为揭示青藏高原高海拔长大隧道凝灰岩地层大变形特征及其影响因素，以川藏公路矮拉山隧道为依托，采用现场调研、监控量测数据分析和数值模拟方法分析大变形段地应力分布特征、变形及破坏特征，讨论高海拔长大隧道大变形影响因素。研究表明： 1）矮拉山隧道大变形段以水平构造应力场为主，其量值是自重应力场的2.12~2.8倍； 2）初期支护变形破坏特征主要表现为初期支护开裂、掉块、钢架扭曲、侵限； 3）470 m二次衬砌左右边墙存在55条长度、宽度、深度及走向各异的裂缝； 4）仰拱以中部隆起为主，最大隆起达382 mm，隆起不均匀并有弯曲破坏发生； 5）拱顶沉降量为268.80 mm，最大水平收敛值为924.9 mm，最大变形速率为110.27 mm/d，具有变形量大、变形速率快、持续时间长、变形发生部位集中的特点； 6）初始高地应力场环境和软弱凝灰岩岩性条件是矮拉山公路隧道发生大变形的主要影响因素，原设计二台阶法施工工法和支护时机以及支护结构刚度不足等是发生大变形的重要影响因素。

To investigate the characteristics and influencing factors of the large deformation in the tuff stratum of the long and highaltitude tunnels located in the QinghaiTibet Plateau, the field investigation, monitoring data analysis, and numerical simulation are adopted to analyze the characteristics of stress distribution, deformation, and failure of large deformation section and discuss the influencing factors for large deformation in highaltitude area. The research and analytical results show the following: (1) The horizontal tectonic stress field is the main stress field in the large deformation section of Ailashan tunnel, and its magnitude is 2.12~2.8 times that of gravity stress field. (2) The deformation failure characteristics of the primary support are mainly manifested as cracking, falling blocks, steel frame distortion, and boundary intrusion. (3) There are 55 cracks with different lengths, widths, depths, and directions on the left and right sidewalls of the secondary lining. (4) The inverted arch is dominated by the central uplift, with a maximum uplift of 382 mm, while the uplift is uneven and the bending failure occurs. (5) The settlement of the crown is 268.80 mm, the maximum horizontal convergence is 924.9 mm, and the maximum daily deformation rate is 110.27 mm. The large deformation is characterized by large amount, fast rate, long duration, and concentrated location. (6) The initial high ground stress field and the lithologic conditions of soft tuff are the main influencing factors for the large deformation of the Ailashan highway tunnel, and the construction method of the original twobench method, the supporting time, and the insufficient stiffness of the supporting structure are the important influencing factors for the large deformation.