In this paper, a large section tunnel of Beijing metro line 4 is regarded as research background, Two kind of different supporting calculation models( The first supporting calculation model is that the total load is applied to the initial support and inner support, and the second supporting calculation model is that the action effect of initial support can be ignored and the total load is applied to the inner support)are cmployed respectively to calculate the safety factor and reliability index for tunnel structure. The calculation result indicate that the tunnel structure safety factor meet the safety challenge. However, the tunnel reliability index cannot meet the safety challenge requirement with the second calculation model. Based on the result of the tunnel structure loading effect with the response surface method, the equivalent stratum elastic resistant coefficient is put forward to describe the role of initial support. The result provides a treating path to solve the reliability index difference by using different support model.%以北京地铁四号线某大断面矿山法隧道为背景,分别应用"初期支护与二次衬砌共同承受全部荷载的计算模式"与"不考虑初期支护承载而由二次衬砌单独承受全部荷载的计算模式"进行隧道截面安全系数和可靠度指标的计算,结果表明:两种承载模式得到的结构最不利截面安全系数均能满足要求,但"二衬结构单独承载模式"得到的最不利截面结构可靠度指标偏低.为确保根据不同承载模式得到的计算结果基本相同,在应用响应面法分析隧道衬砌结构荷载效应的基础上,采用了等效地层弹性抗力系数来表征初期支护对结构承载的贡献,为解决地铁隧道结构设计中由于结构承载模式不同而造成的计算结果差异提供了一个途径.
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