超短台阶法在黄土隧道施工中的适用性分析

Applicability of ultrashort step method in loess tunnel construction

以在建的国道309线固原过境段公路九龙山隧道为工程背景,对V级围岩采用长台阶法、短台阶法、超短台阶法三种方案比选。以洞内变形、初支喷层的最大主应力和最小主应力、施工难点作为控制条件,利用数值模拟进行分析。结果表明:采用超短台阶法可以明显减小支护结构中的主拉应力,避免初支喷层发生拉裂破坏,并且能够有效解决上下断面相距较近、机械设备较集中的问题。最终给出对本段隧道开挖方式的施工建议,并据此指导施工,实现本段隧道的顺利贯穿。

Jiulongshan highway tunnel on Guyuan transit section of 309 National Road under construction is taken as the engineering background of the thesis. The scheme comparison of long step method,short step method and ultrashort step method are conducted for the V grade wall rock. The cave deformation,the maximum principal stress and minimum principal stress of the initial support sprayed layer,and construction difficulties are taken as control conditions. The results of numerical simulation analysis show that the use of ultrashort step method can significantly reduce the main tensile stress of the supporting structure,thus avoiding tensile failure of the initial support sprayed layer. Finally,construction recommendations are given for the excavation of the section of the tunnel,which is used to guide the construction in order to achieve a smooth throughout of this section of the tunnel.