新建兰渝铁路木寨岭隧道为双洞单线分离式特长隧道，全长19 km，施工过程中在高地应力和软弱围岩的共同作用下出现了难以控制的大变形问题，对施工安全和顺利进展都造成较大影响。为解决这一问题，通过现场试验的方式，采用超前大钻孔对地层高地应力进行预释放，以减小作用于支护结构上的压力，使支护系统受力处于安全范围内，达到控制变形的目的。对大钻孔施工及施工效果进行分析，试验表明超前钻孔对后期的变形发展有所遏制，但对隧道施工也会产生一定影响，其现场的应力释放效果及施工组织等方面还需进一步研究和完善。

Muzhailing tunnel on LanzhouChongqing railway is a 19 kmlong twintube tunnel. Due to the high ground stress and the soft rock, large deformation occurs during the construction of the tunnel, which has great influence on the safety and successful construction of the tunnel. By drilling largediameter boreholes in advance to release the stress, the stress on the support structure is reduced, the deformation is brought under control and the support system becomes safe. In the paper, the construction and the effect of the largediameter boreholes are analyzed. Conclusions drawn are as follows: The largediameter boreholes drilled in advance can restrict the development of the deformation，but has some negative influence on the tunnel construction; The stress releasing effect and the construction organization of the largediameter boreholes should be further studied and improved.