为防止隧道围岩失稳，探明膨胀黄土遇水局部膨胀对隧道支护结构安全性的影响规律，以某黄土隧道为依托，采用温度应力场模拟膨胀黄土增湿产生的湿度应力场，运用FLAC 3D软件热-力耦合模块研究膨胀性黄土局部（隧道拱部、拱腰、边墙、仰拱）遇水发生膨胀作用对隧道支护安全性的影响。研究表明： 1）处于局部膨胀区域的结构变形明显，仰拱隆起变形除受自身所处膨胀区域影响明显外，受其他部位膨胀作用也较为明显，是变形主要位置；在局部膨胀作用下，拱顶部位沉降变形最为显著，而拱腰和墙中部位变形次之，墙脚变形最弱。2）处在浸水膨胀区域的支护最大主应力随着膨胀力增加而增加，且大部分表现为线性增加；膨胀力为200~300 kPa时，膨胀区域支护结构拉应力超过C25混凝土轴心抗拉强度标准值1.27 MPa； 3）局域膨胀区域内围岩破坏以受拉破坏为主，仰拱下方围岩在自身膨胀作用下以及其他部位局部膨胀作用下皆表现出受拉破坏，是应力集中部位； 4）采用结构安全系数法，确定结构不同部位承受最大膨胀压力以及变形值，拱顶、拱腰、边墙、仰拱能承受的最大局部膨胀压力分别为223、260、292、238 kPa，对应的破坏变形为87、36、47、27 mm。

The influence law of local expansion of expansive loess on the safety of tunnel support is key to keeping surrounding rock stable. Based on a loess tunnel, the temperature stress field is built to simulate the humidity stress field generated by the humidification of expansive loess, and thermalmechanical coupling module of FLAC 3D software is used to study the influence of expansive loess on the safety of support under the condition of local expansion (tunnel arch, arch waist, side wall, and inverted arch) when encountering water. The results show that: (1) Structure deformation in local expansion area is obvious; inverted arch deforms obviously not only when it is located in local expansion area, but also when affected by the expansion of other parts, thus it is the main deformation position; under the effect of local expansion, the deformation of arch crown is the largest, the deformation of the arch waist and the side wall is the second, and the wall foundation is the weakest. (2)The maximum principal stress of support in waterimmersed expansive area increases with the expansive force, and most of them increase linearly; when the expansive force is between 200 kPa and 300 kPa, the tensile stress of support structure in expansive area exceeds the standard value of C25 concrete axis tensile strength（1.27 MPa）. (3)The failure of surrounding rock in local expansion area is mainly tensile failure; the surrounding rock under inverted arch shows tensile failure under its own expansion and local expansion of other parts, which is the stress concentration part. (4) By using the method of structural safety factor, the maximum expansion pressure and deformation value of different parts of the structure are determined; the maximum local expansion pressure of the tunnel arch, arch waist, side wall， and invert arch are 223 kPa, 260 kPa, 292 kPa， and 238 kPa respectively, and the corresponding deformation is 87 mm, 36 mm, 47 mm， and 27 mm respectively.