由于山子顶软弱围岩公路隧道施工现场所采用的环形开挖留核心土法并不能保证隧道施工的顺利进行，提出扩挖支护施工方案。首先论述扩挖支护施工工序，然后采用ANSYS有限元方法构建扩挖支护厚度为0、20、30、40、50、60 cm 6种三维计算模型，系统分析扩挖支护与初期支护的力学行为。研究得出： 扩挖支护是软弱围岩隧道一种相对优越的施工方案，且当扩挖支护厚度达到60 cm时初期支护的主压应力为16.4 MPa，主拉应力为0.486 03 MPa，满足其材料强度要求。

The annular excavation with core soil method used in Shanziding Highway Tunnel can not guarantee successful tunnel construction in weak surrounding rock, so the expanding lining method is put forward. First, construction sequences of expanding lining method are discussed; and then, ANSYS finite element method is adopted to establish 3D computational models for expanding lining with thicknesses of 0, 20, 30, 40, 50 cm and 60cm; finally, mechanical behaviors of expanding lining and primary support are analyzed. It is concluded that expanding lining is a relatively superior method for tunnel construction in weak surrounding rock; and when thickness of expanding lining reaches 60 cm, principal compressive stress and tensile stress of primary support are 16.4 MPa and 0.486 03 MPa respectively, which can meet the material request.