中文摘要：

以某高速公路大跨径隧道为例,应用有限元软件MIDAS/Gen模拟两种围岩条件下采用台阶法施工的隧道开挖支护情况.模拟结果表明对处于Ⅲ级与Ⅳ级之间的隧道围岩,当为片理化非均质岩体,且上台阶围岩质量比下台阶好时,水平和竖向位移较大区域均集中于隧道底部,且变形超过了规范允许值,宜采用Ⅳ（A）级围岩支护设计进行施工,但钢拱架间距可放稀至100 cm;当非均质岩体上下台阶围岩质量均较好时,其最大水平位移较小,竖向位移最大值发生在拱顶,且在相关规范允许范围内,可按Ⅳ（A）级围岩进行支护,但可取消仰拱,实现对支护设计的优化.

英文摘要：

Taking the large span tunnel of freeway for an example,this article makes numerical simulation about tunneling supporting with bench method in two different conditions of surrounding rocks.The simulation results show that when surrounding of tunnel is cleaved and inhomogeneous rock mass between level Ⅲ and Ⅳ and surrounding rock of up bench is better than down,there is much horizontal and vertical displacement in the bottom of tunnel.In addition,it should be used with supporting method for Ⅳ （A） class surrounding rock beside the steel arch spacing can be put diluted to 100 cm.One the other hand when each bench of inhomogeneous rock mass is better than before,there is less maximum horizontal displacement and the maximum vertical displacement occurred in the vault.However we can cancel the construction of inverted arch with supporting method for Ⅳ （A） class surrounding rock in the range of allowable related specifications,thus providing more optimization for supporting design.