长大隧道施工中通常采用设置辅助坑道增加作业面提高项目施工进度，然而辅助坑道进入正洞的挑顶施工通常是长大隧道施工的难点，三岔口的设置对隧道施工的影响较大。本文结合成兰铁路平安隧道横洞进正洞时设计的3种不同全断面挑顶施工方案，并通过应用总结了不同挑顶施工方案的特点，确保隧道在安全、质量的前提下达到快速进洞的施工条件。增加支洞施工方案和横洞断面不同比扩大垂直进正洞挑顶设计明显优于横洞断面同比例扩大垂直进正洞挑顶设计。

Auxiliary galleries are always adopted in long tunnel construction so as to shorten the construction period. The construction of the connection section between auxiliary gallery and main tunnel is difficult and the arrangement of it affects the tunnel construction obviously. The characteristics of 3 different construction schemes of connection section between horizontal gallery and main tunnel of Ping’an Tunnel on ChengduLanzhou Railway are summarized. The results show that the schemes of adding branch tunnel and enlarging construction of horizontal gallery step by step is superior to the scheme of direct enlarging construction of horizontal gallery.