由于单拱4车道公路隧道通常采用扁平的拱形结构形式，从而导致隧道开挖后围岩的二次应力分布不均匀，初期支护的支护效果不佳。为了研究采用不同施工方法时各种初期支护手段的力学特征，采用有限差分软件FLAC3D对不同围岩条件下单拱4车道公路隧道的施工动态过程进行了三维数值模拟，得到了不同施工方法下初期支护的应力和位移特征。通过比较分析这些力学特征，提出了不同围岩条件下使初期支护达到最佳效果的施工方法。

Due to the flat arched structure usually adopted in singlearch fourlane highway tunnels, the distribution of the

secondary stresses in the surrounding rock mass after tunnel excavation is nonuniform and the reinforcement effect of the primary

reinforcement elements is poor. In order to study the mechanical characteristics of the primary reinforcement elements under

different construction methods, the dynamic construction processes of singlearch fourlane highway tunnels in different

surrounding rock mass are simulated by finite difference software FLAC3D and the stress and displacement characteristics of the

primary reinforcement elements under different construction methods are obtained. By comparing these mechanical characteristics,

construction methods under which the optimum reinforcement effect of the primary reinforcement elements can be reached are proposed.