Serious cracks of secondary lining appear at the entrance section of a highway tunnel in southwest China after excavation. The entrance section of the tunnel has geological characteristics of bedded rock mass with inclined structural plane, asymmetrically loaded terrain, shallow buried depth, and soft surrounding rock. This paper aims to explore the cracking mechanism of lining at the entrance section and propose reinforcement measures to prevent the structural damage accordingly. Site investigation was conducted to demonstrate the cracking characteristics (process, distribution, width, and depth) of tunnel lining. Cracks mainly appeared on the interior lining of left arch-haunch and right side-wall, as well as on the exterior lining of right arch-haunch. The deformation of secondary lining in cracking section was monitored and analyzed to explore the deformation characteristics after the appearance of cracking and installation of temporary supporting. Then, a three-dimensional finite difference numerical model based on the actual terrain was built to analyze the spatial mechanical characteristics of the entrance section. A deformation analysis model including four zones of the surrounding rock was used to analyze the cracking mechanism of asymmetrically-loaded tunnel with inclined weak structural plane. Finally, ground reinforcement measures and reversed loading to control deformation of bedded rock mass and tunnel structures are proposed. Investigating the cracking case of the tunnel has significance to the excavation of entrance section in relevant engineering.

开挖后西南公路隧道入口处出现次生衬砌严重裂缝。隧道入口段具有层状岩体的地质特征，其构造平面倾斜，地形不对称，埋深浅，围岩软。本文旨在探讨入口段衬砌的开裂机理，并提出相应的加固措施，以防止结构破坏。进行现场调查以证明隧道衬砌的开裂特征（过程，分布，宽度和深度）。裂纹主要出现在左足弓和右侧壁的内壁以及右足弓的外壁。对开裂段次生衬砌的变形进行监测和分析，以探讨开裂出现和临时支护安装后的变形特性。然后，建立基于实际地形的三维有限差分数值模型，以分析入口段的空间力学特性。利用包含四个围岩区域的变形分析模型，分析了倾斜弱结构面非对称荷载隧道的开裂机理。最后，提出了地面加固措施和反向荷载控制层状岩体和隧道结构的变形。研究隧道的开裂情况对相关工程入口段的开挖具有重要意义。