Ma'anziliang long highway tunnel is typical separated tunnel of Shiyan-tianshui expressway which is located in complicated geological conditions in Qinba mountain area. Reliability of initial support of grade V surrounding rock section was analyzed by using finite element method. The supporting structure of the highway tunnel is important to traffic safety. Ma'anziliang highway tunnel is a typical long tunnel under complicated geological conditions. According to lithology of grade V surrounding rock and primary support parameters, the structure factor of safety was calculated about bolt resistant tension, bolt length and shotcrete force through finite element method. As a result the reliability is evaluated and the coefficient is 0.588, but integral structure will be steady if taking secondary lining into account.

During the process of tunnel construction and using, the safety of primary support need to be analyzed and evaluated. At present, the analysis methods of primary support reliability in highway tunnel were probabilistic methods and finite element method. For example, the finite element simulation method was usually used in calculation of slope safety factor, which could analyze the stability of slope (Chen & Liu 2010, Liu et al. 2009, Zheng et al. 2005). In recent years, the evaluating method using safety factor of surrounding rock stability and support structure was used in underground works (Han & Su 2011, 2012, Han 2012). Depended on Ma'anzi Liang tunnel in QinBa mountain, this paper mainly was acquired the safety factor of primary ·support in surrounding rock V. At the same time, the reliability of support structure was evaluated.

1.1 Tunnel introduction

Ma'anzi Liang tunnel is a typical separate type and longer tunnel in ShiTian xian highway. Right line start at YK34+614~YK39+539 and the total length is 4925 m. The pile number of V-class surrounding rock were (YK34+625~YK34+728 (103 m), YK38+467~YK38+693 (226m) and YK39+372~YK39+533) (161 m). The New Austrian Method was used in this tunnel, and bench method was used in excavating in the area of V-class surrounding rock. Among them, reserved core soil was taken annulary in excavating in upper bench and lower bench partially staggered around the excavation.

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