Taking Humaling tunnel as the engineering background, site monitoring together with 3D numerical simulations were adopted to analyze the variations of the stress field, displacement field and plastic field of the surrounding rock in loess after tunnel excavation. Meanwhile the factors affecting the mechanical response of surrounding rock were studied during the bench method construction. Results show that the contact pressure of the surrounding rock is rather unevenly distributed. The haunch, wall corner and side wall are the weak links in the construction process. Measures should be taken, such as strengthening the support stiffness, setting the locking bolt or expanding arch foot. It is suggested to ignore the systematic bolt, which is not only helpful to the deformation control of surrounding rock but also can reduce project investment. The supporting structure has reasonably adjusted the stress distribution of surrounding rock, improved the stress concentration and controlled the expansion of the plastic zone. Hence, the principle of "timely support and early ring closure" should be insisted on. The support of the upper bench plays an important role in the control of crown settlement, to which more attention should be paid in the construction. The crown settlement is within the allowable range of deformation, which indicates that the current designed support parameters meet safety requirements. The influence range of tunnel face spatial effect is approximately 2~3 times of the tunnel diameter ahead. The result of numerical calculation basically tallies with that of the site measurement.%以胡麻岭隧道为工程背景,采用现场监测与三维数值模拟结合的方法,分析隧道开挖后黄土围岩应力场、位移场与塑性区的变化规律；同时对台阶法施工中影响围岩力学响应的因素进行分析.结果表明:围岩接触压力分布很不均匀；拱腰、墙角和边墙是施工过程中的薄弱环节,应加强支护刚度,设置锁脚锚杆或扩大拱脚；建议取消拱部系统锚杆,既有利于控制围岩变形又可减少工程投资；支护结构调整了围岩应力的分配,改善了应力集中且控制了塑性区的发展,故应坚持“及时支护、及早封闭成环”的原则；上台阶支护对控制拱顶沉降起着关键作用,施工中应引起足够重视；拱顶沉降在变形允许范围内,说明现行支护设计参数满足安全性要求；掌子面空间效应的影响范围约为其前方2～3倍洞径；数值计算结果与现场实测结果基本吻合.
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