针对蒙华铁路段家坪隧道岩爆段初期支护在较小变形下发生破坏现象，通过室内试验、超前地质预报、地应力测试等技术手段，分别揭示洞周围岩强度、掌子面前方地质情况和初始地应力状态，同时对初期支护变形破坏特征进行归纳总结并分析成因，得出： 围岩特性、地质构造特征、工法是影响初期支护变形破坏的重要因素，局部水平向高地应力是主因。采取增强支护参数、增设缓冲层、锚杆+加筋底板、加装阻尼器等技术措施控制初期支护变形破坏。研究结果表明： 1）以水平构造应力为主的高初始地应力条件下，若隧道洞身围岩竖向节理发育，开挖宜首选二台阶法。2）拱部及仰拱初期支护混凝土破坏类型为剪压破坏,格栅钢架主筋破坏类型为偏心受压屈曲。3）以水平构造应力为主的高初始地应力状态下，宜根据围岩特性、支护原理及现场实际选择相应的技术措施。

In view of the failure phenomenon of the primary support with small deformation in the rockburst section of Duanjiaping Tunnel on Menghua Railway, the rock strength around the tunnel, the geological conditions ahead of tunnel face and the initial geostress state are revealed by laboratory test, advance geological prediction, geostress test and other technical means; and the deformation and failure characteristics of the primary support are summarized and the causes are analyzed. It is concluded that the characteristics of surrounding rock, geological structure and construction method are the important factors affecting the deformation and failure of the primary support, and the local horizontal high geostress is the main cause. The deformation and failure of the primary support can be effectively controlled by technical measures, including strengthening the support parameters, adding buffer layer, adopting bolt and reinforced floor, adding damper, etc. The results show that: (1) The twobench method should be selected preferentially for excavation when the vertical joints are developed in surrounding rock of tunnel body under high initial geostress condition, which is dominated by horizontal tectonic stress. (2) The failure mode of the primary support concrete of arch and inverted arch is shear compression failure， and the main reinforcement failure mode of grid steel frame is eccentric buckling. (3) According to the characteristics of surrounding rock, supporting principle and field practice, corresponding technical measures should be adopted in case of high initial geostress, which is mainly composed of horizontal tectonic stress.