研究结果：大断面隧道进洞施工时，洞口地形复杂、地质条件较差、结构受力状态复杂，需要采用不同于隧道正洞的施工辅助措施。本文给出了大管棚法、接长明洞法、小导洞进洞反向施工法、地层反压法等几种常用的隧道进洞施工方法，并结合工程实例对大断面隧道削竹式洞门进洞施工进行了分析。

Research results: It is necessary to take the different construction auxiliary measures from those for construction of tunnel main portal because of complicated landform of tunnel face, bad geological conditions and complicated stressed status of structure when the start tunneling is conducted for the tunnel with big cross section and cutting face. Some commonly used methods for start tunneling are presented, such as big pipe shed method, spreading cut and cover tunneling method, little pilot hole reverse construction method and counter pressure on strata method, and the analyses of start tunneling of the tunnel with big cross section and cutting face are made in combination with the construction practice in this paper.