by analyzing the limit states of railway tunnel portal. Based on the reliability theory, reliability indices of a single-track railway tunnel portal with a design speed of 140 km/h were calculated as an example, target reliability indices for different limit states were determined from the calculated reliability indices of railway tunnel portal under three design speeds, including 16 kinds of portal forms and 22 kinds of portal categories, and partial resistance coefficients were calculated and optimized based on establishing the design expressions for different limit states. The research results show that major limit states of railway tunnel portal are cracking, crushing, overturning stability, sliding stability and insufficient foundation bearing capacity; the statistical characteristics of basic random variables in the limit state equations are the key whether reliability design of railway tunnel portal is accurate or not, and the determination of the reliability indices is the core issue in the limit state design of railway tunnel portal. The established method can be directly used to the limit state design of railway tunnel portal.