Abstract:The load-bearing model for middle wall is established. The criterion for stability of middle wall in multi-arch tunnel and tunnel with small spacing is presented through theoretical analysis. According to the criterion,the rational thickness of the middle wall can be obtained. Taking Baziling forked tunnel for example,the whole construction process of the tunnel is simulated by geomechanical model test and elastoplastic damage finite element program respectively. The change curves of displacement and stress at key points with construction steps and the distribution of damage zone and plastic zone in surrounding rock are presented;and the optimization measures for construction process are put forward. The influence of blasting construction on tunnel stability is also researched;and the quantities of charge and construction measures under the conditions of different middle wall widths and different surrounding rocks are presented. According to the research results,the suggestions are made to modify the original construction design. The field monitoring for construction is conducted for forked tunnel. The comparison among the monitoring,testing and calculating data validates the model and numerical result. The monitoring results show that the tunnel is stable,which proves that the suggestions for construction optimization are reasonable.